CN110461528B - Method for manufacturing resistance spot-welded joint - Google Patents

Method for manufacturing resistance spot-welded joint Download PDF

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CN110461528B
CN110461528B CN201880021920.8A CN201880021920A CN110461528B CN 110461528 B CN110461528 B CN 110461528B CN 201880021920 A CN201880021920 A CN 201880021920A CN 110461528 B CN110461528 B CN 110461528B
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energization
plate
electrode
resistance spot
steel plate
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CN110461528A (en
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泽西央海
松田广志
池田伦正
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JFE Steel Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/10—Spot welding; Stitch welding
    • B23K11/11—Spot welding
    • B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/10—Spot welding; Stitch welding
    • B23K11/11—Spot welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
    • B23K11/18—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded of non-ferrous metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
    • B23K11/20—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded of different metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/30—Features relating to electrodes

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  • Mechanical Engineering (AREA)
  • Resistance Welding (AREA)

Abstract

The resistance spot welding joint is manufactured by overlapping at least one steel plate selected from a plated steel plate, a cold-rolled steel plate and a hot-rolled steel plate with an aluminum plate, wherein one of the outermost plates is the steel plate and the other is the aluminum plate1(kA) at energization time t1A first energization step of energizing for a period (ms), and an energization suspension time t after the first energization stepcAn energization stopping step of stopping energization in a period (ms) and a step of applying a current I after the energization stopping step2(kA) at energization time t2A second energization step of energizing for a period of (ms) to set the total thickness of the stacked steel sheets to TFe(mm) R is the radius of curvature of the tip of the electrode in contact with the steel plateFe(mm) the diameter of the tip of the electrode in contact with the steel plate is DFe(mm) satisfies all of the formulae (1) to (6). I is1＜I2(1)、t1＞t2(2)、t1≥40(3)、tc≥5(4)、
Figure DDA0002217812130000011
RFe≥20(6)。

Description

Method for manufacturing resistance spot-welded joint
Technical Field
The present invention relates to a method for manufacturing a resistance spot-welded joint of dissimilar metal materials. More specifically, the present invention relates to a method for manufacturing a resistance spot weld joint, in which a plate group formed by stacking at least one steel sheet selected from a plated steel sheet, a cold-rolled steel sheet, and a hot-rolled steel sheet on an aluminum sheet is joined by resistance spot welding to manufacture a resistance spot weld joint.
Background
In the automobile industry in recent years, application of light metals such as aluminum alloys to vehicle bodies has been advanced for the purpose of improving fuel efficiency by weight reduction of the vehicle bodies. At present, resistance spot welding, which is superior in cost and efficiency compared to other welding methods, is used at most for joining steel plates to each other in a vehicle body, and the number of welding spots per vehicle reaches 3000 to 6000. Resistance spot welding is a method of joining two or more steel plates that are stacked together by resistance heating by applying pressure from the top and bottom of the steel plates by a pair of electrodes and applying a high-current welding current between the top and bottom electrodes in a short time.
From the viewpoint of maintaining the cost and efficiency of the production process of the vehicle body, it is effective to use resistance spot welding in the joining in the case where the aluminum plate is mixedly present, as in the joining in the case where the steel plates are joined to each other. In the following description, the aluminum plate is a generic name of a pure aluminum plate and an aluminum alloy plate. However, the joining of dissimilar metal materials of steel and aluminum has the following problems: since the pressing of the electrodes causes the thickness of the soft aluminum plate to be greatly reduced or a brittle intermetallic compound to be formed at the bonding interface, the joint strength, particularly the peel strength when a load in the peeling direction is generated as typified by cross-stretching, cannot be secured.
In order to solve the above-described problems, the following resistance spot welding method is proposed. For example, patent document 1 describes a resistance spot welding method in which an iron/aluminum composite thin plate is inserted between a steel plate and an aluminum plate so that the same materials face each other, thereby obtaining a high-strength joint even at a low current.
Patent document 2 describes a resistance spot welding method in which welding is performed by adding one or more backing plates to both sides of a steel sheet and an aluminum sheet, so that resistance heat is generated at the interface between the backing plates and the materials to be joined, and the steel and the aluminum are resistance diffusion joined, thereby obtaining a high-strength joint.
Patent document 3 describes: in spot welding of steel or aluminum material, the amounts of Mn and Si in the oxide film on the surface of steel sheet or steel sheet are optimized, whereby it is possible to obtain a large nugget diameter and suppress the occurrence of spattering.
Patent document 4 describes a dissimilar metal joining method in which the conditions of pulse energization are optimized and the pressurizing force after completion of energization is increased to suppress the growth of intermetallic compounds at the joining interface.
Patent document 5 describes a spot welding method in which the conditions of pre-energization and subsequent energization are optimized to suppress the occurrence of spatters from the surface of the steel sheet and to reduce the welding current as much as possible, thereby obtaining a dissimilar material joint having high joint strength.
Documents of the prior art
Patent document
Patent document 1: japanese patent No. 3117053
Patent document 2: japanese patent No. 3504790
Patent document 3: japanese patent laid-open publication No. 2005-152958
Patent document 4: japanese patent No. 5624901
Patent document 5: japanese patent No. 5572046
Disclosure of Invention
Problems to be solved by the invention
However, the resistance spot welding methods described in patent documents 1 and 2 have a problem that they require the use of a backing plate or a composite thin plate which is structurally unnecessary for a vehicle body, and therefore, they cause a significant increase in cost and fail to sufficiently reduce the weight.
In addition, in patent document 3, since the amount and distribution of the alloying elements in the steel sheet and the oxide film need to be limited, there is a problem that the use of the steel sheet satisfying the required performance is limited. Particularly, under the situation that high alloying accompanied by recent increase in strength of steel sheet is progressing, the application of the invention of patent document 3 is extremely limited.
In patent document 4, the energization time of the pre-energization is 20ms or less, and the energization time of the pulse energization is 10ms or less, both being short, and both the pre-energization and the pulse energization are required to be highly electrified in order to enlarge the joint diameter. Therefore, when the resistivity of the steel sheet is high and the sheet thickness is large, there is a concern that spatter may occur on the surface of the steel sheet.
Patent document 5 has a problem that the applicable plate group is limited to the plate group of cold-rolled steel sheets and 6000 series aluminum alloy sheets. Further, in patent document 5, although it is necessary to perform pre-energization under conditions that do not melt the aluminum alloy sheet, the aluminum alloy sheet has a lower melting point than the steel sheet, and therefore, there is a problem that the range of suitable conditions for pre-energization according to the plate group is very narrow.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a resistance spot weld joint capable of manufacturing a resistance spot weld joint of a steel plate and an aluminum plate having a good peel strength between the steel plate and the aluminum plate regardless of the components of the steel plate and the aluminum plate and the plate group.
Means for solving the problems
The present inventors have made extensive studies to achieve the above object, and as a result, have obtained the following findings. Fig. 1 is a diagram schematically showing a current distribution in an initial stage of energization in resistance spot welding. In fig. 1, the distribution of current (welding current) when a plate assembly formed by stacking a steel plate 11 and an aluminum plate 12 is sandwiched between a pair of electrodes 13 and 14 and energized while being pressurized is shown by reference numeral 21 in fig. 1.
In order to obtain a good peel strength in resistance spot welding of a steel sheet and an aluminum sheet, it is important to obtain a joint diameter (nugget diameter) as large as possible in order to reduce stress applied to the joint portion and to suppress the growth of brittle intermetallic compounds at the joint interface (contact surface between the steel sheet and the aluminum sheet). In general, it is effective to increase the welding current and the energization time in order to increase the joint diameter, but when the welding current and the energization time are increased, the linear energy increases, and intermetallic compounds easily grow at the joint interface. For the above reasons, it is difficult to provide a resistance spot welded joint between a steel sheet and an aluminum sheet with good peel strength (ensuring of peel strength).
Therefore, the present inventors have studied a welding condition such as an energization pattern and an electrode that can achieve both an increase in the joint diameter and a reduction in the wire energy. In resistance spot welding of a steel sheet and an aluminum sheet, generally, a steel sheet having a high resistivity first generates heat, and the aluminum sheet is melted by the heat transferred from the steel sheet to achieve joining. Therefore, the present inventors considered that it is important to heat a wide range of steel sheets in a short time in order to achieve both the increase in the joint diameter and the reduction in the wire energy.
When the line energy is reduced in order to suppress the growth of the intermetallic compound, it is effective to shorten the time until the junction interface reaches a high temperature state. Therefore, it is effective to set the energization mode to a short time and a high current, but since a strong oxide film is present on the surface of the aluminum plate, the energization path is limited, and as shown in fig. 1, the current is likely to concentrate at the center of the joint where the oxide film is broken by pressurization in the initial stage of energization. Therefore, excessive shortening of the time and increase in the current increase the line energy to the center of the joint, and therefore, there is a limit to shortening the energization time and increasing the current.
The present invention has been completed based on these findings and further research, and the gist thereof is as follows.
[1] A method for manufacturing a resistance spot weld joint by joining a plate group, which is formed by stacking at least one steel plate selected from a plated steel plate, a cold-rolled steel plate and a hot-rolled steel plate on an aluminum plate and by sandwiching one of the outermost plates as the steel plate and the other as the aluminum plate between a pair of electrodes, by resistance spot welding, the method comprising:
with a current I1(kA) at energization time t1A first energization step of energizing for a period (ms);
after the first energization step, at an energization suspension time tcAn energization suspending step of suspending energization for a period (ms); and
after the power-on stopping process, the current I is used2(kA) at energization time t2A second energization step of energizing for a period (ms),
the total thickness of the laminated steel plates is set to TFe(mm) R is the radius of curvature of the tip of the electrode in contact with the steel plateFe(mm) the diameter of the tip of the electrode in contact with the steel plate is DFe(mm) in the length of the groove,
the first energization step, the energization suspension step, and the second energization step satisfy all of the relationships of the following expressions (1) to (6).
I1＜I2 (1)
t1＞t2 (2)
t1≥40 (3)
tc≥5 (4)
Figure BDA0002217812110000051
RFe≥20 (6)
[2] The method of manufacturing a resistance spot welded joint according to [1], wherein the first energization step, the energization suspension step, and the second energization step further satisfy a relationship of the following expression (7).
RFe≥50 (7)
[3]Such as [1]]Or [2]]The method of manufacturing a resistance spot welded joint, wherein a radius of curvature of a tip of the electrode in contact with the aluminum plate is RAl(mm), the first energization step, the energization suspension step, and the second energization step further satisfy the relationship of the following expression (8).
RAl≥50 (8)
[4] The method of manufacturing a resistance spot weld joint according to any one of [1] to [3], wherein in the first energization step, at least a portion of the aluminum plate with which the electrode is in contact is melted.
Effects of the invention
According to the present invention, a resistance spot weld joint of a steel sheet and an aluminum sheet having good peel strength regardless of the composition of the steel sheet and the aluminum sheet and the plate group can be manufactured.
Drawings
Fig. 1 is a diagram schematically showing a current distribution in an initial stage of energization in resistance spot welding.
Fig. 2 is a view schematically showing resistance spot welding.
Fig. 3 is a diagram illustrating an energization pattern.
Fig. 4 is a diagram schematically showing a current distribution at the time of energization in the second energization step.
Fig. 5 is a view showing the radius of curvature of the tip and the diameter of the tip of the electrode.
Detailed Description
In the method for manufacturing a resistance spot weld joint according to the present invention, when a resistance spot weld joint is manufactured by joining a plate group, in which at least one steel sheet selected from the group consisting of a cold-rolled steel sheet, a hot-rolled steel sheet, and a plated steel sheet is laminated with an aluminum sheet and one of the outermost sheets is a steel sheet and the other is an aluminum sheet, by resistance spot welding with a pair of electrodes, the method includes: with a current I1(kA) at energization time t1A first energization step of energizing for a period (ms), and an energization suspension time t after the first energization stepcAn energization stopping step of stopping energization in a period (ms) and a step of applying a current I after the energization stopping step2(kA) at energization time t2A second energization step of energizing for a period of (ms) to set the total thickness of the stacked steel sheets to TFe(mm) R is the radius of curvature of the tip of the electrode in contact with the steel plateFe(mm) the diameter of the tip of the electrode in contact with the steel plate is DFe(mm), the first energization step, the energization suspension step and the second energization step satisfy all of the relationships of the following expressions (1) to (6). In the present invention, the resistance spot welded joint is a generic term including a test piece used for a strength test, a cross-sectional observation, and the like, an automobile member joined by resistance spot welding, and the like.
I1＜I2 (1)
t1＞t2 (2)
t1≥40 (3)
tc≥5 (4)
Figure BDA0002217812110000061
RFe≥20 (6)
The present invention will be specifically described below with reference to fig. 2 to 4. Fig. 2 is a view schematically showing resistance spot welding. Fig. 3 is a diagram illustrating an energization pattern. Fig. 4 is a diagram schematically showing a current distribution at the time of energization in the second energization step. The present invention relates to a method for manufacturing a resistance spot welded joint, in which a resistance spot welded joint is obtained by resistance spot welding in which a plate group formed by stacking a plurality of plates is sandwiched between a pair of electrodes and is joined (welded) by applying current while applying pressure.
First, a steel plate 11 and an aluminum plate 12 are laminated to form a plate assembly. At this time, as shown in fig. 2, one of the outermost plates is a steel plate 11 and the other is an aluminum plate 12. In other words, the plates in contact with the electrodes 13 and 14 are stacked so as to be the steel plate 11 and the aluminum plate 12, respectively. Fig. 2 shows an example of the resistance spot weld joint of a double-layer plate group in which the steel plate 11 and the aluminum plate 12 are stacked one on another, but a plate group of three or more layers in which one or more steel plates or aluminum plates are further sandwiched between the steel plate 11 and the aluminum plate 12 may be used.
In the present invention, the sheet constituting the resistance spot welding joint, i.e., the sheet subjected to resistance spot welding is at least one steel sheet selected from the group consisting of a plated steel sheet, a cold-rolled steel sheet and a hot-rolled steel sheet, and an aluminum sheet. The plated steel sheet is a steel sheet having a metal plating layer on the surface thereof, and examples of the metal plating layer include a Zn-based plating layer and an Al-based plating layer. Examples of the Zn-based plating layer include a general hot dip zinc plating layer (GI), an alloyed hot dip zinc plating layer (GA), an electrogalvanized zinc plating layer (EG), a Zn — Ni-based plating layer (for example, a Zn — Ni-based plating layer containing 10 to 25 mass% of Ni), a Zn — Al-based plating layer, a Zn — Mg-based plating layer, and a Zn — Al-Mg-based plating layer. Further, examples of the Al-based plating layer include an Al-Si-based plating layer (for example, an Al-Si-based plating layer containing 10 to 20 mass% of Si) and the like. The composition of the steel sheet 11 is not particularly limited. The strength of the steel sheet 11 is not particularly limited, and for example, a tensile test piece No. JIS5 is prepared from a steel sheet in a direction parallel to the rolling direction, and the tensile test piece is measured in accordance with JIS Z2241: 2011 specifies a steel sheet having a tensile strength of 270 to 1800MPa (270 to 1800 MPa) obtained by performing a tensile test. The composition of the aluminum plate is not particularly limited, and may be a pure aluminum plate or an aluminum alloy plate. Examples of the aluminum alloy sheet include 5000 series (Al-Mg series), 6000 series (Al-Mg-Si series), 2000 series (Al-Cu series), 7000 series (Al-Zn-Mg series, Al-Zn-Mg-Cu series) and the like specified in JIS. An oxide film was formed on the surface of the aluminum plate. The thicknesses of the steel sheet 11 and the aluminum sheet 12 are not particularly limited, and are preferably within a range (about 0.5mm to about 4.0mm) that can be used for a normal automobile body.
Next, a plate group formed by stacking the steel plate 11 and the aluminum plate 12 is sandwiched between a pair of welding electrodes (electrode 13 and electrode 14), and after applying a current while applying pressure, the electrodes are released from the steel plate. As a welding apparatus usable in the resistance spot welding method of the present invention, a welding apparatus which includes a pair of upper and lower electrodes and can arbitrarily control a pressurizing force and a welding current during welding can be used. The pressurizing mechanism (cylinder, servo motor, etc.) and the form (fixed type, robot welding gun, etc.) of the welding apparatus are not particularly limited. The present invention can be applied to any of dc and ac, and the type of power source (single-phase ac, ac inverter, dc inverter) and the like are not particularly limited. Here, in the case of alternating current, "current" means "effective current". The resistance spot welding was performed in a state of being constantly water-cooled.
In this way, the steel plate 11 and the aluminum plate 12 are stacked so that one of the outermost plates is the steel plate 11 and the other is the aluminum plate 12 to form a plate group. The plate group was sandwiched between a pair of welding electrodes (electrode 13 and electrode 14), and current was applied while applying pressure to form nuggets by resistance heating, and the laminated steel plate 11 and aluminum plate 12 were joined together to obtain a resistance spot welding joint.
In the present invention, the energization is set to a specific mode. That is, the current supply mode of the present invention has a current I as shown in FIG. 31(kA) at energization time t1A first energization step of energizing for a period of (ms), and a step of stopping energization after the first energization stepTime tcAn energization stopping step of stopping energization in a period (ms) and a step of applying a current I after the energization stopping step2(kA) at energization time t2A second energization step of energizing for a period of (ms) to set the total thickness of the stacked steel sheets to TFe(mm) R is the radius of curvature of the tip of the electrode 13 in contact with the steel plateFe(mm) the diameter of the tip of the electrode 13 in contact with the steel plate is DFe(mm) satisfies all the relationships of the above-mentioned equations (1) to (5). After the second energization step is completed, energization is performed in one or more stages as necessary, and then, for example, energization is performed in a third stage or later for the purpose of heat treatment or the like, and then, energization is stopped.
As described above, at the initial stage of energization, the energization path is restricted by the oxide film on the surface of the aluminum plate 12. Therefore, in the present invention, first, in the first energization step (first-stage energization), energization is performed for a longer time and at a lower current than in the second energization step (see the above-described equations (1) and (2)). This ensures a current path between the steel sheet 11 and the aluminum sheet 12 by breaking the oxide film on the surface of the aluminum sheet 12, and prevents an excessive increase in the amount of heat input. Further, the first energization step is performed for an energization time t1The electric path between the steel plate 11 and the aluminum plate 12 can be sufficiently secured by setting the electric path to 40ms or more (see the above expression (3)).
Then, after the first energization step, at a predetermined energization-off time tcThe energization is suspended for a period (ms) (energization suspending step), and after the energization suspending step, energization is performed in a second energization step (second-stage energization) for a shorter time and at a higher current than in the first energization step. This enables instantaneous heat generation over a wide range. Fig. 4 is a diagram schematically showing a current distribution at the time of energization in the second energization step. As shown in fig. 4, since the current density is high in the vicinity 22 of the contact end between the steel plate 11 and the electrode 13, the heat generation in the vicinity 22 of the contact end is promoted as the current becomes higher. Therefore, the increase in current in the second energization step is effective for generating heat over a wide range by short-time energization, and the joining diameter can be enlarged by melting the aluminum plate 12 over a wide range. However, in the first placeAt the end of energization in the energization step, the center of the joint where the oxide film is initially broken and energization is started in the first energization step becomes higher in temperature. Therefore, the energization-suspended time t in the energization-suspended stepcIn short, even if the energization in the second energization step is set to a short time and high current, the temperature rises again from the center of the high-temperature joint portion, and therefore, the linear energy tends to become excessively large.
Therefore, in the present invention, the energization-suspended time t is performedcAfter the energization suspending step for 5ms or longer (see the above equation (4)) and satisfying the above equation (5), a second energization step is performed at a high current for a short time. Accordingly, the temperature at the center of the joint portion is temporarily lowered in the energization suspending step, and therefore, heat generation in the vicinity 22 of the contact end between the steel sheet 11 and the electrode 13 having a high current density can be promoted in the energization of the second energization step, and the nugget diameter can be enlarged while suppressing the linear energy. Here, tcThe lower limit value of (b) is set based on the amount of heat generation in the first energization step and the amount of heat radiation to the electrode after the first energization step is completed. Thus, as tcThe lower limit value of (1) is determined by a parameter I affecting the above-mentioned heat generation amount and heat dissipation amount1、t1、TFe、DFeThe structural relation (5) (i.e., the left side of the above-mentioned formula (5)). T isFeIf the amount of heat generated by the steel sheet in the first energization step is large, the heat dissipation to the electrodes is difficult to occur, and therefore t iscThe lower limit value of (b) increases. In addition, DFeWhen it is large, the contact area with the electrode increases, whereby heat dissipation to the electrode is promoted, and therefore, tcThe lower limit value of (b) is decreased. In addition, tcThe excessive increase of (b) may lower the production efficiency, and therefore, with respect to tcThe upper limit value of (b) is also set in the relational expression (5) composed of the same parameters (i.e., the right side of the above expression (5)). In the second energization step, the energization time t2For example, it is preferably 5 to 100 ms.
In the present invention, in addition to the specific energization mode, the above-described expression (6) must be satisfied, that is, the radius of curvature R of the tip end is usedFeAn electrode having a thickness of 20mm or more is used as the electrode 13 in contact with the steel sheet 11. This is achieved byThis is because the radius of curvature R of the tip of the electrode 13 passing through the contact with the steel plate 11FeThe enlargement of (2) increases the contact area between the steel plate 11 and the electrode 13, thereby increasing the current-carrying area in the second current-carrying step, and expanding the heat generation range and the joint diameter of the steel plate 11. Further, by increasing the contact area between the steel plate 11 and the electrode 13, heat dissipation to the electrode 13 is promoted, and the energization-suspended time t after the end of the first energization step can be shortenedc. Further, by preventing an excessive increase in the current density in the vicinity 22 of the contact end between the steel plate 11 and the electrode 13, the effect of suppressing the occurrence of spatters from the surface of the steel plate can also be obtained. It is preferable to use the radius of curvature R of the tip of the electrode 13 in contact with the steel sheet 11FeA relation satisfying the following expression (7), that is, a radius of curvature R of the tipFeIs an electrode having a thickness of 50mm or more. The reason for this is to suppress surface splash by enlarging the contact area between the electrode and the steel sheet and reducing the current density.
RFe≥50 (7)
The form of the tip of the electrode 13 is, for example, JIS C9304: the DR (dome spherical), R (spherical) and D (dome) shapes described in 1999. The front end radius of curvature R and the front end diameter D of the electrode are shown in fig. 5. Fig. 5(a) is a view showing the radius of curvature R and the tip diameter D of the tip of the spherical electrode, and fig. 5(b) is a view showing the radius of curvature R and the tip diameter D of the tip of the dome-spherical electrode. As shown in fig. 5(b), the curved surface on the tip side of the dome-spherical electrode has a two-step curvature, and the radius of curvature of the tip of the electrode is the radius of curvature R of the portion (central curved surface) that first comes into contact with the plate to be resistance spot welded.
The diameter D of the tip of the electrode 13 in contact with the steel plate 11 is set so as to secure the contact area between the electrode and the steel plateFeFor example, preferably 4mm to 16 mm. Front end diameter D of electrode 13FeMore preferably 6mm to 16mm, and still more preferably 8mm to 16 mm.
In the present invention, by performing the above-described specific energization pattern and using a specific electrode as the electrode 13 in contact with the steel sheet 11, the aluminum sheet 12 can be melted over a wide range and excessive heat generation can be prevented, and therefore, the growth inhibition of intermetallic compounds at the joint interface due to the increase in the joint diameter and the reduction in the linear energy can be achieved at the same time. Therefore, in the present invention, the resistance spot weld joint of the steel plate 11 and the aluminum plate 12 having good peel strength can be manufactured. As described above, the composition and the plate group of the steel sheet and the aluminum sheet, specifically, the presence or absence and the thickness of the metal plating layer on the surface of the steel sheet and the aluminum sheet, the composition and the thickness of the oxide film, the base material strength, and the plate thickness can be applied.
It is preferable that the electrode 14 in contact with the aluminum plate 12 is set such that the radius of curvature of the tip of the electrode 14 in contact with the aluminum plate 12 is RAl(mm) satisfies the following formula (8), i.e., radius of curvature R of tipAlIs an electrode having a thickness of 50mm or more. This makes it possible to more effectively obtain the effects of the present invention. This is because, by reducing the surface pressure applied to the aluminum plate 12, an effect of suppressing a reduction in thickness of the aluminum plate 12 caused by energization can be obtained.
RAl≥50 (8)
The radius of curvature R of the tipAlMore preferably 80mm or more.
The form of the tip of the electrode 14 in contact with the aluminum plate 12 is, for example, JIS C9304: the DR (dome spherical), R (spherical) and D (dome) shapes described in 1999. From the viewpoint of reducing the surface pressure applied to the aluminum alloy sheet, the diameter D of the tip of the electrode 14 in contact with the aluminum sheet 12AlFor example, preferably 4mm to 16 mm. Front end diameter D of electrode 14AlMore preferably 6mm to 16mm, and still more preferably 8mm to 16 mm.
Further, the diameter D of the tip of the electrode 14 on the aluminum plate 12 sideAlThe diameter D of the tip of the electrode 13 on the steel plate 11 sideFeThe relationship of (a) and (b) is not particularly limited, and they may be the same or different.
In the present invention, when it is desired to widen the current range applicable to the energization in the second energization step, it is effective to secure a sufficient energization path between the steel sheet 11 and the aluminum sheet 12 in the first energization step. Therefore, the energization time t of the first energization step1Preferably 50ms or more, and more preferably 60ms or more. Energization time t of first energization step1The upper limit of (d) is not particularly limited, and the energization time t is preferably set from the viewpoint of shortening the tact time1Is 600ms or less.
In addition, at least a portion of the aluminum plate 12 is preferably melted at the time of energization in the first energization step. By melting the aluminum plate 12 at the time of energization in the first energization step, the oxide film on the surface of the aluminum plate 12 is completely removed, and therefore, stabilization of the energization path becomes possible. However, in order to prevent the linear energy from becoming excessively large, when the plate thickness of the aluminum plate 12 positioned outermost and in contact with the electrode 14 is t (mm), the nugget diameter of the outermost aluminum plate 12 in contact with the electrode 14 formed during energization in the first energization step is preferably set to be t (mm)
Figure BDA0002217812110000121
Hereinafter, it is more preferable that
Figure BDA0002217812110000122
The following. The nugget diameter of the outermost aluminum sheet 12 that is formed during the energization in the first energization step and that is in contact with the electrode 14 is preferably set to be the same as the nugget diameter of the outermost aluminum sheet 12
Figure BDA0002217812110000123
The above. The thickness T of the aluminum plate 12 is mm, and T is substituted
Figure BDA0002217812110000124
And
Figure BDA0002217812110000125
is also in mm. Here, the nugget diameter of the aluminum plate 12 is the maximum diameter of the nugget of the aluminum plate 12 in the contact surface (joint surface) between the aluminum plate 12 and the plate (steel plate 11 in fig. 2) in contact with the aluminum plate 12. The "nugget" is a portion where melting and solidification occur in the welded portion in the overlap resistance welding, but in the present specification, a melted portion where the nugget is formed at the time of solidification (i.e., a melted portion before solidification) may be referred to as a nugget.
In addition, in the plate group in which heat radiation to the electrode is not easily generated when the thickness of the steel plate is large, the energization suspension time tcPreferably 10ms or more, more preferably 20ms or more. And, the conduction stop time tcThe relationship of the following formula (9) is preferably satisfied, and the relationship of the following formula (10) is more preferably satisfied. This is because, by temporarily cooling the welded portion, heat generation in a wide range in the second energization step is promoted, and the joint strength is improved.
Figure BDA0002217812110000131
Figure BDA0002217812110000132
The welding current (current when energized) in the present invention is not particularly limited, and is, for example, 4 to 40 kA. However, since it is necessary to obtain a predetermined nugget diameter during the construction and an excessive current value causes the occurrence of spattering, the current I in the first energization step1For example, 4 to 20kA, the current value I of the second energization step2For example, 10 to 40 kA.
The pressing force during welding is not particularly limited, and may be, for example, 2.0kN to 7.0kN, or may be changed during welding and before and after welding.
Further, there is no problem in using a control method in which parameters such as a resistance value and a voltage value during welding are monitored and a current value and an energization time are changed in accordance with a change in the parameters.
In the present specification, the above formulae define only the relationship between numerical values.
Examples
The following illustrates embodiments of the present invention. It should be noted that the plate group, the welding conditions, and the electrode shape used in this example are examples of applications for showing the effects of the present invention, and it goes without saying that other conditions may be used.
(inventive examples and comparative examples)
As test materials, steel sheets 11 and aluminum sheets 12 shown in tables 1-1 and 1-2 were used. The tensile strength of each steel sheet shown in tables 1-1 and 1-2 was determined by preparing a tensile test piece No. JIS5 from the steel sheet in a direction parallel to the rolling direction and making the tensile test piece in accordance with JIS Z2241: 2011 was determined by performing a tensile test. Resistance spot welding was performed on the steel sheet 11 and the aluminum sheet 12 shown in table 1-1 as shown in fig. 2, and a resistance spot welded joint composed of a double-layered plate group was manufactured. Although not shown, resistance spot welding was similarly performed on the steel sheets and the aluminum sheets shown in tables 1 to 2 to manufacture a resistance spot welded joint composed of a three-layer plate group in which another steel sheet 15 (middle plate) was further interposed between a steel sheet 11 (lower plate) and an aluminum sheet 12 (upper plate). The aluminum plate 12 used has an oxide film formed on the surface thereof. The welding machine used an inverter dc resistance spot welding machine, and the radius of curvature and the tip diameter of the tips of the electrodes 13 and 14, and the energization pattern were set to the conditions shown in table 2. All of the electrodes 13 and 14 are DR electrodes made of chromium copper. The resistance spot welding is performed at room temperature (20 ℃), and is performed in a state in which the electrodes 13, 14 are constantly water-cooled. The pressurizing force is set to be constant in the first energization step, the energization suspension step, and the second energization step. In the first energization step, a part of the aluminum plate 12 is melted.
The obtained resistance spot welded joint was subjected to a cross tensile test according to JIS Z3137, and the peel strength was evaluated. The Cross Tensile Strength (CTS) was set to be A when CTS was 0.9kN or more, B when CTS was 0.9kN > CTS 0.8kN, C when CTS was 0.8kN > CTS 0.7kN, and F when CTS was 0.7kN > CTS, and the evaluation was performed. The evaluation results are shown in table 2. In the present invention example, one of A to C was evaluated.
Further, the first energization step was performed under the same conditions as described above, and the cross-sectional view of the joint was observed to determine the nugget diameter (mm) of the aluminum plate 12 formed during energization in the first energization step. The nugget diameter of the aluminum plate 12 was measured as the maximum diameter of the nugget of the aluminum plate 12 at the joint surface between the aluminum plate 12 and the plate in contact with the aluminum plate 12 (the steel plate 11, and the steel plate 15 in the case of the three-layer plate group shown in table 1-2). The measurement results are shown in table 2.
Figure BDA0002217812110000151
Figure BDA0002217812110000161
Figure BDA0002217812110000171
Description of the symbols
11. 15 steel plate
12 aluminum plate
13. 14 electrodes
21 welding current
22 near the contact end of the steel plate with the electrode

Claims (5)

1. A method for manufacturing a resistance spot weld joint by joining a plate group, which is formed by stacking at least one steel plate selected from a plated steel plate, a cold-rolled steel plate and a hot-rolled steel plate on an aluminum plate and by sandwiching one of the outermost plates as the steel plate and the other as the aluminum plate between a pair of electrodes, by resistance spot welding, the method comprising:
with a current I1kA at energization time t1A first energization step of energizing for an ms period;
after the first energization step, at an energization suspension time tcAn energization suspending step of suspending energization for an ms period; and
after the power-on stopping process, the current I is used2kA at energization time t2A second energization step of energizing for an ms period,
the total thickness of the laminated steel plates is set to TFemm, electrode to be in contact with steel plateThe radius of curvature of the tip is set to RFemm, and the diameter of the tip of the electrode in contact with the steel plate is DFeWhen the thickness is mm, the thickness is small,
the first energization step, the energization suspension step and the second energization step satisfy all of the relationships of the following expressions (1) to (6),
I1＜I2 (1)
t1＞t2 (2)
t1≥40 (3)
tc≥5 (4)
Figure FDA0002799600010000011
RFe≥20 (6)。
2. the method of manufacturing a resistance spot weld joint according to claim 1, wherein the first energization step, the energization suspension step, and the second energization step further satisfy the relationship of the following expression (7),
RFe≥50 (7)。
3. the method of manufacturing a resistance spot weld joint according to claim 1 or 2, wherein a radius of curvature of a tip of the electrode in contact with the aluminum plate is set to RAlmm, the first energization step, the energization suspension step and the second energization step further satisfy the relationship of the following expression (8),
RAl≥50 (8)。
4. the method of manufacturing a resistance spot weld joint according to claim 1 or 2, wherein at least a portion of the aluminum plate with which the electrode is in contact is melted in the first energization step.
5. The method of manufacturing a resistance spot weld joint according to claim 3, wherein at least a portion of the aluminum plate with which the electrode is in contact is melted in the first energization step.
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