WO2015151907A1 - 成形性と焼付け塗装硬化性とに優れたアルミニウム合金板 - Google Patents
成形性と焼付け塗装硬化性とに優れたアルミニウム合金板 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/02—Alloys based on aluminium with silicon as the next major constituent
- C22C21/04—Modified aluminium-silicon alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/02—Alloys based on aluminium with silicon as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
- C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
- C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C2202/00—Physical properties
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
- C22F1/05—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions
Definitions
- the present invention relates to an Al—Mg—Si aluminum alloy sheet.
- the aluminum alloy sheet referred to in the present invention is a rolled sheet such as a hot-rolled sheet or a cold-rolled sheet, and after being subjected to tempering such as a solution treatment and a quenching process, press forming or baking This refers to an aluminum alloy plate that has not been paint hardened.
- aluminum is also referred to as aluminum or Al.
- outer panels such as hoods, fenders, doors, roofs, trunk lids, etc. are also used as thin and high-strength aluminum alloy plates, such as Al-Mg-Si AA to
- JIS 6000 series aluminum hereinafter also simply referred to as 6000 series
- This 6000 series aluminum alloy plate contains Si and Mg as essential components.
- the excess Si type 6000 series aluminum alloy has a composition in which these Si / Mg is 1 or more in mass ratio, and has excellent age hardening ability. Have. For this reason, at the time of press molding or bending to the outer panel of an automobile, formability is ensured by reducing the strength.
- the outer panel of an automobile is manufactured by combining an aluminum alloy plate with a forming process such as an extension forming in a press forming or a bending forming.
- a forming process such as an extension forming in a press forming or a bending forming.
- a large outer panel such as a hood or a door is formed into a molded product shape as an outer panel by press molding such as overhanging, and then an inner panel is formed by processing a hem heel such as a flat hem on the outer peripheral edge of the outer panel.
- a hem heel such as a flat hem on the outer peripheral edge of the outer panel.
- the 6000 series aluminum alloy has the advantage of having excellent BH properties, but has aging property at room temperature, and is age-hardened by holding at room temperature after solution hardening treatment, thereby increasing the strength.
- the moldability, especially the bending workability was reduced.
- a 6000 series aluminum alloy plate is used for an automotive panel application, after being solution-quenched by an aluminum manufacturer (after manufacture), it is left at room temperature for about one month before being molded into a panel by the automobile manufacturer. (Left at room temperature) During this time, it is considerably age hardened (room temperature aging).
- Patent Documents 1 to 3 an attempt to directly measure and control a cluster (aggregate of atoms) affecting BH properties and room temperature aging of a 6000 series aluminum alloy plate has been proposed (Patent Documents 1 to 3).
- clusters (aggregates of atoms) that affect BH properties and room temperature aging are observed by directly analyzing the structure of a plate as it is with a transmission electron microscope of 1 million times.
- the average number density of clusters having a circle equivalent diameter in the range of 1 to 5 nm is defined within a certain range, and is excellent in BH property and suppressed room temperature aging.
- Patent Documents 2 and 3 instead of directly observing clusters (aggregates of atoms) as in Patent Document 1, ionization (electric field) is once performed under a high electric field by a three-dimensional atom probe field ion microscope.
- a set of atoms defined in the atomic structure of the plate reconstructed by analysis is defined from the positional information of the atoms of the evaporated plate. More specifically, it includes at least 10 Mg atoms and / or Si atoms in total, and even if any of the Mg atoms or Si atoms contained therein is used as a reference, it is adjacent to the reference atom.
- An aggregate of atoms that satisfies the condition that the mutual distance to any one of the other matching atoms is 0.75 nm or less is controlled. That is, it defines the average number density, size distribution, or ratio of the aggregate of atoms that satisfies this condition.
- Patent Document 4 proposes a method of combining room temperature aging suppression and BH properties by adding an appropriate amount of Sn and applying preliminary aging after solution treatment.
- Patent Document 5 proposes a method for improving formability, BH property, and corrosion resistance by adding Sn and Cu for improving formability.
- Japanese Unexamined Patent Publication No. 2009-242904 Japanese Unexamined Patent Publication No. 2012-193399 Japanese Unexamined Patent Publication No. 2013-60627 Japanese Unexamined Patent Publication No. 09-249950 Japanese Unexamined Patent Publication No. 10-226894
- one of the factors that make it difficult to apply a high-strength aluminum alloy sheet to such an outer panel is the problem of the shape unique to the outer panel.
- On the outer panel there are partial recesses (projections and embossed parts) with a predetermined depth, such as handle seats, lamp seats, and license plates (license plate) seats, etc. Provided.
- the problem of such surface distortion is not only the problem of the above-mentioned recess (overhanging portion), but also the shape of the door outer panel, the vertical wall of the front fender, the wind corner of the rear fender, the trunk lid and the hood outer.
- This is a problem common to automobile panels, such as the disappearance part of the character line and the base part of the rear fender pillar, which have a part of the concave part (overhanging part) that causes surface distortion.
- the 0.2% proof stress of the plate during press molding should be lowered to less than 110 MPa. Is desired.
- the 0.2% yield strength after baking coating hardening (hereinafter also referred to as after bake hard and BH) is 200 MPa or more, and the 0.2% yield strength increase by baking coating hardening. It becomes difficult to make the amount 100 MPa or more. In the conventional organization control by DSC, it is difficult to solve the problem.
- the first embodiment of the present invention was made to solve the above-described conventional problems, and the 0.2% proof stress at the time of molding an automobile panel was lowered to 110 MPa or less, and the 0.1% after BH was reduced.
- An object of the present invention is to provide an aluminum alloy plate (hereinafter also referred to as a first object) having both formability and bake-coating curability capable of having a 2% proof stress of 200 MPa or more.
- the 0.2% proof stress of the plate during press molding (room temperature aging after manufacture) is lowered to 110 MPa or less.
- the yield ratio which is the ratio of the tensile strength to the yield strength (0.2% proof stress / tensile strength).
- bake hard BH
- the 0.2% yield strength after baking coating hardening treatment (hereinafter also referred to as bake hard, BH) is 190 MPa or more, and the 0.2% yield strength by baking coating hardening. It is difficult to increase the amount to 100 MPa or more.
- the second embodiment of the present invention has been made in order to solve the above-described conventional problems.
- the 0.2% yield strength at the time of automobile panel molding is lowered to 110 MPa or less, and the yield ratio is 0.50. It is possible to increase the 0.2% proof stress after BH to 190 MPa or more, and to achieve both high BH property and low yield ratio. It is an object to provide an aluminum alloy plate (hereinafter also referred to as a second object).
- the gist of the aluminum alloy plate excellent in formability and bake-coating curability according to the first embodiment of the present invention is expressed by mass%, and Mg: 0.2-2
- the endothermic peak corresponding to the dissolution of the Mg—Si cluster has an endothermic peak height in the temperature range of 150 to 230 ° C.
- the peak height of the exothermic peak in the temperature range of 240 to 255 ° C. is 20 ⁇ W / mg or more.
- test equipment DSC220G manufactured by Seiko Instruments
- standard material aluminum
- sample container aluminum
- temperature rising condition 15 ° C./min
- atmosphere argon (50 ml / Min)
- sample weight each performed under the same conditions of 24.5 to 26.5 mg
- the obtained differential thermal analysis profile ( ⁇ W) was divided by the sample weight and normalized ( ⁇ W / mg).
- the region where the profile of differential thermal analysis becomes horizontal is set as a reference level of 0, and the exothermic peak height from this reference level is measured.
- the gist of the aluminum alloy plate excellent in formability and bake coating curability according to the second embodiment of the present invention is mass%, and Mg: 0.3
- the solid solution amount of Mg + Si in the solution separated by the residue extraction method using hot phenol is 1.0% by mass or more and 2.0% by mass or less,
- it contains a total of 10 or more of either Mg atoms or Si atoms, or any of Mg atoms or Si atoms contained in them.
- the range the average volume fraction occupied by the volume V Al ( ⁇ Vi / V Al) ⁇ 100 is 0.3 to 1.5% the aluminum alloy plate was measured by the three-dimensional atom probe field ion microscope Rutotomoni, Of the total volume ⁇ Vi of the atomic aggregate, the average volume fraction ( ⁇ Vi 1.5 or higher ) occupied by the total volume ⁇ Vi 1.5 or higher of the total volume V 1.5 or higher of the atomic aggregate having a Guinier radius r G of 1.5 nm or higher. / ⁇ Vi) ⁇ 100 is 20 to 70%, I will do it.
- Sn captures (captures and traps) atomic vacancies at room temperature in the structure of an Al—Mg—Si-based aluminum alloy plate, so that Mg or Suppresses the diffusion of Si, suppresses the increase in strength at room temperature, and press formability such as hem workability, drawing and overhanging when forming plates into panels (hereinafter referred to as hem (Also called processability).
- hem Also called processability
- Sn can be said to be a side effect of Sn addition.
- the significance of the addition itself may be lost.
- the manufacturing conditions such as preliminary aging treatment (reheating treatment) after the solution hardening treatment are devised, and Sn is added.
- preliminary aging treatment reheating treatment
- Sn is added.
- the reduction of the Mg—Si clusters contributing to the strength and the amount of precipitates deposited after the bake coating hardening treatment were prevented.
- the DSC Differential difference of this plate is used as a measure of the structure to increase or secure the amount of precipitates deposited after baking coating hardening treatment. It was also found that a scanning thermal analysis curve) can be applied. That is, in this embodiment, the DSC regulates an endothermic peak corresponding to dissolution of a relatively small Mg—Si cluster that does not contribute to strength, while generating a relatively large Mg—Si cluster that contributes to strength. Increase the corresponding exothermic peak. As a result, the Mg—Si clusters that do not contribute to the strength are suppressed, and the Mg—Si clusters that contribute to the strength are increased to obtain a desired BH property.
- the 0.2% yield strength at the time of automobile panel molding is lowered to 110 MPa or less, and the 0.2% yield strength after BH is set to 200 MPa or more. It is possible to provide an aluminum alloy plate having both formability and baking coating curability.
- this press formability is also referred to as hem workability.
- the objective is to lower the 0.2% yield strength of the plate at the time of forming to 110 MPa or less and to lower the yield ratio to less than 0.50.
- the solid solution amount of Mg and Si is controlled together with the alloy composition such as Mg and Si. Further, Sn is added to enhance the BH property while ensuring the moldability. As will be described later, Sn is important to achieve both high BH properties and low yield ratio by lowering the volume fraction of atomic aggregates that hinder lower yield ratio even if the solid solution amount of Mg + Si is increased. There is a great effect.
- three-dimensional control is performed in addition to such means so that the yield ratio at the time of forming the plate can be surely lowered to less than 0.50.
- the size distribution of a collection of atoms as measured by an atom probe field ion microscope.
- the aggregate of atoms measured by the three-dimensional atom probe field ion microscope referred to in the present embodiment is a known aggregate of atoms including the measurement methods described in Patent Documents 2 and 3,
- the size and existence form in the structure of the plate is not an atomic assembly (cluster) directly observed in the state of the structure of the plate as it is with a high-magnification TEM.
- the time of flight of the atoms of the plate once ionized (field evaporation) under a high electric field by a three-dimensional atom probe field ion microscope as in Patent Documents 2 and 3, as described later in detail.
- the atomic aggregate is defined as satisfying a certain condition defined in claim 1 (considered as an atomic aggregate).
- the size distribution of the atomic aggregate measured by a three-dimensional atom probe field ion microscope includes the Mg atom or the Si atom,
- the ratio of the aggregate of atoms satisfying the condition that the mutual distance is 0.75 nm or less is restricted to a certain range as the volume fraction.
- the proportion of relatively large aggregates of atoms having the Guinier radius r G of 1.5 nm or more is increased in a certain range as a volume fraction. To do.
- the 0.2% yield strength at the time of automobile panel molding is lowered to 110 MPa or less, and the yield ratio is lowered to less than 0.50, and after BH It is possible to provide an aluminum alloy plate having both formability and bake hardenability that can make the 0.2% yield strength of 190 MPa or more.
- FIG. 1 is an explanatory diagram showing DSCs of examples in the example according to the first embodiment.
- the chemical component composition of the Al—Mg—Si (hereinafter also referred to as 6000) aluminum alloy plate of the present embodiment will be described below.
- the 6000 series aluminum alloy plate targeted by this embodiment is required to have excellent properties such as formability, BH properties, strength, weldability, corrosion resistance, etc. as a plate for an outer plate of an automobile described above. These requirements are also satisfied from the viewpoint of composition.
- Sn is added to suppress the room temperature aging of the manufactured plate, and the 0.2% proof stress at the time of forming the panel is lowered to 110 MPa or less. In particular, it improves the formability of automobile panels and the like where surface distortion becomes a problem.
- the 0.2% proof stress after baking coating is hardened to 200 MPa or more from the viewpoint of composition.
- the composition of the aluminum alloy plate of the present embodiment is, by mass, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0%, Sn: 0 0.005 to 0.3% is included, and the balance is made of Al and inevitable impurities.
- % display of content of each element means the mass% altogether.
- the percentage (mass%) based on mass is the same as the percentage (wt%) based on weight.
- the content of each chemical component may be expressed as “X% or less (excluding 0%)” as “over 0% and X% or less”.
- other elements other than Mg, Si, and Sn are impurities or elements that may be included, and the content level (allowable amount) at each element level in accordance with AA or JIS standards.
- the following elements are allowed to be contained in the range below the upper limit amount in accordance with AA or JIS standard specified below.
- the aluminum alloy plate further comprises Fe: 1.0% or less (excluding 0%), Mn: 1.0% or less (excluding 0%), Cr: 0 .3% or less (excluding 0%), Zr: 0.3% or less (excluding 0%), V: 0.3% or less (excluding 0%), Ti: 0.1% or less (excluding 0%), Cu: 1.0% or less (excluding 0%), Ag: 0.2% or less (excluding 0%), and Zn: 1.0% or less (however, not including 0%), one or more selected from the group consisting of 0% or less may be further included within this range in addition to the basic composition described above.
- the Cu content is preferably 0.7% or less, more preferably 0.3% or less.
- Mn, Fe, Cr, Zr, and V are contained in a large amount, a relatively coarse compound is likely to be generated, and the hem workability (hem bendability) that is a problem in the present embodiment is likely to be deteriorated. Therefore, the Mn content is preferably 0.6% or less, more preferably 0.3% or less, and the Cr, Zr, V content is preferably 0.2% or less, more preferably 0.1% or less. And each.
- Si 0.3 to 2.0% Si, together with Mg, forms aging precipitates that contribute to strength improvement during artificial aging treatment such as paint baking treatment, and exhibits age-hardening ability to obtain the strength (proof strength) required for automobile panels Is an essential element. If the amount of Si added is too small, the amount of precipitation after artificial aging is too small, and the amount of increase in strength during baking is too low. On the other hand, if the Si content is too large, coarse crystallized substances are formed with impurities such as Fe, and formability such as bending workability is remarkably lowered.
- the Si content is in the range of 0.3 to 2.0%.
- the excess Si type is generally referred to as Si / Mg being 1.0 or more in mass ratio. Furthermore, it is preferable to have a 6000 series aluminum alloy composition containing Si in excess relative to Mg.
- Mg 0.2-2.0% Mg is also an important element for cluster formation defined in this embodiment together with Si, and at the time of artificial aging treatment such as paint baking treatment, it forms an aging precipitate that contributes to strength improvement together with Si, and has age hardening ability. It is an indispensable element for exerting the necessary proof strength as a panel. If the Mg content is too small, the amount of precipitation after artificial aging will be too small, and the strength after baking will be too low. On the other hand, if the Mg content is excessively large, coarse crystallized substances are formed with impurities such as Fe, and the formability such as bending workability is remarkably lowered.
- the Mg content is in the range of 0.2 to 2.0%.
- Sn 0.005 to 0.3% Sn captures (captures and traps) atomic vacancies at room temperature, thereby suppressing diffusion of Mg and Si at room temperature, suppressing an increase in strength at room temperature. This has the effect of improving workability, press formability such as drawing and overhanging (hereinafter, this press formability is also referred to as hem workability). And since the vacancies captured during the artificial aging treatment such as the paint baking treatment of the panel are released, the diffusion of Mg and Si can be promoted and the BH property can be increased. If the Sn content is less than 0.005%, the holes cannot be sufficiently trapped and the effect cannot be exhibited.
- the preferable lower limit of Sn content is 0.01%.
- the upper limit with preferable Sn content is 0.2%, Furthermore, 0.1%, More preferably, it is 0.06%.
- the amount of precipitates deposited after baking coating hardening treatment is set in the present embodiment.
- the endothermic peak and the exothermic peak in a specific temperature range which are particularly related to the strength before baking coating and the strength increase during baking coating, are controlled.
- the DSC of this plate is used before baking coating so that the Mg—Si clusters contributing to the strength are not reduced and the amount of precipitates deposited after baking coating hardening is not insufficient. Controls endothermic and exothermic peaks in specific temperature ranges that are particularly relevant for strength and strength increase during baking.
- the DSC regulates an endothermic peak corresponding to the dissolution of a relatively small Mg—Si cluster that does not contribute to the strength, while the relatively large Mg—Si cluster that contributes to the strength.
- the exothermic peak corresponding to the formation of is increased.
- the Mg—Si clusters that do not contribute to the strength are suppressed, and the Mg—Si clusters that contribute to the strength are increased to obtain a desired BH property.
- the differential scanning calorimetry curve refers to the thermal change in the melting process of the aluminum alloy sheet after the tempering treatment from the solid phase obtained by measuring by differential thermal analysis under the conditions described later. It is a heating curve.
- test equipment DSC220G manufactured by Seiko Instruments Inc.
- standard material aluminum
- sample container aluminum
- temperature rising condition 15 ° C./min
- atmosphere After performing under the same conditions of argon (50 ml / min) and sample weight: 24.5 to 26.5 mg, respectively, and normalizing the obtained differential thermal analysis profile ( ⁇ W) by dividing by the sample weight ( ⁇ W / mg)
- the region where the profile of the differential thermal analysis becomes horizontal is set as a reference level of 0, and the exothermic peak height from this reference level is measured.
- the number (number density) of Mg—Si clusters which are recognized as Mg—Si clusters that do not contribute to the strength and are relatively small in size and easily dissolved in the temperature rising process of DSC, is suppressed.
- BH when the number of Mg-Si clusters that are easily dissolved in the DSC temperature rising process increases, conversely, it is recognized that it contributes to the strength.
- the number (number density) of Mg—Si clusters that are difficult to decrease decreases even after artificial age hardening, and the strength after BH does not increase. Specifically, although it depends on the BH condition, a post-BH strength (0.2% proof stress) of 200 MPa or more cannot be obtained with a 0.2% proof stress increase of 100 MPa or more.
- the peak height of the endothermic peak A in the temperature range of 150 to 230 ° C. is assumed as an endothermic peak that does not contribute to the strength and corresponds to the dissolution of the Mg—Si cluster that is easily dissolved in the DSC temperature rising process.
- the peak height of the endothermic peak in the temperature range of 150 to 230 ° C. is 8 ⁇ W / mg, which is an acceptable limit for the adverse effect on the strength of the relatively small size Mg—Si cluster that does not contribute to the strength. Number density is shown.
- This embodiment does not include the case where there is no Mg—Si cluster having a relatively small size that does not contribute to the strength (when the number density is 0) because of the limitation of the production of the plate. Yes. Therefore, the definition that the endothermic peak A has a peak height of 8 ⁇ W / mg or less includes the case of 0 ⁇ W / mg in which there is no Mg—Si cluster having a relatively small size that does not contribute to such strength.
- the BH property is improved by generating a large number of Mg—Si clusters that contribute to strength, are relatively large in size, and are difficult to dissolve in the DSC temperature rising process.
- the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. corresponding to the generation of Mg—Si clusters contributing to the strength is increased (increased) to 20 ⁇ W / mg or more. Therefore, the peak height of the exothermic peak in the temperature range of 240 to 255 ° C. is 20 ⁇ W / mg, although it depends on the BH condition, the target improvement in BH property (0.2% proof stress of 100 MPa or more).
- the minimum number density of Mg—Si clusters having a relatively large size contributing to strength is shown. Therefore, the higher the number density, the better, and the higher (higher) the peak height of the exothermic peak in the temperature range of 240 to 255 ° C. is better, but the upper limit is about 80 ⁇ W / mg from the limit of the production of the plate. .
- Invention Example 8 is a thick solid line and Comparative Example 9 is a dotted line as DSCs of three types of aluminum alloy plates of Invention Example 8 in Table 2, Comparative Example 9 and Comparative Example 25 in Table 3 in Examples described later. Comparative Example 25 is indicated by a dashed line.
- the DSC of Comparative Example 9 has a high (large) peak height of the endothermic peak A in the temperature range of 150 to 230 ° C. exceeding 8 ⁇ W / mg as shown in Table 2 described later, and does not contribute to the strength.
- the number density of Mg-Si clusters having a relatively small size is too large.
- the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. is as high as 20 ⁇ W / mg or more (large), and the number density of Mg—Si clusters having a relatively large size contributing to strength is also large.
- the DSC of Comparative Example 25 in FIG. 1 has a peak height of endothermic peak A in the temperature range of 150 to 230 ° C. as low (small) as 8 ⁇ W / mg or less as shown in Table 2 described later, and does not contribute to strength.
- the number density of relatively small Mg—Si clusters is low.
- the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. is also low (small) less than 20 ⁇ W / mg, and the number density of the relatively large size Mg—Si clusters contributing to the strength is too small. .
- the target BH property (0.2% yield strength after BH of 200 MPa or more with an increase of 0.2% yield strength of 100 MPa or more) is not obtained.
- the DSC of Invention Example 8 in FIG. 1 shows that the peak height of the endothermic peak A in the temperature range of 150 to 230 ° C. is as low as 8 ⁇ W / mg or less (small) as shown in Table 2 described later. The number density of relatively small Mg—Si clusters that do not contribute is low.
- the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. is as high (large) as 20 ⁇ W / mg or more, and the number density of Mg—Si clusters having a relatively large size contributing to the strength is large. For this reason, the target BH property (0.2% yield strength after 100 MPa and 0.2% yield strength after 200 MPa or more) is obtained.
- the aluminum alloy sheet of the present embodiment is a conventional process or a known process, and the aluminum alloy ingot having the above-described 6000 series component composition is subjected to homogenization heat treatment after casting and subjected to hot rolling and cold rolling. Thus, it is manufactured to a predetermined plate thickness and further subjected to a tempering treatment such as solution hardening.
- an ordinary molten casting method such as a continuous casting method and a semi-continuous casting method (DC casting method) is appropriately selected for the molten aluminum alloy adjusted to be dissolved within the above-mentioned 6000 series component composition range.
- DC casting method semi-continuous casting method
- the average cooling rate during casting is as large (fast) as possible from the liquidus temperature to the solidus temperature of 30 ° C./min.
- homogenization heat treatment Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment prior to hot rolling.
- the purpose of this homogenization heat treatment (soaking) is to homogenize the structure, that is, eliminate segregation in crystal grains in the ingot structure.
- the conditions are not particularly limited as long as the object is achieved, and normal one-stage or one-stage processing may be performed.
- the homogenization heat treatment temperature is appropriately selected from the range of 500 ° C. or more and less than the melting point, and the homogenization time is 4 hours or more.
- this homogenization temperature is low, segregation within the crystal grains cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that stretch flangeability and bending workability are deteriorated.
- the hot rolling may be started immediately, or the hot rolling may be started after cooling to an appropriate temperature.
- Hot rolling is composed of an ingot (slab) rough rolling process and a finish rolling process according to the thickness of the rolled sheet.
- a reverse or tandem rolling mill is appropriately used.
- the hot rolling start temperature is preferably 350 ° C. to the solidus temperature, more preferably 400 ° C. to the solidus temperature.
- Hot rolled sheet annealing (Hot rolled sheet annealing) Annealing (roughening) of the hot-rolled sheet before cold rolling is not always necessary, but it can be performed to further improve properties such as formability by refining crystal grains and optimizing the texture. good.
- Cold rolling In cold rolling, the hot-rolled sheet is rolled to produce a cold-rolled sheet (including a coil) having a desired final thickness. However, in order to further refine the crystal grains, the total cold rolling rate is desirably 60% or more regardless of the number of passes.
- the solution hardening treatment may be performed by heating and cooling using a normal continuous heat treatment line, and is not particularly limited. However, since it is desirable to obtain a sufficient solid solution amount of each element and, as described above, it is desirable that the crystal grains are finer, a heating rate of 5 ° C. is applied to a solution treatment temperature of 520 ° C. or higher and a melting temperature or lower. It is desirable that the heating be performed at a rate of 0.1 second / second or more and maintained for 0.1 to 10 seconds.
- the average cooling rate from the solution treatment temperature to the quenching stop temperature at room temperature is preferably 3 ° C./s or more. . If the cooling rate of the quenching treatment to room temperature after the solution treatment is low, coarse Mg—Si and simple substance Si are generated during cooling, and the formability deteriorates. Moreover, the amount of solid solution after solution forming falls, and BH property will fall. In order to ensure this cooling rate, the quenching treatment to room temperature is performed by selecting water cooling means and conditions such as air cooling such as a fan, mist, spray, and immersion.
- Preliminary aging treatment reheating treatment
- the steel sheet is quenched and cooled to room temperature, and then the cold-rolled sheet is subjected to preliminary aging treatment (reheating treatment) within one hour.
- preliminary aging treatment reheating treatment
- the room temperature holding time from the completion of the quenching treatment to room temperature until the start of the pre-aging treatment (heating start) is too long, many small Mg-Si clusters that do not contribute to the above strength are generated as clusters that are easily dissolved by room temperature aging. Therefore, it becomes difficult to suppress the peak height of the endothermic peak in the temperature range of 150 to 230 ° C. to 8 ⁇ W / mg or less. Accordingly, the shorter the room temperature holding time is better, the solution treatment and quenching treatment and the reheating treatment may be continued so that there is almost no time difference, and the lower limit time is not particularly set.
- the temperature rising rate up to the preliminary aging temperature and the holding time in the preliminary aging temperature range are controlled.
- the heating rate is as high as possible (fast) heating rate of 1 ° C./s or more, preferably 5 ° C./s or more, in order to suppress the formation of small Mg—Si clusters that do not contribute to the strength. It is preferable to do.
- the rate of temperature increase is less than 1 ° C / s, many Mg-Si clusters that do not contribute to strength and easily dissolve during DSC temperature increase process are generated, and the endothermic peak in the temperature range of 150 to 230 ° C It becomes difficult to suppress the height to 8 ⁇ W / mg or less.
- the temperature and holding time of the preliminary aging treatment shall be held for 10 hours or more and 40 hours or less in the temperature range of 60 to 120 ° C.
- the temperature holding at 60 to 120 ° C. may be a heat treatment in which the temperature is sequentially changed within this temperature range by a constant temperature or by raising and lowering the temperature. In short, even if the temperature continuously changes due to slow cooling, temperature rise or the like, it may be held in the temperature range of 60 to 120 ° C. for 10 hours or more and 40 hours or less.
- the BH property decreases.
- the amount of precipitation nuclei generated in the preliminary aging treatment is excessively increased.
- relatively large Mg—Si clusters contributing to the strength are reduced, and the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. in DSC is as high as 20 ⁇ W / mg or more ( BH properties are also reduced.
- molding also becomes high too much.
- the 0.2% yield strength at the time of molding an automobile panel is lowered to 110 MPa or less, and the 0.2% yield strength after BH is set to 200 MPa or more. Becomes difficult.
- the chemical component composition of the Al—Mg—Si (hereinafter also referred to as 6000) aluminum alloy plate of the present embodiment will be described below.
- the 6000 series aluminum alloy plate targeted by this embodiment is required to have excellent properties such as formability, BH properties, strength, weldability, corrosion resistance, etc. as a plate for an outer plate of an automobile described above. These requirements are also satisfied from the viewpoint of composition.
- Sn is contained to suppress room temperature aging of the manufactured plate, lower the 0.2% proof stress during panel forming to 110 MPa or less, and the yield ratio to 0.50. By lowering to less than the range, the formability of the automobile panel structure, such as an automobile panel in which surface distortion becomes a problem, is improved.
- the 0.2% proof stress after baking finish is set to 190 MPa or more from the viewpoint of composition.
- the composition of the aluminum alloy plate of the present embodiment is, by mass, Mg: 0.3 to 1.0%, Si: 0.5 to 1.5%, Sn: 0 0.005 to 0.3% is included, and the balance is made of Al and inevitable impurities.
- % display of content of each element means the mass% altogether.
- the percentage (mass%) based on mass is the same as the percentage (wt%) based on weight.
- the content of each chemical component may be expressed as “X% or less (excluding 0%)” as “over 0% and X% or less”.
- other elements other than Mg, Si, and Sn are impurities or elements that may be included, and the content level (allowable amount) at each element level in accordance with AA or JIS standards.
- the following other elements are allowed to be contained in the range of the upper limit amount or less in accordance with the AA to JIS ⁇ standards defined below. To do.
- the aluminum alloy plate further comprises Fe: 1.0% or less (excluding 0%), Mn: 0.4% or less (excluding 0%), Cr: 0 .3% or less (excluding 0%), Zr: 0.3% or less (excluding 0%), V: 0.3% or less (excluding 0%), Ti: 0.1% or less (excluding 0%), Cu: 0.4% or less (excluding 0%), Ag: 0.2% or less (excluding 0%), and Zn: 1.0% or less (however, not including 0%), one or more selected from the group consisting of 0% or less may be further included within this range in addition to the basic composition described above.
- the Cu content tends to deteriorate the corrosion resistance, so the Cu content is preferably 0.3% or less.
- the Mn content is preferably 0.35% or less, and the Cr, Zr, V content is preferably 0.2% or less, more preferably 0.1% or less.
- Si 0.5 to 1.5% Si, together with Mg, forms aging precipitates that contribute to strength improvement during artificial aging treatment such as paint baking treatment, and exhibits age-hardening ability to obtain the strength (proof strength) required for automobile panels Is an essential element.
- Solid solution Si is an element that improves work hardening ability, and when dissolved, the yield ratio, which is the ratio of tensile strength to yield strength (0.2% proof stress / tensile strength), is reduced to less than 0.50. effective.
- the Si content is too small, the amount of precipitates after the artificial age hardening treatment will be too small, the amount of increase in strength during baking coating will be low, and the amount of dissolved Si will also be small, resulting in a yield ratio exceeding 0.50. It becomes too big.
- the Si content is too large, coarse crystallized substances are formed with impurities such as Fe, and formability such as bending workability is remarkably lowered.
- the Si content is too high, not only the strength immediately after the production of the plate, but also the room temperature aging amount after the production becomes high, the strength before molding becomes too high, and particularly the surface distortion of the panel structure of an automobile. However, the moldability of automobile panels and the like that would cause a problem is reduced. Therefore, the Si content is in the range of 0.5 to 1.5%.
- Si / Mg is set to 1.0 or more in mass ratio, and generally called excess Si type Furthermore, it is preferable to have a 6000 series aluminum alloy composition containing Si in excess relative to Mg.
- Mg 0.3 to 1.0% Mg, together with Si, is an important element for forming an aggregate of atoms as defined in the present embodiment.
- aging precipitates that contribute to strength improvement are formed together with Si. It is an indispensable element for exhibiting the curing ability and obtaining the necessary proof strength as a panel.
- solid solution Mg is an element that improves work hardening ability, and when dissolved, the yield ratio, which is the ratio of tensile strength to yield strength (0.2% proof stress / tensile strength), is 0.50. There is an effect of lowering below.
- the Mg content is in the range of 0.3 to 1.0%.
- the Sn content is less than 0.005%, even if the solid solution amount of Mg + Si described above is increased, the volume fraction of the atomic aggregate that inhibits the low yield ratio is lowered, and the high BH property and the low content are reduced. The effect of achieving both yield ratio and the effect of suppressing the above-described room temperature age hardening cannot be exhibited.
- the Sn content is more than 0.3%, Sn is segregated at the grain boundaries and easily causes grain boundary cracking.
- the preferable lower limit of Sn content is 0.01%.
- the upper limit with preferable Sn content is 0.2%, Furthermore, 0.1%, More preferably, it is 0.06%.
- the total solid solution amount of Mg and Si contained in the plate (Mg + Si solid solution amount) is increased in the present embodiment. It is secured within a certain range of 0.0 mass% or more and 2.0 mass% or less. If the solid solution amount of Mg + Si is less than 1.0% by mass, the BH property cannot be secured even with the above composition. The higher the solid solution amount of Mg + Si, the better the BH property. However, the Mg and Si content and the solid solution amount have the above-described composition and manufacturing restrictions. There is also a problem that the volume fraction of the atomic aggregate is increased and the yield strength and yield ratio of the panel are increased, and the upper limit is set to 2.0% by mass.
- Measurement of the solid solution amount of Mg + Si on the plate is a solution obtained by dissolving the sample of the plate to be measured by hot phenol residue extraction method, and filtering and separating the solid and liquid using a filter with a mesh of 0.1 ⁇ m.
- the total content of Mg and Si is regarded as the solid solution amount of Mg + Si.
- the residue extraction method using hot phenol is specifically performed as follows. First, after putting phenol into a decomposition flask and heating, each sample plate sample to be measured is transferred to this decomposition flask and thermally decomposed. Next, after adding benzyl alcohol, it is filtered by suction through the filter, the solid-liquid is separated by filtration, and the total content of Mg and Si in the separated solution is quantitatively analyzed. For this quantitative analysis, atomic absorption spectrometry (AAS), inductively coupled plasma emission spectrometry (ICPOES), or the like is appropriately used. As described above, a membrane filter having a mesh (collected particle diameter) of 0.1 ⁇ m and a diameter of 47 mm is used for the suction filtration. This measurement and calculation were performed on three samples taken from a total of three locations, one central portion in the plate width direction of the test plate and two end portions in the plate width direction from this central portion. The solid solution amount (mass%) of Mg + Si is averaged.
- AAS
- the structure of the 6000 series aluminum alloy sheet is further reduced to a yield ratio of less than 0.50 and three-dimensional to guarantee the BH property. Controls the size distribution of the aggregate of atoms of Mg and Si measured by an atom probe field ion microscope. As a result, not only the above-described effect of Sn but also an atomic assembly (cluster) in the structure of the plate is controlled to achieve both a high BH property and a low yield ratio.
- the aggregate of atoms defined in the present embodiment is measured by directly observing the structure of the plate as it is with a high-magnification TEM (Transmission Electron Microscope) as in Patent Document 1. It is not a cluster (cluster) of real atoms in the 6000 series aluminum alloy plate. However, it is deeply correlated with the state of existence of actual atomic aggregates (clusters) in the 6000 series aluminum alloy plate as directly observed by the high magnification TEM. For this reason, even if the measurement of the atomic aggregate in the present embodiment is indirect or simulated, the actual atomic aggregate (cluster) that greatly influences the low yield ratio and the high BH property. ) Is well correlated, and serves as a standard for guaranteeing a low yield ratio and a high BH property from the viewpoint of the structure (atom assembly).
- TEM Transmission Electron Microscope
- the plate to be measured is a 6000 series aluminum alloy plate after tempering such as solution treatment and quenching treatment and before press forming or baking coating hardening treatment, and this plate
- board thickness center parts is measured with a three-dimensional atom probe field ion microscope.
- the conditions to be satisfied as an atomic aggregate in the present embodiment are the same as those in Patent Documents 2 and 3.
- a total of 10 or more of either Mg atoms or Si atoms or both are assumed to be included.
- the upper limit of the number of Mg atoms and Si atoms contained in the aggregate of atoms is not particularly specified, but from the production limit, the upper limit of the number of Mg atoms and Si atoms contained in the aggregate of atoms is approximately 10,000. About one.
- the mutual distance between the reference atom and any of the other atoms adjacent to each other is What is 0.75 nm or less is defined as an aggregate of atoms. This mutual distance of 0.75 nm has not been fully clarified in technical terms, but the distance between atoms of Mg and Si is close to each other, which greatly affects low yield ratio and high BH properties. This is an experimentally determined value for prescribing the aggregate of atoms of a certain size and its volume fraction with good reproducibility.
- the aggregate of atoms defined in the present embodiment most often includes both Mg atoms and Si atoms, but includes Mg atoms but does not include Si atoms, or includes Si atoms but does not include Mg atoms. Including cases. Moreover, it is not necessarily comprised only by Mg atom or Si atom, In addition to these, Al atom is included with very high probability.
- atoms such as Fe, Mn, Cu, Cr, Zr, V, Ti, Zn, or Ag contained as alloy elements or impurities are included in the aggregate of atoms. It inevitably occurs when a number of atoms are counted by 3DAP analysis. However, even if these other atoms (from alloy elements and impurities) are included in the aggregate of atoms, the level is smaller than the total number of Mg atoms and Si atoms. Therefore, even when such other atoms are included in the aggregate of atoms, those satisfying the above definition (conditions) are atoms composed only of Mg atoms and Si atoms as the aggregate of atoms of the present embodiment. Functions in the same way as Therefore, the aggregate of atoms defined in the present embodiment may include any other atom as long as the above-described definition is satisfied.
- the reference is based on any of the Mg atoms and Si atoms contained therein, the mutual distance between the reference atom and any one of the other adjacent atoms is 0. .75 nm or less "means that all Mg atoms and Si atoms present in the aggregate of atoms have at least one Mg atom or Si atom having a distance of 0.75 nm or less around each other. It means that
- the definition of the distance between atoms is based on any one of Mg atoms or Si atoms contained therein, among other atoms adjacent to the reference atom.
- the distances of all the atoms may not all be 0.75 nm or less, and conversely, all may be all 0.75 nm or less.
- other Mg atoms or Si atoms having a distance exceeding 0.75 nm may be adjacent to each other, and the specified distance (interval) is satisfied around a specific (reference) Mg atom or Si atom.
- the number of Mg atoms or Si atoms that satisfy the distance condition is specified (reference) Mg.
- the number of Mg atoms or Si atoms that satisfy the distance condition is specified (reference) Mg.
- the number of Mg atoms or Si atoms to be counted that satisfy the distance condition is a specific (reference) Mg
- the number is 3 including atoms or Si atoms.
- each aggregate of atoms is regarded as a sphere as the total volume of the atomic aggregate that satisfies certain conditions such as the number of Mg atoms and Si atoms and the distance between atoms described above.
- the Guinier radius r G of the total volume ⁇ Vi of the atomic aggregate among the atomic aggregates that satisfy the above condition is used.
- the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) occupying the total volume ⁇ Vi 1.5 or more of the aggregate of atoms having a diameter of 1.5 nm or more is controlled in the range of 20 to 70%.
- the aggregate of the satisfying individual atoms is divided by Guinier radius r G 1.5nm, Guinier radius r G is the sum of the volume Vi 1.5 or more sets of individual atoms is 1.5nm or more
- the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 of the total volume ⁇ Vi 1.5 or more in the total volume V of the atomic assembly is controlled in the range of 20 to 70%.
- the Guinier radius r G is a rotation of an aggregate of atoms when the aggregate of atoms satisfying the above condition is regarded as a sphere.
- the definition of this Guinier radius and the calculation method mentioned later are well-known by the said patent documents 2.
- the 0.2% proof stress during molding of automobile panels of 6000 series aluminum alloy sheets is lowered to 110 MPa or less, and the yield ratio is lowered to less than 0.50.
- the 0.2% yield strength after BH can be 190 MPa or more.
- the average volume fraction ( ⁇ Vi / V Al ) ⁇ 100 of the aggregate of atoms satisfying the above conditions is less than 0.3%, it is effective for high BH property and low yield ratio, and the Guinier radius r G is 1.5 nm. The absolute number of these relatively large aggregates of atoms is insufficient. For this reason, even if the composition is satisfied, the high BH property and the low yield ratio cannot be achieved. On the other hand, even if the average volume fraction ( ⁇ Vi / V Al ) ⁇ 100 exceeds 1.5%, the number of atomic aggregates that satisfy the condition that the distance from each other is 0.75 nm or less Therefore, it is impossible to reduce the 0.2% yield strength and lower the yield ratio when forming the panel.
- the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 of an aggregate of relatively large atoms having a Guinier radius r G of 1.5 nm or more is less than 20%.
- the yield ratio can be reduced. Cannot be achieved.
- the yield ratio can be reduced, but the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 , Exceeding 70% is difficult in manufacturing, and the upper limit is made 70% from the manufacturing limit.
- 3DAP three-dimensional atom probe
- FIM field ion microscope
- the local analyzer is capable of observing individual atoms on a metal surface with a field ion microscope and identifying these atoms by time-of-flight mass spectrometry.
- 3DAP is a very effective means for structural analysis of atomic aggregates because it can simultaneously analyze the type and position of atoms emitted from a sample.
- This 3DAP uses an ionization phenomenon of sample atoms under a high electric field called field evaporation.
- field evaporation When a high voltage necessary for the field evaporation of sample atoms is applied to the sample, the atoms are ionized from the sample surface and pass through the probe hole to reach the detector.
- This detector is a position-sensitive detector, and it is detected by measuring the time of flight to the individual ion detector along with mass analysis of individual ions (identification of elements that are atomic species).
- the determined position (atomic structure position) can be determined simultaneously. Therefore, 3DAP has the feature that the atomic structure at the tip of the sample can be reconstructed and observed three-dimensionally because the position and atomic species of the atom at the tip of the sample can be measured simultaneously. Further, since field evaporation occurs sequentially from the tip surface of the sample, the distribution of atoms in the depth direction from the sample tip can be examined with atomic level resolution.
- the sample to be analyzed must be highly conductive, such as metal, and the shape of the sample is generally very fine with a tip diameter of around 100 nm ⁇ or less. Need to be needle-shaped. For this reason, a sample is taken from the central part of the thickness of the aluminum alloy plate to be measured, and this sample is cut and electropolished with a precision cutting device to obtain a sample having an ultra-fine needle tip for analysis. Make it.
- a measuring method for example, using “LEAP3000” manufactured by Imago Scientific Instruments Inc., a high pulse voltage of 1 kV order is applied to an aluminum alloy plate sample whose tip is shaped like a needle, and several millions from the sample tip.
- the analysis of the atomic aggregate is further performed on this three-dimensional atom map using the Maximum-Separation-Method, which is a method for defining the atoms belonging to precipitates and atomic aggregates.
- the number of Mg atoms or Si atoms or both total of 10 or more
- the distance (interval) between adjacent Mg atoms or Si atoms and the specific narrow interval
- the number of Mg atoms or Si atoms having (0.75 nm or less) is given as a parameter.
- Mg atoms and Si atoms in total of 10 or more, even if any atom of Mg atoms or Si atoms contained in these is used as a reference, other atoms adjacent to the reference atom
- a group of atoms having a distance of 0.75 nm or less and satisfying these conditions is defined as a group of atoms of the present embodiment. Then, the dispersion state of the atomic aggregates that meet this definition is evaluated, and the number density of the atomic aggregates is averaged over three or more measurement samples to obtain an average density per 1 m 3 (number / piece m 3 ) Measure and quantify.
- Equation (1 ) lg is a radius of rotation automatically calculated by software unique to the three-dimensional atom probe field ion microscope.
- x, y, and z are invariant x, y, and z axes in the measurement layout of the three-dimensional atom probe field ion microscope.
- x i , y i , and z i are the lengths of the x, y, and z axes, and are the spatial coordinates of the Mg and Si atoms that constitute the aggregate of atoms. “X”, etc.
- n is the number of Mg and Si atoms constituting the aggregate of atoms.
- the volume of the needle-shaped sample evaporated (disappeared by field evaporation) is defined as the volume V Al of the aluminum alloy plate measured by a three-dimensional atom probe field ion microscope, and the total of the aggregate of the atoms occupying this volume
- the volume average volume fraction ( ⁇ Vi / V Al ) ⁇ 100 is determined.
- the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 of the total volume ⁇ Vi 1.5 or more of the aggregate of atoms having a Guinier radius r G of 1.5 nm or more in the total volume V of the aggregate of atoms ⁇ 100 also ask.
- the measurement of the average volume fraction of the aggregate of atoms by these 3DAP is carried out at 10 locations in the central part of the arbitrary thickness of the 6000 series aluminum alloy sheet after the tempering. (Calculated value) is averaged.
- the detection efficiency of these atoms by 3DAP is currently limited to about 50% of the ionized atoms, and the remaining atoms cannot be detected. If the detection efficiency of atoms by this 3DAP changes greatly, such as in the future, the measurement result by 3DAP of the average number density (pieces / ⁇ m 3 ) of the aggregate of atoms of each size specified by this embodiment will change. There is a possibility of coming. Therefore, in order to have reproducibility in this measurement, it is preferable that the detection efficiency of atoms by 3DAP is substantially constant at about 50%.
- the aluminum alloy sheet of the present embodiment is a conventional process or a known process, and the aluminum alloy ingot having the above-described 6000 series component composition is subjected to homogenization heat treatment after casting and subjected to hot rolling and cold rolling. Thus, it is manufactured to a predetermined plate thickness and further subjected to a tempering treatment such as solution hardening.
- the preliminary aging treatment conditions after the quenching treatment are set in a preferable range.
- an ordinary molten casting method such as a continuous casting method and a semi-continuous casting method (DC casting method) is appropriately selected for the molten aluminum alloy adjusted to be dissolved within the above-mentioned 6000 series component composition range.
- DC casting method semi-continuous casting method
- the average cooling rate during casting is as large (fast) as possible from the liquidus temperature to the solidus temperature of 30 ° C./min.
- Preliminary aging treatment reheating treatment
- the steel sheet is quenched and cooled to room temperature, and then the cold-rolled sheet is subjected to a pre-aging treatment (reheating treatment) within as short a time as possible within 1 hour (60 minutes).
- a set of atoms that satisfy the conditions of the number of Mg atoms and the number of Si atoms and the interatomic distance if the room temperature holding time until the start of pre-aging treatment (heating start) exceeds 1 hour after the quenching treatment to room temperature is too long The total volume of the body cannot be restricted to an average volume fraction of 1.5% or less.
- the average volume fraction of the aggregates of atoms having a Guinier radius r G of 1.5 nm or more is set to 20% or more. You can't do much.
- the BH property is lowered and it is difficult to reduce the yield ratio. Accordingly, the shorter the room temperature holding time is better, the solution treatment and quenching treatment and the reheating treatment may be continued so that there is almost no time difference, and the lower limit time is not particularly set.
- the temperature increase rate up to the preliminary aging temperature and the holding time in the preliminary aging temperature range are controlled.
- the heating rate is as high as possible (fast) heating rate of 1 ° C./s or more, preferably 5 ° C./s or more, in order to suppress the formation of small atomic aggregates that do not contribute to the above-described strength. It is preferable to do.
- the rate of temperature increase is less than 1 ° C./s, many small atomic aggregates that do not contribute to the strength are generated, and among the atomic aggregates that satisfy the above conditions, the Guinier radius r G is 1.5 nm or more. It becomes impossible to increase the average volume fraction of the aggregate of atoms as 20% or more. As a result, the BH property decreases, and the low yield ratio becomes difficult.
- the temperature and holding time of the preliminary aging treatment shall be held for 10 hours or more and 40 hours or less in the temperature range of 60 to 120 ° C.
- the temperature holding at 60 to 120 ° C. may be a heat treatment in which the temperature is sequentially changed within this temperature range by a constant temperature or by raising and lowering the temperature. In short, even if the temperature continuously changes due to slow cooling, temperature rise or the like, it may be held in the temperature range of 60 to 120 ° C. for 10 hours or more and 40 hours or less.
- the preliminary aging temperature is less than 60 ° C. or the holding time is less than 10 hr, the formation of precipitation nuclei is insufficient, and among the aggregate of atoms satisfying the above conditions, the Guinier radius r G is 1.5 nm or more. The average volume fraction of an aggregate of atoms cannot be increased to more than 20%. As a result, the BH property decreases.
- the amount of precipitation nuclei generated in the preliminary aging treatment is excessively increased. For this reason, the aggregate of relatively large atoms contributing to the strength is decreased, and the average volume fraction of the aggregate of atoms satisfying the above condition exceeds 1.5% and is increased during molding. The yield ratio of the plate cannot be lowered to less than 0.50.
- the 0.2% proof stress of the plate at the time of molding the automobile panel is lowered to 110 MPa or less, and the yield ratio is also lowered to less than 0.50, It becomes difficult to set the 0.2% yield strength after BH to 190 MPa or more.
- 6000 series aluminum alloy plates having different structures defined by DSC were produced by changing the conditions of the pre-aging treatment after solution treatment and quenching treatment. Then, after maintaining the plate at room temperature for 30 days, BH properties (coating bake hardenability), As yield strength as an index of press formability, and hemmability as bending workability were measured and evaluated.
- the 6000 series aluminum alloy plate having the composition shown in Table 1 is prepared as shown in Tables 2 and 3, and the average cooling rate of the quenching treatment after the solution treatment and the subsequent pre-aging.
- Various conditions such as processing temperature and holding time were changed.
- the display of the content of each element in Table 1 the display in which the numerical value of each element is blank indicates that the content is below the detection limit.
- the specific production conditions for the aluminum alloy plate were as follows.
- Aluminum alloy ingots having respective compositions shown in Table 1 were commonly melted by DC casting.
- the average cooling rate during casting was set to 50 ° C./min from the liquidus temperature to the solidus temperature.
- the ingot was subjected to only one-step soaking at 540 ° C. for 6 hours in common with each example, and then hot rough rolling was started at that temperature.
- it was hot rolled to a thickness of 3.5 mm in the subsequent finish rolling to obtain a hot rolled sheet.
- the aluminum alloy sheet after hot rolling is commonly used in each example, and after subjecting to 500 ° C. ⁇ 1 minute of rough annealing, cold rolling is performed at a processing rate of 70% without intermediate annealing in the middle of the cold rolling pass, A cold-rolled plate having a thickness of 1.0 mm was used.
- each cold-rolled sheet was tempered continuously (T4) while being rewound and wound up in a continuous heat treatment facility in common with each example.
- the solution treatment is performed by setting the average heating rate up to 500 ° C. to 10 ° C./second and holding it for 10 seconds after reaching the target temperature of 560 ° C.
- each average cooling shown in Tables 2 and 3 is performed. It cooled to room temperature by performing water cooling or air cooling so that it might become speed.
- preliminary aging treatment was performed using the atmospheric furnace and oil bath at the rate of temperature rise, ultimate temperature, average cooling rate, and holding time shown in Tables 2 and 3. It was.
- the cooling after the preliminary aging treatment was performed by water cooling or slow cooling (cooling) in order to change the average cooling rate.
- each test plate was blanked from each final product plate after being left at room temperature for 30 days, and the DSC and characteristics of each test plate were measured and evaluated. These results are shown in Table 3.
- DSC Differential scanning calorimetry curve
- test equipment DSC220G manufactured by Seiko Instruments Inc.
- standard material aluminum
- sample container aluminum
- temperature rising condition 15 ° C./min
- atmosphere argon (50 ml / Min)
- sample weight each performed under the same conditions of 24.5 to 26.5 mg
- ⁇ W differential thermal analysis profile
- the region where the differential thermal analysis profile was horizontal was defined as a reference level of 0, and the exothermic peak height from this reference level was measured.
- JISZ2201 No. 5 test pieces 25 mm ⁇ 50 mmGL ⁇ plate thickness
- the tensile direction of the test piece at this time was the direction perpendicular to the rolling direction.
- the tensile speed was 5 mm / min up to 0.2% proof stress and 20 mm / min after proof stress.
- the N number for the measurement of mechanical properties was 5, and each was calculated as an average value.
- the test piece for measuring the yield strength after the BH was subjected to the BH treatment after giving a pre-strain of 2% simulating press forming of the plate to the test piece by the tensile tester.
- Hem workability Hem workability was measured only for each test plate after standing at room temperature for 30 days after the tempering treatment.
- a strip-shaped test piece with a width of 30 mm was used, and after bending 90 ° with an internal bend R of 1.0 mm by a down flange, a 1.0 mm thick inner was sandwiched, and the bent portion was further bent inwardly to about 130 degrees.
- Pre-hem processing was performed, and flat hem processing was performed in which the end was closely attached to the inner by bending 180 degrees.
- the surface state of the flat hem bent portion (edge curved portion) such as rough skin, minute cracks, and large cracks was visually observed and visually evaluated according to the following criteria. Based on the following criteria, 0 to 2 are acceptable lines, and 3 or more are unacceptable. 0: No cracking, rough skin, 1: Mild rough skin, 2: Deep rough skin, 3: Small surface crack, 4;
- Inventive numbers 0 to 1, 8, 13 in Table 2 and 16 to 24 in Table 3 using alloy numbers 0 to 12 in Table 1 are within the component composition range of this embodiment and are in a preferable condition range.
- a tempering process including a solution hardening process and a pre-aging process is also performed under preferable conditions.
- these invention examples satisfy the DSC conditions defined in the present embodiment. That is, in the DSC of this plate, as the endothermic peak corresponding to the dissolution of Mg—Si clusters not contributing to the strength, the peak height of the endothermic peak in the temperature range of 150 to 230 ° C. is 8 ⁇ W / mg or less. As the exothermic peak corresponding to the formation of Mg—Si clusters contributing to the peak temperature, the exothermic peak in the temperature range of 240 to 255 ° C. has a peak height of 20 ⁇ W / mg or more.
- each invention example is excellent in BH property even after the tempering treatment at room temperature after aging and at the low temperature and short time.
- Table 3 even after room temperature aging after the tempering treatment, the As yield strength is relatively low, so that it is excellent in press formability to an automobile panel and the like, and is excellent in hem workability. That is, according to the example of the present invention, even when the body paint baking treatment is performed after aging at room temperature, a high BH having a 0.2% proof stress difference of 100 MPa or more and a 0.2% proof stress after BH of 170 MPa or more. And a press formability of 110 MPa or less and an excellent bending workability with an As 0.2% proof stress.
- Comparative Examples 2 to 7, 9 to 13, 14, and 15 in Table 2 use the same alloy examples 1, 2, and 3 as the invention examples in Table 1.
- the pre-aging treatment conditions are not preferable.
- the DSC deviates from the range defined in the present embodiment, and the room temperature aging is larger than that of the invention example having the same alloy composition. It is inferior in press formability and hem workability, and inferior in BH property.
- the average cooling rate in the quenching treatment to room temperature after the solution treatment is too small. Therefore, although the peak height of the endothermic peak A in the temperature range of 150 to 230 ° C. is 8 ⁇ W / mg or less, the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. is as low as less than 20 ⁇ W / mg ( Small), and the number density of Mg—Si clusters having a relatively large size contributing to strength is small. This is because the cooling rate of the quenching treatment to room temperature is small, and coarse Mg 2 Si and simple substance Si are generated during cooling, and the press formability of 110 MPa or less with the target As 0.2% proof stress and Good bending workability is not obtained. Moreover, BH property is also low.
- the retention time in the range of 60 to 120 ° C. in the preliminary aging treatment is too long as 48 hours.
- the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. is as low (small) as less than 20 ⁇ W / mg, and the number density of Mg—Si clusters having a relatively large size contributing to strength is small.
- the target As0.2% yield strength of 110 MPa or less and good bending workability are not obtained.
- BH property is also low.
- the reached temperature in the pre-aging treatment is 130 ° C., which is too high, exceeding the upper limit of 120 ° C.
- the relatively large size Mg—Si clusters that contribute to the strength are reduced, and the peak height of the exothermic peak B in the temperature range of 240 to 255 ° C. is low (small), less than 20 ⁇ W / mg.
- the number density of Mg—Si clusters with relatively large contributing size is small.
- the As 0.2% yield strength is too high exceeding 110 MPa, and neither press formability nor good bending workability is obtained.
- Comparative Examples 25 to 34 in Table 3 are manufactured within a preferable range including the pre-aging treatment conditions, but use Alloy Nos. 13 to 22 in Table 1 and contain Mg and Si as essential elements. Each amount is out of the range of the present embodiment, or the amount of impurity elements is too large. For this reason, as shown in Table 3, these Comparative Examples 24 to 33 have a relatively high As yield strength after holding at room temperature for 30 days, as compared with each invention example. It is inferior in workability or BH property.
- the comparative example 25 is the alloy 13 of Table 1, and there is too little Si.
- the comparative example 26 is the alloy 14 of Table 1, and there is too much Si.
- the comparative example 276 is the alloy 15 of Table 1, and there is too little Sn.
- Comparative example 28 is alloy 16 of Table 1, and there was too much Sn, the crack was produced at the time of hot rolling, and the board was not able to be manufactured.
- the comparative example 29 is the alloy 17 of Table 1, and there is too much Fe.
- the comparative example 30 is the alloy 18 of Table 1, and there is too much Mn.
- the comparative example 31 is the alloy 19 of Table 1, and there are too many Cr and Ti.
- the comparative example 32 is the alloy 20 of Table 1, and there is too much Cu.
- the comparative example 33 is the alloy 21 of Table 1, and there is too much Zn.
- Comparative example 34 is alloy 22 of Table 1 with too much Zr and V.
- 6000 series aluminum alloy plates having different structures defined in the present embodiment were manufactured separately by changing the conditions of the pre-aging treatment after solution treatment and quenching treatment. Then, after maintaining the plate at room temperature for 30 days, BH properties (coating bake hardenability), As yield strength as an index of press formability, and hemmability as bending workability were measured and evaluated.
- the specific production conditions for the aluminum alloy plate were as follows.
- Aluminum alloy ingots having respective compositions shown in Table 4 were commonly melted by DC casting.
- the average cooling rate during casting was set to 50 ° C./min from the liquidus temperature to the solidus temperature.
- the ingot was subjected to only one-step soaking at 540 ° C. for 6 hours in common with each example, and then reheated to 500 ° C. to start hot rough rolling. And in each example, it was hot rolled to a thickness of 3.5 mm in the subsequent finish rolling to obtain a hot rolled sheet.
- the aluminum alloy sheet after hot rolling is commonly used in each example, and after subjecting to 500 ° C. ⁇ 1 minute of rough annealing, cold rolling is performed at a processing rate of 70% without intermediate annealing in the middle of the cold rolling pass, A cold-rolled plate having a thickness of 1.0 mm was used.
- each cold-rolled sheet was tempered continuously (T4) while being rewound and wound up in a continuous heat treatment facility in common with each example.
- the solution treatment is performed by setting the average heating rate up to 500 ° C. to 10 ° C./second and holding it for 10 seconds after reaching the target temperature of 560 ° C.
- each average cooling shown in Tables 5 and 6 is performed. It cooled to room temperature by performing water cooling or air cooling so that it might become speed. After this cooling, after the required time shown in Table 2 at room temperature, using an atmospheric furnace and an oil bath, preliminary aging treatment was performed at the rate of temperature rise, ultimate temperature, average cooling rate, and holding time shown in Tables 5 and 6 It was.
- the cooling after the preliminary aging treatment was performed by water cooling or slow cooling (cooling) in order to change the average cooling rate.
- test plate candy (blank) candy was cut out from each final product plate after being left at room temperature for 30 days, and the structure and properties of each test plate were measured and evaluated. These results are shown in Tables 5 and 6.
- the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 of the total volume ⁇ Vi 1.5 or more of the aggregate of atoms having a Guinier radius r G of 1.5 nm or more in the total volume ⁇ Vi of the atomic assembly (It was described as ⁇ Vi 1.5 or more / ⁇ Vi ⁇ 100 in Tables 5 and 6).
- JISZ2201 No. 5 test pieces 25 mm ⁇ 50 mmGL ⁇ plate thickness
- the tensile direction of the test piece at this time was the direction perpendicular to the rolling direction.
- the tensile speed was 5 mm / min up to 0.2% proof stress and 20 mm / min after proof stress.
- the N number for the measurement of mechanical properties was 5, and each was calculated as an average value.
- the test piece for measuring the yield strength after the BH was subjected to the BH treatment after giving a pre-strain of 2% simulating press forming of the plate to the test piece by the tensile tester.
- Hem workability Hem workability was measured only for each test plate after standing at room temperature for 7 days or 100 days after the tempering treatment.
- a strip-shaped test piece with a width of 30 mm was used, and after bending 90 ° with an internal bend R of 1.0 mm by a down flange, a 1.0 mm thick inner was sandwiched, and the bent portion was further bent inwardly to about 130 degrees.
- Pre-hem processing was performed, and flat hem processing was performed in which the end was closely attached to the inner by bending 180 degrees.
- the surface state of the flat hem bent portion (edge curved portion) such as rough skin, minute cracks, and large cracks was visually observed and visually evaluated according to the following criteria. Based on the following criteria, 0 to 2 are acceptable lines, and 3 or more are unacceptable. 0: No cracking, rough skin, 1: Mild rough skin, 2: Deep rough skin, 3: Small surface crack, 4;
- Inventive examples Nos. 35, 36, 43 and 48 in Table 5, and Nos. 51 to 58 in Table 6 using alloy Nos. 23 to 34 in Table 4 are within the component composition range of the present embodiment and are in a preferable condition range.
- a tempering process including a solution hardening process and a pre-aging process is also performed under preferable conditions.
- each of these inventive examples satisfies the organizational conditions defined in this embodiment. That is, the electric field evaporation of the total volume ⁇ Vi of the aggregate of atoms having a solid solution amount of the Mg + Si of 1.0% by mass or more and 2.0% by mass or less and satisfying the conditions defined in the embodiment.
- the average volume fraction ( ⁇ Vi / V Al ) ⁇ 100 occupying the volume V Al of the needle-shaped sample is in the range of 0.3 to 1.5%, and occupying the total volume ⁇ Vi of the aggregate of atoms.
- the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 of the total volume ⁇ Vi 1.5 or more of the aggregate of atoms having a radius r G of 1.5 nm or more is 20 to 70%.
- each invention example is excellent in BH property even after the tempering treatment at room temperature after aging and at the low temperature and short time.
- Table 6 even after room temperature aging after the tempering treatment, the As yield strength is relatively low and the yield ratio is low, so it is excellent in press formability to automobile panels and the like. Also, heme workability is excellent.
- a low yield ratio press formability of 110 MPa or less and an As 0.2% yield strength of less than 0.50, and good bending workability can be exhibited. Therefore, it has both formability and baking coating curability, and can achieve both high BH property and low yield ratio.
- Comparative Examples 37 to 42, 44 to 47, 49 and 50 in Table 5 use the same alloy examples 24, 25 and 26 as the invention examples in Table 4. However, in each of these comparative examples, as shown in Table 5, the pre-aging treatment conditions are not preferable. As a result, the solid solution amount of Mg + Si, the average volume fraction ( ⁇ Vi / V Al ) ⁇ 100, or the average volume fraction ( ⁇ Vi 1.5 or more / ⁇ Vi) ⁇ 100 is within the range specified in this embodiment. It is off. As a result, compared with the invention example having the same alloy composition, the room temperature aging is large, and particularly the As yield strength after holding at room temperature for 30 days is relatively high or the yield ratio is high and low. It is inferior in press formability and hem workability, or inferior in BH property. Therefore, the moldability and the bake coating curability cannot be achieved, and the high BH property and the low yield ratio cannot be achieved at the same time.
- the temperature reached in the preliminary aging treatment is 130 ° C., which is too high, exceeding the upper limit of 120 ° C. For this reason, the amount of precipitation nuclei generated in the preliminary aging treatment is excessively increased, and the aggregate of relatively large size atoms contributing to the strength decreases, and the average volume fraction ( ⁇ Vi / V Al ) ⁇ 100 exceeds 1.5%, As proof strength is too high, and the yield ratio of the plate during forming cannot be lowered to less than 0.50.
- Comparative Examples 59 to 67 in Table 6 are manufactured within a preferable range including the pre-aging treatment conditions, but use Alloy Nos. 35 to 43 in Table 4, and contain Mg and Si as essential elements. Each amount is out of the range of the present embodiment, or the amount of impurity elements is too large. For this reason, as shown in Table 6, these comparative examples 59 to 67 have a too high As yield strength and yield ratio after being kept at room temperature for 30 days, as compared with the examples of the invention. Inferior to heme workability or BH property.
- the comparative example 59 is the alloy 35 of Table 4, and there is too little Si.
- the comparative example 60 is the alloy 36 of Table 4, and there is too much Si.
- Comparative example 61 is alloy 37 of Table 4, and there is too little Sn.
- the comparative example 62 is the alloy 38 of Table 4, and there was too much Sn, the crack was produced at the time of hot rolling, and the board was not able to be manufactured.
- the comparative example 63 is the alloy 39 of Table 4, and there is too much Fe.
- the comparative example 64 is the alloy 40 of Table 4, and there is too much Mn.
- the comparative example 65 is the alloy 41 of Table 4, and there are too many Cr and Ti.
- the comparative example 66 is the alloy 42 of Table 4, and there is too much Zn.
- Comparative example 67 is alloy 43 of Table 4, and there is too much Zr and V.
- the present invention it is possible to provide a 6000 series aluminum alloy plate having both BH properties and formability after aging at room temperature.
- the application of the 6000 series aluminum alloy plate can be expanded to automobile panels, in particular, outer panels where design properties such as beautiful curved surface configurations and character lines are problematic.
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Abstract
Description
このうち、特許文献1では、BH性や室温時効性に影響するクラスタ(原子の集合体)を、板の組織をそのまま直接的に、100万倍の透過型電子顕微鏡によって分析し、観察されるクラスタ(原子の集合体)の内、円等価直径が1~5nmの範囲のクラスタの平均数密度を一定の範囲で規定して、BH性に優れ、室温時効を抑制したものとしている。
但し、前記アルミニウム合金板の各測定箇所における示差熱分析においては、試験装置:セイコ-インスツルメンツ製DSC220G、標準物質:アルミニウム、試料容器:アルミニウム、昇温条件:15℃/min、雰囲気:アルゴン(50ml/min)、試料重量:24.5~26.5mgの同一条件で各々行い、得られた示差熱分析のプロファイル(μW)を試料重量で割って規格化した(μW/mg)後に、前記示差熱分析プロファイルでの0~100℃の区間において、示差熱分析のプロファイルが水平になる領域を0の基準レベルとし、この基準レベルからの発熱ピーク高さを測定する。
かつ、3次元アトムプローブ電界イオン顕微鏡により測定された原子の集合体として、Mg原子かSi原子かのいずれか又は両方を合計で10個以上含み、これらに含まれるMg原子かSi原子のいずれの原子を基準としても、その基準となる原子と隣り合う他の原子のうちのいずれかの原子との互いの距離が0.75nm以下である条件を満たす原子の集合体について、これらの原子集合体の総体積として、個々の原子の集合体を各々球と見なした際のギニエ半径rGから算出される個々の原子の集合体の体積Vi(=4/3πrG 3)を合計した総体積ΣViの、前記3次元アトムプローブ電界イオン顕微鏡により測定された前記アルミニウム合金板の体積VAlに占める平均体積分率(ΣVi/VAl)×100が0.3~1.5%の範囲であるとともに、
前記原子集合体の総体積ΣViのうち、前記ギニエ半径rGが1.5nm以上である原子の集合体の体積V1.5以上を合計した総体積ΣVi1.5以上の占める平均体積分率(ΣVi1.5以上/ΣVi)×100が20~70%である、
こととする。
以下に、本発明の第1の実施の形態につき、要件ごとに具体的に説明する。
先ず、本実施形態のAl-Mg-Si系(以下、6000系とも言う)アルミニウム合金板の化学成分組成について、以下に説明する。本実施形態が対象とする6000系アルミニウム合金板は、前記した自動車の外板用の板などとして、優れた成形性やBH性、強度、溶接性、耐食性などの諸特性が要求されるので、組成の面からもこれらの要求を満たすようにする。その上で、本実施形態では、Snを含有させて、製造後の板の室温時効を抑制して、パネル成形時の0.2%耐力を110MPa以下に低くして、自動車のパネル構造体の、特に面歪が問題となるような自動車パネルなどへの成形性を向上させる。それとともに、焼付け塗装硬化後の0.2%耐力を200MPa以上とすることを、組成の面から可能とする。
Siは、SiはMgとともに、塗装焼き付け処理などの人工時効処理時に、強度向上に寄与する時効析出物を形成して、時効硬化能を発揮し、自動車パネルとして必要な強度(耐力)を得るための必須の元素である。Si添加量が少なすぎると、人工時効後の析出量が少なくなりすぎ、焼付け塗装時の強度増加量が低くなりすぎてしまう。一方Si含有量が多すぎると、不純物のFeなどと粗大な晶出物を形成してしまい、曲げ加工性などの成形性を著しく低下させてしまう。また、Si含有量が多すぎると、板の製造直後の強度だけでなく、製造後の室温時効量も高くなり、成形前の強度が高くなりすぎて、自動車のパネル構造体の、特に面歪が問題となるような自動車パネルなどへの成形性が低下してしまう。したがって、Siの含有量は0.3~2.0%の範囲とする。
Mgも、Siとともに本実施形態で規定する前記クラスタ形成の重要元素であり、塗装焼き付け処理などの前記人工時効処理時に、Siとともに強度向上に寄与する時効析出物を形成して、時効硬化能を発揮し、パネルとしての必要耐力を得るための必須の元素である。Mg含有量が少なすぎると、人工時効後の析出量が少なくなりすぎ焼付け塗装後の強度が低くなりすぎてしまう。一方、Mg含有量が多くなりすぎると、不純物のFeなどと粗大な晶出物を形成してしまい、曲げ加工性などの成形性を著しく低下させてしまう。また、Mg含有量が高すぎると、板の製造直後の強度だけでなく、製造後の室温時効量も高くなり、成形前の強度が高くなりすぎて、自動車のパネル構造体の、特に面歪が問題となるような自動車パネルなどへの成形性が低下してしまう。したがって、Mgの含有量は0.2~2.0%の範囲とする。
Snは、室温においては、原子空孔を捕獲(捕捉、トラップ)することで、室温でのMgやSiの拡散を抑制し、室温における強度増加を抑制し、板のパネルへの成形時に、ヘム加工性や絞り加工や張出加工などのプレス成形性(以下、このプレス成形性を代表してヘム加工性とも言う)を向上させる効果がある。そして、パネルの塗装焼き付け処理などの人工時効処理時には捕獲していた空孔を放出するため、逆にMgやSiの拡散を促進し、BH性を高くすることができる。Sn含有量が0.005%よりも少ないと、十分に空孔をトラップしきれずにその効果を発揮できない。一方、Sn含有量が0.3%よりも多いと、Snが粒界に偏析し、粒界割れの原因となりやすい。なお、Sn含有量の好ましい下限値は0.01%である。Sn含有量の好ましい上限値は0.2%、さらには0.1%、より好ましくは0.06%である。
以上のような組成とした上で、本実施形態では、6000系アルミニウム合金板の組織について、自動車パネルなどとしての高強度を保証するために、焼付け塗装硬化処理後において析出する析出物の量を保証する目安として、この板のDSCにおいて、焼付け塗装前の強度および焼付け塗装時の強度増加に特に関わる、特定の温度範囲における吸熱ピークおよび発熱ピークを制御する。言い換えると、Snを添加しても、強度に寄与するMg-Siクラスタの減少や、焼付け塗装硬化処理後において析出する析出物量が不足しないように、この板のDSCを用いて、焼付け塗装前の強度および焼付け塗装時の強度増加に特に関わる、特定の温度範囲における吸熱ピークおよび発熱ピークを制御する。
具体的には、前記アルミニウム合金板の各測定箇所における示差熱分析においては、試験装置:セイコ-インスツルメンツ製DSC220G、標準物質:アルミニウム、試料容器:アルミニウム、昇温条件:15℃/min、雰囲気:アルゴン(50ml/min)、試料重量:24.5~26.5mgの同一条件で各々行い、得られた示差熱分析のプロファイル(μW)を試料重量で割って規格化した(μW/mg)後に、前記示差熱分析プロファイルでの0~100℃の区間において、示差熱分析のプロファイルが水平になる領域を0の基準レベルとし、この基準レベルからの発熱ピーク高さを測定する。
次に、本実施形態のアルミニウム合金板の製造方法について以下に説明する。本実施形態のアルミニウム合金板は、製造工程自体は常法あるいは公知の方法であり、上記6000系成分組成のアルミニウム合金鋳塊を鋳造後に均質化熱処理し、熱間圧延、冷間圧延が施されて所定の板厚とされ、更に溶体化焼入れなどの調質処理が施されて製造される。
先ず、溶解、鋳造工程では、上記6000系成分組成範囲内に溶解調整されたアルミニウム合金溶湯を、連続鋳造法、半連続鋳造法(DC鋳造法)等の通常の溶解鋳造法を適宜選択して鋳造する。ここで、鋳造時の平均冷却速度について、液相線温度から固相線温度までを30℃/分以上と、できるだけ大きく(速く)することが好ましい。
次いで、前記鋳造されたアルミニウム合金鋳塊に、熱間圧延に先立って、均質化熱処理を施す。この均質化熱処理(均熱処理)は、組織の均質化、すなわち、鋳塊組織中の結晶粒内の偏析をなくすことを目的とする。この目的を達成する条件であれば、特に限定されるものではなく、通常の1回または1段の処理でも良い。
熱間圧延は、圧延する板厚に応じて、鋳塊 (スラブ) の粗圧延工程と、仕上げ圧延工程とから構成される。これら粗圧延工程や仕上げ圧延工程では、リバース式あるいはタンデム式などの圧延機が適宜用いられる。
この熱延板の冷間圧延前の焼鈍 (荒鈍) は必ずしも必要ではないが、結晶粒の微細化や集合組織の適正化によって、成形性などの特性を更に向上させる為に実施しても良い。
冷間圧延では、上記熱延板を圧延して、所望の最終板厚の冷延板 (コイルも含む) に製作する。但し、結晶粒をより微細化させるためには、パス数に関わらず、合計の冷間圧延率は60%以上であることが望ましい。
冷間圧延後、溶体化処理と、これに続く、室温までの焼入れ処理を行う。この溶体化焼入れ処理については、通常の連続熱処理ラインによる加熱,冷却でよく、特に限定はされない。ただ、各元素の十分な固溶量を得ること、および前記した通り、結晶粒はより微細であることが望ましいことから、520℃以上、溶融温度以下の溶体化処理温度に、加熱速度5℃/秒以上で加熱して、0.1~10秒保持する条件で行うことが望ましい。
このような溶体化処理後に焼入れ処理して室温まで冷却した後、1時間以内に冷延板を予備時効処理(再加熱処理)する。室温までの焼入れ処理終了後、予備時効処理開始(加熱開始)までの室温保持時間が長すぎると、室温時効により溶解しやすいクラスタとして、前記した強度に寄与しない小さなMg-Siクラスタが多く生成してしまい、150~230℃の温度範囲の吸熱ピークのピーク高さを8μW/mg以下に抑制することが難しくなる。したがって、この室温保持時間は短いほど良く、溶体化および焼入れ処理と再加熱処理とが、時間差が殆ど無いように連続していても良く、下限の時間は特に設定しない。
先ず、本実施形態のAl-Mg-Si系(以下、6000系とも言う)アルミニウム合金板の化学成分組成について、以下に説明する。本実施形態が対象とする6000系アルミニウム合金板は、前記した自動車の外板用の板などとして、優れた成形性やBH性、強度、溶接性、耐食性などの諸特性が要求されるので、組成の面からもこれらの要求を満たすようにする。その上で、本実施形態では、Snを含有させて、製造後の板の室温時効を抑制して、パネル成形時の0.2%耐力を110MPa以下に低くするとともに、降伏比を0.50未満に低くして、自動車のパネル構造体の、特に面歪が問題となるような自動車パネルなどへの成形性を向上させる。それとともに、焼付け塗装硬化後の0.2%耐力を190MPa以上とすることを、組成の面から可能とする。
Siは、SiはMgとともに、塗装焼き付け処理などの人工時効処理時に、強度向上に寄与する時効析出物を形成して、時効硬化能を発揮し、自動車パネルとして必要な強度(耐力)を得るための必須の元素である。また、固溶Siは加工硬化能を向上させる元素であり、固溶することで引張強度と降伏強度の比(0.2%耐力/引張強度)である降伏比を0.50未満に低下させる効果がある。
Mgも、Siとともに本実施形態で規定する前記原子の集合体形成の重要元素であり、塗装焼き付け処理などの前記人工時効処理時に、Siとともに強度向上に寄与する時効析出物を形成して、時効硬化能を発揮し、パネルとしての必要耐力を得るための必須の元素である。また、Siと同じく、固溶Mgは加工硬化能を向上させる元素であり、固溶することで引張強度と降伏強度の比(0.2%耐力/引張強度)である降伏比を0.50未満に低下させる効果がある。
Snは、後述するMg+Siの固溶量を増しても、パネル成形時の0.2%耐力を増加させる原子集合体の体積分率を低くして、高BH性化と低降伏比化とを両立させる重要な効果がある。一般的に、Mg+Siの固溶量を増すためには、板に含有させるMgなりSiなりの量を増加させることが有効である。しかし、これらMgやSiの板の含有量を増加させると、パネル成形時の0.2%耐力を増加させ、かつ低降伏比化を阻害する原子集合体の体積分率も増加してしまうため、高BH性化と低耐力化と低降伏比化の両立は、従来の組成や製法では難しかった。これに対して、本実施形態は、Snを前記範囲で含有させることで、Mg+Siの固溶量を増してBH性を高めても、低降伏比化を阻害する原子集合体を抑制でき、高BH性化と低耐力化と低降伏比化とを両立させることができる。
以上のような組成とした上で、本実施形態では、BH性を高めるために、更に、板が含有するMgとSiとの合計の固溶量(Mg+Siの固溶量)を増加させ、1.0質量%以上、2.0質量%以下の一定の範囲で確保する。Mg+Siの固溶量が1.0質量%未満では、前記組成としてもBH性を確保できない。このMg+Siの固溶量が多いほどBH性が向上するが、MgとSiと含有量と固溶量には前記した組成や製造上の制約もあり、また固溶量が多すぎると、前記した原子集合体の体積分率が増加し、パネル製経時の耐力および降伏比が大きくなる問題もあり、上限は2.0質量%とする。
以上のような組成、組織とした上で、本実施形態では、更に、6000系アルミニウム合金板の組織について、降伏比を0.50未満に低くし、またBH性も保証するために、3次元アトムプローブ電界イオン顕微鏡により測定された、MgとSiとの原子の集合体のサイズ分布を制御する。これによって、前記したSnの効果だけでなく、板の組織中における原子集合体(クラスタ)を制御して、高BH性化と低降伏比化とを両立させる。
但し、効果の欄で記載した通り、本実施形態では、3次元アトムプローブ電界イオン顕微鏡の原理に基づく測定および解析によって規定される幾つかの条件(要件)を満たすものを、原子の集合体と定義している。すなわち、3次元アトムプローブ電界イオン顕微鏡により、高電界下で一旦イオン化(電界蒸発)された板の原子の、飛行時間と位置から解析されて再構築された、3次元の原子構造(3次元アトムマップ)において、本実施形態で規定する幾つかの条件(要件)を満たすものを、原子の集合体と定義している。
本実施形態において原子の集合体であると定義される(みなされる)ための条件(前提条件)を以下に説明する。
先ず、本実施形態では、以上説明した、Mg原子、Si原子の個数や原子間距離などの一定の条件を満たす原子集合体の総体積として、個々の原子の集合体を各々球と見なした際のギニエ半径rGから算出される個々の原子の集合体の体積Vi(=4/3πrG 3)を合計した総体積ΣViを求める。そして、この総体積ΣViの、前記3次元アトムプローブ電界イオン顕微鏡により測定された前記アルミニウム合金板の体積VAlに占める平均体分率(ΣVi/VAl)×100を0.3~1.5%の範囲に制御する。
3DAPの測定原理と測定方法も前記特許文献1~3によって公知である。すなわち、3DAP(3次元アトムプローブ)は、電界イオン顕微鏡(FIM)に、飛行時間型質量分析器を取り付けたものである。このような構成により、電界イオン顕微鏡で金属表面の個々の原子を観察し、飛行時間質量分析により、これらの原子を同定することのできる局所分析装置である。また、3DAPは、試料から放出される原子の種類と位置とを同時に分析可能であるため、原子の集合体の構造解析上、非常に有効な手段となる。このため、公知技術として、前記した通り、磁気記録膜や電子デバイスあるいは鋼材の組織分析などに使用されている。また、最近では、前記した通り、アルミニウム合金板の組織の原子の集合体の判別などにも使用されている。
これら3DAPによる原子の検出効率は、現在のところ、イオン化した原子のうちの50%程度が限界であり、残りの原子は検出できない。この3DAPによる原子の検出効率が、将来的に向上するなど、大きく変動すると、本実施形態が規定する各サイズの原子の集合体の平均個数密度(個/μm3)の3DAPによる測定結果が変動してくる可能性がある。したがって、この測定に再現性を持たせるためには、3DAPによる原子の検出効率は約50%と略一定にすることが好ましい。
次に、本実施形態のアルミニウム合金板の製造方法について以下に説明する。本実施形態のアルミニウム合金板は、製造工程自体は常法あるいは公知の方法であり、上記6000系成分組成のアルミニウム合金鋳塊を鋳造後に均質化熱処理し、熱間圧延、冷間圧延が施されて所定の板厚とされ、更に溶体化焼入れなどの調質処理が施されて製造される。
先ず、溶解、鋳造工程では、上記6000系成分組成範囲内に溶解調整されたアルミニウム合金溶湯を、連続鋳造法、半連続鋳造法(DC鋳造法)等の通常の溶解鋳造法を適宜選択して鋳造する。ここで、鋳造時の平均冷却速度について、液相線温度から固相線温度までを30℃/分以上と、できるだけ大きく(速く)することが好ましい。
次いで、前記鋳造されたアルミニウム合金鋳塊に、前記第1の実施形態の場合と同様に、均質化熱処理、熱間圧延、(必要に応じて)熱延板の焼鈍、冷間圧延、及び、溶体化および焼入れ処理の各処理を施す。なお、これら各処理の諸条件については前記第1の実施形態と同様であるため、ここでは説明を省略する。
このような溶体化処理後に焼入れ処理して室温まで冷却した後、1時間(60分)以内のできるだけ短時間内に、冷延板を予備時効処理(再加熱処理)する。
次に本発明の第1の実施形態に係る実施例を説明する。本実施形態でDSCで規定の組織が異なる6000系アルミニウム合金板を、溶体化および焼入れ処理後の予備時効処理の条件を変えて作り分けて製造した。そして、板製造後室温に30日間保持後の、BH性(塗装焼付け硬化性)、プレス成形性の指標としてのAs耐力や、曲げ加工性としてのヘム加工性を各々測定、評価した。
前記供試板の板厚中央部の10箇所における組織の前記DSCを測定し、これら10箇所の平均値にて、この板のDSC(示差走査熱分析曲線)において、強度に寄与しないMg-Siクラスタの溶解に相当する吸熱ピークとして、150~230℃の温度範囲の吸熱ピークのピーク高さ(W/mg)、強度に寄与するMg-Siクラスタの生成に相当する発熱ピークとして、240~255℃の温度範囲の発熱ピークのピーク高さ(μW/mg)を各々求めた。
前記調質処理後30日間室温放置した後の各供試板の機械的特性として、0.2%耐力(As耐力)を引張試験により求めた。また、これらの各供試板を各々共通して、30日間の室温時効させた後に、170℃×20分の人工時効硬化処理した後(BH後)の、供試板の0.2%耐力(BH後耐力)を引張試験により求めた。そして、これら0.2%耐力同士の差(耐力の増加量)から各供試板のBH性を評価した。
ヘム加工性は、前記調質処理後30日間室温放置後の各供試板についてのみ行った。試験は、30mm幅の短冊状試験片を用い、ダウンフランジによる内曲げR1.0mmの90°曲げ加工後、1.0mm厚のインナを挟み、折り曲げ部を更に内側に、順に約130度に折り曲げるプリヘム加工、180度折り曲げて端部をインナに密着させるフラットヘム加工を行った。
0;割れ、肌荒れ無し、1;軽度の肌荒れ、2;深い肌荒れ、3;微小表面割れ、4;線状に連続した表面割れ
比較例26は表1の合金14であり、Siが多すぎる。
比較例276は表1の合金15であり、Snが少なすぎる。
比較例28は表1の合金16であり、Snが多すぎ、熱延時に割れが生じて板の製造ができなかった。
比較例29は表1の合金17であり、Feが多すぎる。
比較例30は表1の合金18であり、Mnが多すぎる。
比較例31は表1の合金19であり、CrおよびTiが多すぎる。
比較例32は表1の合金20であり、Cuが多すぎる。
比較例33は表1の合金21であり、Znが多すぎる。
比較例34は表1の合金22であり、ZrおよびVが多すぎる。
前記した測定方法により、板のMg+Siの固溶量や3次元アトムプローブ電界イオン顕微鏡により測定された原子の集合体の各体積分率などを測定および解析して求めた。なお、表5、6では、3次元アトムプローブ電界イオン顕微鏡により測定された各原子の集合体の平均体積分率(%)を「3DAP測定原子の集合体の平均体積分率(%)と略記している。
前記調質処理後30日間室温放置した後の各供試板の機械的特性として、0.2%耐力(As耐力)を引張試験により求めた。また、これらの各供試板を各々共通して、30日間の室温時効させた後に、170℃×20分の人工時効硬化処理した後(BH後)の、供試板の0.2%耐力(BH後耐力)を引張試験により求めた。そして、これら0.2%耐力同士の差(耐力の増加量)から各供試板のBH性を評価した。
ヘム加工性は、前記調質処理後7日間または100日間室温放置後の各供試板についてのみ行った。試験は、30mm幅の短冊状試験片を用い、ダウンフランジによる内曲げR1.0mmの90°曲げ加工後、1.0mm厚のインナを挟み、折り曲げ部を更に内側に、順に約130度に折り曲げるプリヘム加工、180度折り曲げて端部をインナに密着させるフラットヘム加工を行った。
0;割れ、肌荒れ無し、1;軽度の肌荒れ、2;深い肌荒れ、3;微小表面割れ、4;線状に連続した表面割れ
比較例60は表4の合金36であり、Siが多すぎる。
比較例61は表4の合金37であり、Snが少なすぎる。
比較例62は表4の合金38であり、Snが多すぎ、熱延時に割れが生じて板の製造ができなかった。
比較例63は表4の合金39であり、Feが多すぎる。
比較例64は表4の合金40であり、Mnが多すぎる。
比較例65は表4の合金41であり、CrおよびTiが多すぎる。
比較例66は表4の合金42であり、Znが多すぎる。
比較例67は表4の合金43であり、ZrおよびVが多すぎる。
なお、本出願は、2014年3月31日付けで出願された日本特許出願(特願2014-074045)及び2014年3月31日付けで出願された日本特許出願(特願2014-074046)に基づいており、その全体が引用により援用される。
Claims (4)
- 質量%で、Mg:0.2~2.0%、Si:0.3~2.0%、Sn:0.005~0.3%を各々含み、残部がAlおよび不可避的不純物からなるAl-Mg-Si系アルミニウム合金板であって、前記アルミニウム合金板の示差走査熱分析曲線において、Mg-Siクラスタの溶解に相当する吸熱ピークとして、150~230℃の温度範囲の吸熱ピークのピーク高さが8μW/mg以下(但し、0μW/mgを含む)である一方で、Mg-Siクラスタの生成に相当する発熱ピークとして、240~255℃の温度範囲の発熱ピークのピーク高さが20μW/mg以上であることを特徴とする成形性と焼付け塗装硬化性とに優れたアルミニウム合金板。
- 前記アルミニウム合金板が、更に、Fe:0%超1.0%以下、Mn:0%超1.0%以下、Cr:0%超0.3%以下、Zr:0%超0.3%以下、V:0%超0.3%以下、Ti:0%超0.1%以下、Cu:0%超1.0%以下、Ag:0%超0.2%以下、及び、Zn:0%超1.0%以下からなる群より選ばれる1種または2種以上を含む請求項1に記載の成形性と焼付け塗装硬化性とに優れたアルミニウム合金板。
- 質量%で、Mg:0.3~1.0%、Si:0.5~1.5%、Sn:0.005~0.3%を各々含み、残部がAlおよび不可避的不純物からなるAl-Mg-Si系アルミニウム合金板であって、熱フェノールによる残渣抽出法により分離された溶液中のMg+Siの固溶量が、1.0質量%以上、2.0質量%以下であり、
かつ、3次元アトムプローブ電界イオン顕微鏡により測定された原子の集合体として、Mg原子かSi原子かのいずれか又は両方を合計で10個以上含み、これらに含まれるMg原子かSi原子のいずれの原子を基準としても、その基準となる原子と隣り合う他の原子のうちのいずれかの原子との互いの距離が0.75nm以下である条件を満たす原子の集合体について、
これらの原子集合体の総体積として、個々の原子の集合体を各々球と見なした際のギニエ半径rGから算出される個々の原子の集合体の体積Vi(=4/3πrG 3)を合計した総体積ΣViの、前記3次元アトムプローブ電界イオン顕微鏡により測定された前記アルミニウム合金板の体積VAlに占める平均体積分率(ΣVi/VAl)×100が0.3~1.5%の範囲であるとともに、
前記原子集合体の総体積ΣViのうち、前記ギニエ半径rGが1.5nm以上である原子の集合体の体積V1.5以上を合計した総体積ΣVi1.5以上の占める平均体積分率(ΣVi1.5以上/ΣVi)×100が20~70%である、
ことを特徴とする成形性と焼付け塗装硬化性とに優れたアルミニウム合金板。 - 前記アルミニウム合金板が、更に、Fe:0%超1.0%以下、Mn:0%超0.4%以下、Cr:0%超0.3%以下、Zr:0%超0.3%以下、V:0%超0.3%以下、Ti:0%超0.1%以下、Cu:0%超0.4%以下、Ag:0%超0.2%以下、及び、Zn:0%超1.0%以下からなる群より選ばれる1種または2種以上を含む請求項3に記載の成形性と焼付け塗装硬化性とに優れたアルミニウム合金板。
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US10513766B2 (en) | 2015-12-18 | 2019-12-24 | Novelis Inc. | High strength 6XXX aluminum alloys and methods of making the same |
US10538834B2 (en) | 2015-12-18 | 2020-01-21 | Novelis Inc. | High-strength 6XXX aluminum alloys and methods of making the same |
US11932928B2 (en) | 2018-05-15 | 2024-03-19 | Novelis Inc. | High strength 6xxx and 7xxx aluminum alloys and methods of making the same |
FR3142767A1 (fr) | 2022-12-05 | 2024-06-07 | Constellium Neuf-Brisach | ALLIAGE d’ALUMINIUM 6XXX AVEC RECYCLABILITE AMELIOREE |
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WO2018183721A1 (en) | 2017-03-30 | 2018-10-04 | NanoAL LLC | High-performance 6000-series aluminum alloy structures |
ES2964962T3 (es) | 2019-03-13 | 2024-04-10 | Novelis Inc | Aleaciones de aluminio endurecibles por envejecimiento y altamente conformables, chapa monolítica y productos de aleación de aluminio revestidos que la contengan |
CN110835686B (zh) * | 2019-11-29 | 2021-03-19 | 北京科技大学 | 一种铂族金属捕集剂及铂族金属回收方法 |
CN112941378B (zh) * | 2021-01-25 | 2022-06-07 | 广东澳美铝业有限公司 | 一种慢速自然时效6系铝合金 |
CN114921697B (zh) * | 2022-07-20 | 2022-09-30 | 中铝材料应用研究院有限公司 | 发动机盖内板用6xxx系铝合金板材、其制备方法及应用 |
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Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US10513766B2 (en) | 2015-12-18 | 2019-12-24 | Novelis Inc. | High strength 6XXX aluminum alloys and methods of making the same |
US10538834B2 (en) | 2015-12-18 | 2020-01-21 | Novelis Inc. | High-strength 6XXX aluminum alloys and methods of making the same |
US11920229B2 (en) | 2015-12-18 | 2024-03-05 | Novelis Inc. | High strength 6XXX aluminum alloys and methods of making the same |
US11932928B2 (en) | 2018-05-15 | 2024-03-19 | Novelis Inc. | High strength 6xxx and 7xxx aluminum alloys and methods of making the same |
FR3142767A1 (fr) | 2022-12-05 | 2024-06-07 | Constellium Neuf-Brisach | ALLIAGE d’ALUMINIUM 6XXX AVEC RECYCLABILITE AMELIOREE |
WO2024121494A1 (fr) | 2022-12-05 | 2024-06-13 | Constellium Neuf-Brisach | Alliage d'aluminium 6xxx avec recyclabilite amelioree |
Also Published As
Publication number | Publication date |
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MX2016012707A (es) | 2016-12-16 |
KR20160127112A (ko) | 2016-11-02 |
CN106103763A (zh) | 2016-11-09 |
KR101850234B1 (ko) | 2018-04-18 |
US20190010581A1 (en) | 2019-01-10 |
CA2941988A1 (en) | 2015-10-08 |
US20170175231A1 (en) | 2017-06-22 |
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