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
• • 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
• • 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 mechanical strength and toughness Lithium copper aluminum alloy with improved mechanical 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.
• Products especially thick rolled products, forged or spun aluminum alloy are developed to produce by cutting, surfacing or mass machining of high strength parts intended especially for the aviation industry, the aerospace industry or mechanical construction.
• 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 to other properties of use must reach that of commonly used alloys, in particular in terms of a compromise between the static mechanical strength properties (yield strength, resistance to rupture) and the properties of damage tolerance (toughness, resistance to the propagation of fatigue cracks), these properties being in general antinomic.
• these properties must in particular be obtained at quarter and at mid-thickness and the products must therefore have a low sensitivity to quenching.
• a product is said to be quench sensitive if its static mechanical characteristics, such as its yield strength, decrease as quenching speed decreases.
• the quenching rate is the average cooling rate of the product during quenching.
• These alloys must also have sufficient corrosion resistance, be able to be shaped according to the usual methods and have low residual stresses so that they can be machined integrally.
• 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.
• US Pat. No. 5,234,662 describes alloys of composition (in% by weight), Cu: 2.60-3.30, Mn: 0.0-0.50, Li: 1.30-1.65, Mg: 0, 0 - 1.8, elements controlling the granular structure selected from Zr and Cr: 0.0 - 1.5.
• 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.
• the problem of aging products for civil aviation applications is not mentioned because the products concerned are essentially cryogenic tanks for rocket launchers or space shuttle.
• 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, Sc, V, especially having Kic toughness ( L)> 37.4 MPaVm for a yield strength R p o, 2 (L)> 448.2 MPa (thickness of products higher than 76.2 mm) and in particular a toughness K IC (L)> 38.5 MPaVm for a yield point Rp o, 2 (L)> 489.5 MPa (products with a thickness of less than 76.2 mm).
• 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.
• AA2050 alloy is also known which comprises (% by weight): (3.2-3.9) Cu, (0.7-1.3) Li, (0.20-0.6) Mg, (0 , 20-0.7) Ag, 0.25max. Zn, (0.20-0.50) Mn, (0.06-0.14) Zr and AA2095 (3.7-4.3) Cu, (0.7-1.5) Li, (0.25-0.8) Mg, (0.25-0.6) Ag, 0.25max. Zn, 0.25 max. Mn, (0.04-0.18) Zr.
• AA2050 alloy products are known for their quality in terms of static strength and toughness.
• a first object of the invention is a wrought product such as a product spun, rolled and / or forged, aluminum alloy comprising, in% by weight,
• a second subject of the invention is a process for manufacturing a spun, rolled and / or forged aluminum alloy product in which a) an aluminum-based liquid metal bath comprising 3 is produced, 0 to 3.9% by weight of Cu, 0.8 to 1.3% by weight of Li, 0.6 to 1.0% by weight of Mg, 0.05 to 0.18% by weight of Zr, 0.0 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, at most 0.15% by weight of Zn at least one element selected from Cr, Sc, Hf and Ti, the amount of said element, if selected, being 0.05 to 0.3 wt.% for Cr and for Sc, 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 aluminum residue; b) pouring a raw form from said bath of liquid metal; c) homogenizing said crude form at a temperature of between 450
• Yet another object of the invention is a structural element comprising a product according to the invention.
• Yet another object of the invention is the use of a structural element according to the invention for aeronautical construction.
• FIG. 2 Results of yield strength and toughness obtained for the samples of Example 1.
• FIG. 3 Results of yield strength and toughness obtained for the samples of Examples 1 and 2, the elastic limit being close to the peak.
• FIG. 4 Results of yield strength and toughness obtained for the samples of Example 3, the yield strength being close to the peak.
• 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 other words the tensile strength R m , the conventional yield stress at 0.2% elongation R p0 ⁇ ("yield strength") and elongation at break A%, are determined by a tensile test according to EN 10002-1, the sampling and the direction of the test being defined by the standard EN 485-1.
• KQ The stress intensity factor
• the thickness of the profiles is defined according to EN 2066: 2001: the cross section is divided into elementary rectangles of dimensions A and B; A being always the largest dimension of the elementary rectangle and B can be considered as the thickness of the elementary rectangle. The sole is the elementary rectangle with the largest dimension A.
• the ASTM Acetic Acid Sait Intermittent Spray (MASTMAASIS) test is performed according to ASTM G85.
• 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), wings (such as wing skin), stiffeners (stringers or stiffeners), ribs (ribs) and spars) and the empennage composed in particular of horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as the floor beams, the seat tracks and the doors.
• fuselage such as fuselage skin, fuselage skin in English
• stiffeners or stringers such as wing skin
• wings such as wing skin
• stiffeners stringers or stiffeners
• ribs ribs
• spars spars
• the empennage composed in particular of horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as the floor beams, the seat tracks and the doors.
• the present inventors have found that, surprisingly, it is possible to improve the compromise between the static mechanical strength properties and the damage tolerance properties, in particular of thick products made of aluminum-copper-lithium alloys, such as in particular the alloy. AA2050, by increasing the magnesium content.
• the choice of copper, magnesium and lithium contents makes it possible to reach a compromise of favorable properties and to obtain a satisfactory thermal stability of the product.
• the copper content of the products according to the invention is between 3.0 and 3.9% by weight. In an advantageous embodiment of the invention, the copper content is between 3.2 and 3.7% by weight.
• the toughness is not sufficient especially for income close to the peak and, moreover, the density of the alloy is not advantageous.
• the copper content is too low, the minimum static mechanical characteristics are not reached.
• the lithium content of the products according to the invention is between 0.8 and 1.3% by weight.
• the lithium content is between 0.9% and 1.2% by weight.
• the lithium content is at least 0.93% by weight or even at least 0.94% by weight.
• the magnesium content of the products according to the invention is between 0.6 and 1.0% by weight and preferably between 0.65 or 0.67 and 1.0% by weight.
• the magnesium content is at most 0.9% by weight and preferably at most 0.8% by weight. For some applications, it is advantageous that the magnesium content is at least 0.7% by weight.
• the zirconium content is between 0.05 and 0.18% by weight and preferably between 0.08 and 0.14% by weight so as to obtain preferably a fibered or slightly recrystallized grain structure.
• the manganese content is between 0.0 and 0.5% by weight. In particular for the manufacture of thick plates, a manganese content of between 0.2 and 0.4% by weight makes it possible to improve the toughness without compromising the mechanical strength.
• the silver content is between 0.0 and 0.5% by weight. The present inventors have found that, although the presence of silver is advantageous, in the presence of a quantity of magnesium according to the invention a significant amount of silver is not necessary to obtain the desired improvement in the compromise between mechanical resistance and damage tolerance. The limitation of the amount of money is economically very favorable.
• the silver content is between 0.15 and 0.35% by weight. In one embodiment of the invention, which has the advantage of minimizing the density, the silver content is at most 0.25% by weight.
• 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.
• a controlled and limited iron and silicon content contributes to the improvement of 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, Sc, Hf and Ti, the amount of the element, if selected, being from 0.05 to 0.3 % by weight for Cr and for Sc, 0.05 to 0.5% by weight for Hf and from 0.01 to 0.15% by weight for Ti.
• Preferably, between 0.02 and 0.10% by weight of titanium is chosen.
• Zinc is an undesirable impurity.
• the zinc content is Zn ⁇ 0.15% by weight and preferably Zn ⁇ 0.05% by weight. The zinc content is advantageously less than 0.04% by weight.
• the density of the products according to the invention is less than 2.72 g / cm 3 .
• the composition can advantageously be selected to obtain a density of less than 2.71 g / cm 3 and preferably less than 2.70 g / cm 3 .
• the alloy according to the invention is particularly intended for the manufacture of thick products, spun, rolled and / or forged. By thick products is meant in the context of the present invention, products whose thickness is at least 30 mm and preferably at least 50 mm. Indeed the alloy according to the invention has a low sensitivity to quenching which is particularly advantageous for thick products.
• the rolled products according to the invention preferably have a thickness of between 30 and 200 mm and preferably between 50 and 170 mm.
• the thick products according to the invention have a compromise between mechanical strength and particularly advantageous toughness.
• a product according to the invention in a rolled state, dissolved, quenched and tempered so as to reach a limit of elasticity close to the peak, having at least one of the following pairs of characteristics at thicknesses between thicknesses between 30 and 100 mm:
• thinner products are preferred, the thickness of which is between 10 and 30 mm, typically about 20 mm, because the compromise obtained under these conditions between strength and toughness is particularly advantageous.
• a product according to the invention in a rolled state, dissolved, quenched and tempered so as to reach a limit of elasticity close to the peak, having at least one of the following pairs of characteristics at thicknesses between thicknesses between 10 and 30 mm:
• the products according to the invention also have advantageous properties in terms of fatigue behavior both from the point of view of crack initiation (SfN) and propagation speed (da / dN).
• the corrosion resistance of the products of the invention is generally high; thus, the MASTMAASIS test result (ASTMG85 & G34 standards) is at least EA and preferably P for the products according to the invention.
• the method of manufacturing the products according to the invention comprises stages of preparation, casting, wrought, solution, quenching and tempering.
• 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 in a raw form, such as a billet, a rolling plate or a forging blank.
• the crude form is then homogenized at 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 raw form is generally cooled to room temperature before being preheated for hot deformation.
• Preheating aims to achieve a temperature preferably between 400 and 500 0 C and preferably of the order of 450 0 C allowing the deformation of the raw form.
• Hot deformation and optionally cold deformation is typically performed by spinning, rolling and / or forging to obtain a spun, rolled and / or forged product preferably having a thickness of at least 30 mm.
• the product thus obtained is then put in solution by heat treatment between 490 and 530 0 C for 15 min to 8 h, then quenched typically with water at room temperature or preferably cold water.
• the product then undergoes controlled traction with a permanent deformation of 1 to 6% and preferably of at least 2%.
• the rolled products preferably undergo controlled pulling with a permanent deformation greater than 3%.
• the controlled traction is carried out with a permanent deformation of between 3 and 5%.
• a preferred metallurgical state is the state
• 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% is carried out before achieving a controlled pull with a permanent deformation of 1 to 3%.
• An income is made comprising heating at a temperature between 130 and 170 0 C and preferably between 150 and 160 0 C for 5 to 100 hours and preferably from 10 to 40h so as to achieve a yield strength R p0> 2 close to the elastic limit R p0> 2 at the peak.
• R p0> 2 close to the elastic limit R p0> 2 at the peak.
• a point N of the yield curve, of duration equivalent to 155 0 C N and of elastic limit R p0 , 2 (N) is close to the peak by determining the slope P N the tangent to the income curve at the point N. It is considered in the context of the present invention that the elastic limit of a point N of the yield curve is close to the yield strength at the peak if the value absolute slope P N is at most 3 MPa / h. As illustrated by FIG. 1, an under-income state is a state for which P N is positive and an over-income state is a state for which P N is negative.
• the equivalent time t at 155 ° C. is defined by the formula: where T (in Kelvin) is the instantaneous metal processing temperature, which changes with time t (in hours), and T ref is a reference temperature set at 428Kt; is expressed in hours.
• T (in Kelvin) is the instantaneous metal processing temperature, which changes with time t (in hours)
• T ref is a reference temperature set at 428Kt; is expressed in hours.
• the elastic limit close to the yield strength at the peak is typically at least 90%, generally even at least 95% and frequently at least 97% of the elastic limit R p0,2 at the peak.
• the yield strength at the peak is generally satisfactorily evaluated by varying the residence time between 10 and 70 h for a temperature of 155 ° C. after a pull of 3.5%.
• the clearly underdeveloped states correspond to compromises between the static mechanical resistance (Rpo, 2, Rm) and the damage tolerance (toughness, resistance to crack propagation in fatigue) more interesting than peak and a fortiori that beyond the peak.
• the present inventors have found that a state under income but close to the peak makes it possible both to obtain a compromise between static mechanical resistance and damage tolerance of interest, but also to improve the performance in terms of corrosion resistance and thermal stability.
• the use of an under-income state close to the peak makes it possible to improve the robustness of the industrial process: a variation in the income conditions leads to a small variation in the properties obtained.
• the products according to the invention are particularly advantageous for producing products that are machined in the mass, such as, in particular, intrados or extrados elements whose skin and stiffeners come from the same starting material, longitudinal members and ribs, and than any other use where the present properties could be advantageous
• Table 1 Composition in% by weight and density of Al-Cu-Li alloys cast in the form of the EU. (Ref: reference; Inv: invention).
• Ti target 0.02% by weight for alloys 1 to 6
• the plates were homogenized at approximately 500 ° C. for approximately 12 hours and then debited and scalped to obtain slugs of size 400 ⁇ 335 ⁇ 90 mm.
• the slabs were hot rolled to obtain sheets having a thickness of 20 mm.
• the sheets were dissolved at 505 +/- 20 ° C. for 1 h, quenched with water at 75 ° C. so as to obtain a cooling rate of approximately 18 ° C./s and thus to simulate the properties obtained. at mid-thickness of sheet of thickness 80 mm.
• the sheets were then trimmed with a permanent elongation of 3.5%.
• the sheets received an income of between 10 h and 50 h at 155 ° C. Samples were taken at mid-thickness to measure the static mechanical characteristics in traction as well as the tenacity K Q.
• K Q obtained from this specimen type are lower than those obtained from samples having a thickness and a greater width.
• the products according to the invention have a significantly improved property compromise compared to the reference products.
• Table 3 Composition in% by weight and density of Al-Cu-Li alloys cast in plate form.
• the plates were homogenized and then scalped. After homogenization, the plates were hot-rolled to obtain sheets having a thickness of 50 mm. The sheets were dissolved in cold water and fractionated with a permanent elongation of between 3.5% and 4.5%
• points 8, 9 and 10 have been added to FIG. 2 (slope P N between 0 and 3), although they relate to specimens of different geometry for the measurement of K Q (K IC ) in order to facilitate the comparison between the invention and the prior art.
• K Q K IC
• the plates were homogenized at approximately 500 ° C. for approximately 12 hours and then debited and scalped to obtain slugs of size 400 ⁇ 335 ⁇ 90 mm.
• the slabs were hot rolled to obtain sheets having a thickness of 20 mm.
• the sheets were dissolved at 505 +/- 20 ° C. for 1 h and quenched with cold water. The sheets were then trimmed with a permanent elongation of 3.5%.
• the products according to the invention have a significantly improved property compromise compared to the reference samples.
• Alloy plates 12 transformed by the method described in Example 3 up to the excluded income stage were tempered at 155 ° C. or at 143 ° C. for increasing periods of time indicated in Table 7.
• the sheets having were returned 34h at 143 0 C and 40h at 155 0 C were then aged for 1000 hours at 85 0 C. Samples were taken at mid-thickness to measure the static mechanical characteristics in traction before and after aging.

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