Classifications

• • 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
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
• • 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
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
  • C22C21/16—Alloys based on aluminium with copper as the next major constituent with magnesium
• • 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
  • C22F1/057—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 copper as the next major constituent

Definitions

• Lithium copper aluminum alloy with improved compressive strength and toughness Lithium copper aluminum alloy with improved compressive strength and toughness
• the invention relates to aluminum-copper-lithium alloy products, more particularly, such products, their manufacturing and use processes, intended in particular for aeronautical and aerospace construction.
• Aluminum alloy rolled products are developed to produce high strength parts for the aerospace industry and the aerospace industry in particular.
• Aluminum alloys containing lithium are very interesting in this respect, since lithium can reduce the density of aluminum by 3% and increase the modulus of elasticity by 6% for each weight percent of lithium added.
• their performance compared with the other properties of use must reach that of the alloys commonly used, in particular in terms of a compromise between the static mechanical strength properties (yield strength in tension and in compression, breaking strength) and the properties of damage tolerance (toughness, fatigue crack propagation resistance), these properties being in general antinomic.
• the yield strength in compression is an essential property.
• These mechanical properties must also preferably be stable over time and have good thermal stability, that is to say, not be significantly modified by aging at a temperature of use.
• No. 5,032,359 discloses a broad family of aluminum-copper-lithium alloys in which the addition of magnesium and silver, in particular between 0.3 and 0.5 percent by weight, makes it possible to increase the mechanical strength.
• No. 5,455,003 discloses a process for manufacturing Al-Cu-Li alloys which have improved mechanical strength and toughness at cryogenic temperature, in particular through proper work-hardening and tempering.
• US Pat. No. 7,438,772 describes alloys comprising, in percentage by weight, Cu: 3-5, Mg: 0.5-2, Li: 0.01-0.9 and discourages the use of higher lithium content because of degradation of the compromise between toughness and mechanical strength.
• US Pat. No. 7,229,509 describes an alloy comprising (% by weight): (2.5-5.5) Cu, (0.1-2.5) Li, (0.2-1.0) Mg, (0, 2-0.8) Ag, (0.2-0.8) Mn, 0.4 max Zr or other grain refining agents such as Cr, Ti, Hf, Se, V.
• US patent application 2009/142222 A1 discloses alloys comprising (in% by weight), 3.4 to 4.2% Cu, 0.9 to 1.4% Li, 0.3 to 0.7% of Ag, 0.1 to 0.6% Mg, 0.2 to 0.8% Zn, 0.1 to 0.6% Mn and 0.01 to 0.6% of at least one element. for the control of the granular structure. This application also describes a process for manufacturing spun products.
• a first object of the invention is a process for manufacturing a laminated product based on aluminum alloy in which, successively,
• an aluminum-based liquid metal bath comprising 4.2 to 4.6 wt.% Cu, 0.8 to 1.30 wt.% Li, 0.3 to 0.8 wt. weight of Mg, 0.05 to 0.18% by weight of Zr, 0.05 to 0.5% by weight of Ag, 0.0 to 0.5% by weight of Mn, at most 0.20% by weight of Fe + Si, less than 0.20% by weight of Zn, at least one element selected from Cr, Se, Hf and Ti, the amount of said element, if chosen, being from 0.05 to 0 , 3% by weight for Cr and for Se, 0.05 to 0.5% by weight for Hf and from 0.01 to 0.15% by weight for Ti, the other elements at most 0.05% by weight each and 0.15% by weight in total, the balance aluminum;
• said laminating plate is hot-rolled into a sheet while maintaining the temperature above 400.degree. C. and preferably above 420.degree. C. e) said sheet is placed in solution at 490.degree. to 530.degree. h and quenching said product;
• said sheet is controlledly tensile with a permanent deformation of 2 to 3.5% and preferably of 2.0 to 3.0%,
• a second subject of the invention is a laminated product with a thickness of between 8 and 50 mm and a substantially non-recrystallized granular structure obtainable by the process according to the invention having at least one thickness at least one of the combinations. of following characteristics:
• Another object of the invention is an aircraft structure element, preferably an extrados wing skin, comprising a product according to the invention.
• Yet another object of the invention is the use of a product according to the invention or a structural element according to the invention for aeronautical construction.
• Figure 1 Example of income curve and determination of the slope of the tangent P.
• Figure 2 Evolution of the elastic limit in compression and the elastic limit in tension with the permanent deformation during the controlled traction.
• Figure 3 Compromise of property between the yield strength in compression and the toughness K app for the alloys No. 2 to No. 5 of Example 2.
• alloys are in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The density depends on the composition and is determined by calculation rather than by a method of measuring weight. The values are calculated in accordance with the procedure of The Aluminum Association, which is described on pages 2-12 and 2-13 of "Aluminum Standards and Data". The definitions of the metallurgical states are given in the European standard EN 515.
• the static mechanical characteristics in tension in other words the tensile strength R m , the conventional yield stress at 0.2% elongation R p0 , 2 , and the elongation at break A%, are determined by a tensile test according to standard NF EN ISO 6892-1, the sampling and the direction of the test being defined by the EN 485-1 standard.
• the yield strength in compression was measured at 0.2% compression according to ASTM E9.
• KQ The stress intensity factor
• a curve of the stress intensity as a function of the crack extension, known as the curve R, is determined according to ASTM E 561.
• the critical stress intensity factor Ko in other words the factor of intensity which makes the crack unstable, is calculated from the curve R.
• the stress intensity factor Kco is also calculated by assigning the initial crack length to the critical load at the beginning of the monotonic load. These two values are calculated for a specimen of the required form. K app represents the Kco factor corresponding to the specimen that was used to perform the R curve test.
• EN 12258 Unless otherwise specified, the definitions of EN 12258 apply.
• a "structural element” or “structural element” of a mechanical construction is called a mechanical part for which the static and / or dynamic mechanical properties are particularly important for the performance of the structure, and for which a structural calculation is usually prescribed or realized.
• These are typically elements whose failure is likely to endanger the safety of said construction, its users, its users or others.
• these structural elements include the elements that make up the fuselage (such as fuselage skin, fuselage skin in English), stiffeners or stringers, bulkheads, fuselage (circumferential frames), the wings (such as upper or lower wing skin, stringers or stiffeners), ribs and spars) and the composite empennage including horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as floor beams, seat tracks and doors.
• fuselage such as fuselage skin, fuselage skin in English
• stiffeners or stringers such as upper or lower wing skin, stringers or stiffeners
• ribs and spars such as upper or lower wing skin, stringers or stiffeners
• spars such as upper or lower wing skin, stringers or stiffeners
• composite empennage including horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as floor beams, seat tracks and doors.
• a selected class of aluminum alloys which contain specific and critical amounts of lithium, copper, magnesium, silver and zirconium makes it possible to prepare, under certain processing conditions, rolled products having a compromise improved between toughness, tensile yield strength and yield strength in compression.
• the present inventors have found that, surprisingly, it is possible to improve the compression elasticity limit for these alloys by choosing specific transformation process parameters, in particular during hot deformation and controlled tensile control. .
• the copper content of the products according to the invention is between 4.2 and 4.6% by weight. In an advantageous embodiment of the invention, the copper content is at least 4.3% by weight. A maximum copper content of 4.4% by weight is preferred.
• the lithium content of the products according to the invention is between 0.8% or 0.80% and 1.30% and preferably 1.15% by weight.
• the lithium content is at least 0.85% by weight.
• a maximum lithium content of 0.95% by weight is preferred.
• the increase in the copper content and to a lesser extent in the lithium content contributes to improving the static mechanical resistance, however, the copper having a detrimental effect especially on the density, it is preferable to limit the copper content to the maximum value preferred.
• the preferred lithium content of between 0.85% and 0.95% by weight in an embodiment makes it possible to improve the compromise between mechanical strength (yield strength in tension and in compression) and toughness and, moreover, the toughness attained for an income at or near the peak is higher.
• the preferred lithium content is between 1.10% and 1.20% by weight. weight, preferably associated with a magnesium content of between 0.50% or preferably 0.53% and 0.70% or preferably 0.65% by weight.
• the magnesium content of the products according to the invention is between 0.3% or 0.30% and 0.8 or 0.80% by weight.
• the magnesium content is at least 0.40% or even 0.45% by weight, which simultaneously improves static mechanical strength and toughness.
• the present inventors have found that the combination of a magnesium content of between 0.50% or preferably 0.53% and 0.70% or preferentially 0.65% by weight and a lithium content of between 0.85% and 1.15% by weight and preferably between 0.85% and 0.95% by weight leads to a compromise between mechanical strength (yield strength in tension and in compression) and particularly advantageous toughness, while keeping a rate of failure during the acceptable transformation, and therefore satisfactory reliability of the manufacturing process.
• the zirconium content is between 0.05 and 0.18% by weight and preferably between 0.08 and 0.14% by weight. In an advantageous embodiment of the invention, the zirconium content is at least 0.11% by weight.
• the manganese content is between 0.0 and 0.5% by weight. In one embodiment of the invention, the manganese content is between 0.2 and 0.4% by weight. In another embodiment of the invention, the manganese content is less than 0.1% by weight and preferably less than 0.05% by weight, which allows for the products obtained by the process according to the invention. to reduce the amount of insoluble metal phases and further improve the tolerance to damage.
• the silver content is between 0.05% and 0.5% by weight. In an advantageous embodiment of the invention, the silver content is between 0.10 and 0.40% by weight.
• the addition of silver contributes to improving the compromise of mechanical properties of the products obtained by the process according to the invention.
• the sum of the iron content and the silicon content is at most 0.20% by weight.
• the iron and silicon contents are each at most 0.08% by weight.
• the iron and silicon contents are at most 0.06% and 0.04% by weight, respectively. Controlled iron and silicon content and Limited contributes to improving the compromise between mechanical resistance and damage tolerance.
• the alloy also contains at least one element that can contribute to controlling the grain size selected from Cr, Se, Hf and Ti, the amount of the element, if selected, being from 0.05 to 0.3 % by weight for Cr and Se, 0.05 to 0.5% by weight for Hf and 0.01 to 0.15% by weight for Ti.
• Zinc is an undesirable impurity, especially because of its contribution to the density of the alloy.
• the zinc content is less than 0.20% by weight, preferably Zn ⁇ 0.15% by weight and most preferably Zn ⁇ 0.05% by weight.
• the zinc content is advantageously less than 0.04% by weight.
• the additive elements contributing to increase the density such as Cu, Zn, Mn and Ag are minimized and the elements contributing to decrease the density such as Li and Mg are maximized so as to reach a density lower than 2.73 g / cm 3 and preferably less than 2.70 g / cm.
• the manufacturing process of the products according to the invention comprises the steps of production, casting, homogenization, rolling with a temperature above 400 ° C, dissolution, quenching, traction between 2 and 3.5% and income.
• a bath of liquid metal is produced so as to obtain an aluminum alloy of composition according to the invention.
• the liquid metal bath is then cast as a rolling plate.
• the rolling plate is then homogenized so as to reach a temperature of between 450 ° C. and 550 ° C. and preferably between 480 ° C. and 530 ° C. for a period of between 5 and 60 hours.
• the homogenization treatment can be carried out in one or more stages.
• the rolling plate is generally cooled to room temperature before being preheated to be hot rolled.
• Preheating aims to achieve a temperature to maintain a temperature of at least 400 ° C and preferably at least 420 ° C during hot rolling.
• Intermediate reheating is achieved if during hot rolling the temperature decreases excessively.
• the hot rolling is carried out to a thickness of preferably between 8 and 50 mm and preferably between 12 and 40 mm.
• Significant cold deformation is typically a deformation of at least about 5% or 10%.
• the product thus obtained is then put in solution by heat treatment to reach a temperature between 490 and 530 ° C for 15 min to 8 h, and then typically quenched with water at room temperature or preferably cold water .
• essentially non-recrystallized By essentially non-recrystallized granular structure is meant a non-recrystallized granular structure content at mid-thickness greater than 70% and preferably greater than 85%.
• the product then undergoes controlled traction with a permanent deformation of 2 to 3.5% and preferably of 2.0% to 3.0%. Controlled traction with a maximum permanent deformation of about 2.5% is preferred.
• the present inventors have found that, surprisingly, the yield stress in compression decreases with increasing permanent deformations during controlled traction while the tensile yield strength increases under these conditions. There is therefore a permanent deformation by optimal controlled traction to obtain a yield strength in high compression while maintaining a limit of elasticity in sufficient traction.
• the permanent deformation by controlled traction is chosen so as to obtain a yield strength in compression at least equal to the yield strength limit.
• the present inventors have also found that surprisingly the effect of the permanent deformation rate on the compressive yield strength is specific to the rolled products, tests on the spun products have shown that such an effect is not observed in this case.
• Known steps such as rolling, planing, straightening shaping may optionally be performed after solution and quenching and before or after controlled pulling.
• a cold rolling step of at least 7% and preferably at least 9% and at most 15% is carried out after dissolution and quenching and before controlled pulling.
• An income is achieved in which the product reaches a temperature between 130 and 170 ° C and preferably between 150 and 160 ° C for 5 to 100 hours and preferably 10 to 70h.
• the income can be realized in one or more levels.
• the yield strength increases with the duration of tempering at a given temperature up to a maximum value called the peak of hardening or "peak” then decreases with the duration of income.
• the yield curve is defined as the evolution of the elastic limit as a function of the equivalent duration of income at 155 ° C.
• An example of an income curve is presented in FIG. 1.
• it is determined whether a point N of the income curve, of duration equivalent to 155 ° C. and elastic limit R p0 , 2 (N) is close to the peak by determining the slope P N of the tangent to the income curve at point N.
• an under-income state is a state for which P N is positive and an over-revenue state is a state for which PN is negative.
• the difference t N - t N- i is small, the variation of the elastic limit may be insignificant and the present inventors have found that a satisfactory approximation of P N is generally obtained when the difference t N - t N- i is between 2 and 20 hours and preferably is of the order of 3 hours.
• the equivalent time t at 155 ° C is defined by the formula:
• T in Kelvin
• T ref is a reference temperature set at 428Kt; is expressed in hours.
• the tensile or compressive yield strength can be used to determine if the income achieves a state close to the peak, however the results are not necessarily the same. In the context of the invention, it is preferred to use compression elastic limit values for the optimization of income.
• the clearly underdeveloped states correspond to compromises between the static mechanical resistance (Rp 0.2 , R m ) and the damage tolerance (toughness, resistance to propagation cracks in fatigue) more interesting than peak and a fortiori that beyond the peak.
• the present inventors have found that a state close to the peak makes it possible both to obtain a compromise between static mechanical resistance and damage tolerance that is of interest, but also to improve the performance in terms of corrosion resistance and thermal stability. .
• the rolled products obtained by the process according to the invention have, for a thickness of between 8 and 50 mm, at mid-thickness at least one of the following combinations of characteristics:
• Aircraft structural elements according to the invention comprise products according to the invention.
• a preferred aircraft structural element is an extrados wing skin.
• the use of a structural element incorporating at least one product according to the invention or manufactured from such a product is advantageous, in particular for aeronautical construction.
• the products according to the invention are particularly advantageous for producing extrados elements of aircraft wing.
• the plate was homogenized at about 500 ° C for about 20 hours.
• the plate was hot rolled at a temperature above 445 ° C to obtain 25 mm thick sheets.
• the sheets were dissolved at about 510 ° C for 5h, quenched with water at 20 ° C.
• the sheets were then tractionned with a permanent elongation of between 2% and 6%.
• the plates have experienced a single-stage income of 40 h at 155 ° C for 2% and 3% tractions, 30h for 4% and 20h for 6%, this income making it possible to achieve a yield strength in traction and in compression at the peak or near the peak.
• Samples were taken at mid-thickness to measure static mechanical tensile and compressive properties as well as KQ toughness.
• the structure of the sheets obtained was essentially non-recrystallized.
• the uncrystallized granular structure level at mid-thickness was 90%. Table 2. Mechanical properties obtained for the different sheets.
• Figure 2 shows the evolution of the elastic limit in tension and in compression as a function of the permanent elongation during controlled traction. For a permanent elongation during traction between 2 and 3.5% a favorable compromise is obtained between the yield strength in compression and the tensile yield strength. Thus, under these conditions, the yield strength in compression is greater than the tensile yield strength, the tensile elasticity remaining greater than 620 MPa.
• Example 2
• the plates were homogenized by a two-step treatment of 8 hours at 500 ° C. followed by 12 hours at 510 ° C. and then scalped. After homogenization, the plates were hot rolled to obtain sheets having a thickness of 9.4 mm with intermediate reheating in the case where the temperature decreases to minus 400 ° C. The sheets were dissolved for 5 h at approximately 510 ° C., quenched with cold water and triturated with a permanent elongation of 3%.
• the structure of the sheets obtained was essentially non-recrystallized.
• the uncrystallized granular structure level at mid-thickness was 90%.
• the sheets were tempered between 15 h and 50 h at 155 ° C. Samples were taken at mid-thickness to measure the static mechanical characteristics in tension, in compression as well as KQ toughness.
• Tenacity measurements were also obtained on CCT samples 300 mm wide and 6.35 mm thick. The results obtained are shown in Table 4.
• Figure 3 illustrates the compromise obtained between the yield strength in compression and the toughness K aD n.
• the combination of the preferred composition (Alloy No. 3) with the process according to the invention leads, in particular for a 50 hours income at 155 ° C., which is the most favorable from the point of view of thermal stability. a particularly favorable compromise between yield strength in compression, tensile yield strength and toughness.
• Example 3
• the plate was homogenized at about 500 ° C for about 30 hours.
• the plate was hot rolled at a temperature above 400 ° C to obtain 25 mm thick sheets.
• the sheets were dissolved at about 510 ° C for 5h, quenched with water at 20 ° C.
• the sheets were then tractionned with a permanent elongation of 2% or 3%.
• the structure of the sheets obtained was essentially non-recrystallized.
• the uncrystallized granular structure level at mid-thickness was greater than 90%.

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