EP3610047B1 - Aluminium-copper-lithium alloy products - Google Patents

Description

Field of the invention

The invention relates in general to wrought products in aluminium-copper-lithium alloys, and more particularly to such products in the form of sections intended to produce stiffeners in aeronautical construction.

State of the art

A continuous research effort is carried out in order to develop materials which can simultaneously reduce the weight and increase the efficiency of the structures of high performance aircraft. Aluminum alloys containing lithium are very attractive in this regard, as lithium can reduce the density of aluminum by 3% and increase the modulus of elasticity by 6% for each weight percent of lithium added. For these alloys to be selected in aircraft, their performance must match that of commonly used alloys, particularly in terms of the trade-off between static strength properties (yield strength, fracture toughness) and damage tolerance properties ( toughness, resistance to the propagation of fatigue cracks), these properties generally being contradictory. 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.

Several Al-Cu-Li alloys are known for which silver is added.

The patent US 5,032,359 describes a vast 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. These alloys are often known by the trade name “Weldalite ^™ ”.

The patent US 5,198,045 describes a family of Weldalite ^™ alloys comprising (wt%) (2.4-3.5)Cu, (1.35-1.8)Li, (0.25-0.65)Mg, (0 ,25-0.65)Ag, (0.08-0.25)Zr. THE Wrought products made with these alloys combine a density of less than 2.64 g/cm ³ and an interesting compromise between mechanical strength and toughness.

The patent US 7,229,509 describes a family of Weldalite ^™ alloys comprising (wt%) (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, (up to 0.4) Zr or other elements such as Cr, Ti, Hf, Sc and V. The examples shown have a compromise between mechanical strength and improved toughness but their density is greater than 2.7 g/cm ³ .

The patent application WO2007/080267 discloses a zirconium-free Weldalite ^™ alloy for use in fuselage sheets comprising (wt%) (2.1-2.8)Cu, (1.1-1.7)Li, (0.2- 0.6) Mg, (0.1-0.8) Ag, (0.2-0.6) Mn.

The AA2196 alloy is also known, comprising (in % by weight) (2.5-3.3) Cu, (1.4-2.1) Li, (0.25-0.8) Mg, (0 .25-0.6) Ag, (0.04-0.18) Zr and at most 0.35 Mn.

Limiting the amount of money is economically very favorable. However, it is noted that the products according to the prior art made of an alloy containing essentially no silver do not make it possible to obtain properties as advantageous as those of the products made with alloys containing silver such as the alloy AA2196.

There is a need for aluminum-copper-lithium alloy products, in particular extruded products, having a reduced density and properties substantially equivalent to those of known products containing silver, in particular in terms of compromise between the properties of static mechanical strength and damage tolerance properties. The thermal stability, the resistance to corrosion, the machinability and the density of these products in particular must also be satisfactory with respect to those of known products containing silver while having a low density.

Object of the invention

• Cu : 2,5-3,4 ; préférentiellement 2,8-3,2 ;
• Li : 1,6-2,2 ; préférentiellement 1,65-1,8 ;
• Mg : 0,4-0,9 ; préférentiellement 0,5-0,8 ;
• Mn : 0,2 - 0,6 ; préférentiellement 0,3-0,6 ;
• Zr : 0,08 - 0,18 ; préférentiellement 0,12-0,16 ;
• Zn : < 0,4 préférentiellement 0,05-0,4 ; plus préférentiellement de 0,2-0,4 ;
• Ag : < 0,15 ; préférentiellement <0,1 ; plus préférentiellement encore <0,05 ;
• Fe + Si ≤ 0,20 ;
• au moins un élément choisi parmi
  • Ti : 0,01 - 0,15 ; préférentiellement 0,01-0,05 ;
  • Sc : 0,01 - 0,15, préférentiellement 0,02-0,1 ;
  • Cr : 0,01 - 0,3, préférentiellement 0,02-0,1 ;
  • Hf : 0,01 - 0,5 ; préférentiellement 0,02-0,1 ;
  • V : 0,01 - 0,3, préférentiellement 0,01-0,05 ;
• autres éléments ≤ 0,05 chacun et ≤ 0,15 au total, reste aluminium.

A first object of the invention is an aluminum-based alloy product comprising, in% by weight,

• Cu: 2.5-3.4; preferentially 2.8-3.2;
• Li: 1.6-2.2; preferably 1.65-1.8;
• Mg: 0.4-0.9; preferably 0.5-0.8;
• Mn: 0.2 - 0.6; preferably 0.3-0.6;
• Zr: 0.08-0.18; preferably 0.12-0.16;
• Zn: <0.4 preferably 0.05-0.4; more preferably 0.2-0.4;
• Ag: <0.15; preferably <0.1; more preferably still <0.05;
• Fe + Si ≤ 0.20;
• at least one element chosen from
  • Ti: 0.01-0.15; preferably 0.01-0.05;
  • Sc: 0.01-0.15, preferably 0.02-0.1;
  • Cr: 0.01-0.3, preferably 0.02-0.1;
  • Hf: 0.01 - 0.5; preferably 0.02-0.1;
  • V: 0.01-0.3, preferably 0.01-0.05;
• other elements ≤ 0.05 each and ≤ 0.15 in total, rest aluminium.

1. a) élaboration d'un bain de métal liquide comprenant, en pourcentage en poids, Cu :
   • 2,5-3,4 ; Li : 1,6-2,2 ; Mg : 0,4-0,9 ; Mn : 0,2 - 0,6 ; Zr : 0,08 - 0,18 ; Zn : < 0,4 ;
   • Ag : < 0,15 ; Fe + Si ≤ 0,20 ; au moins un élément choisi parmi Ti, Sc, Cr, Hf et V, la teneur dudit élément, s'il est choisi, étant Ti : 0,01 - 0,15 ; Sc : 0,01 - 0,15 ; Cr :
   • 0,01 - 0,3 ; Hf : 0,01 - 0,5 ; V : 0,01 - 0,3 ; autres éléments ≤ 0,05 chacun et ≤ 0,15 au total, reste aluminium
2. b) coulée d'une forme brute à partir dudit bain de métal liquide ;
3. c) homogénéisation ladite forme brute ;
4. d) déformation à chaud et, optionnellement, à froid de la forme brute en un produit filé, laminé et/ou forgé ;
5. e) mise en solution et trempe dudit produit ;
6. f) traction de façon contrôlée dudit produit avec une déformation permanente de 1 à 15%, préférentiellement de 2 à 4% ;
7. g) revenu dudit produit par chauffage à 140 à 170°C pendant 5 à 70 heures. Avantageusement, le revenu est réalisé de façon à ce que ledit produit ait une limite d'élasticité conventionnelle mesurée à 0,2% d'allongement dans le sens L, R_p0,2 (L), d'au moins 510 MPa et une ténacité K_Q (L-T), dans le sens L-T, d'au moins 21 $\mathrm{MPa}\sqrt{\mathrm{m}}$
   
   et telle que K_Q(L-T) > -0,2667^∗R_p0,2(L) + 169.

A second object of the invention is a process for manufacturing an extruded, rolled and/or forged product based on an aluminum alloy, comprising the steps:

1. a) preparation of a bath of liquid metal comprising, in percentage by weight, Cu:
   • 2.5-3.4; Li: 1.6-2.2; Mg: 0.4-0.9; Mn: 0.2 - 0.6; Zr: 0.08-0.18; Zn: <0.4;
   • Ag: <0.15; Fe + Si ≤ 0.20; at least one element selected from Ti, Sc, Cr, Hf and V, the content of said element, if selected, being Ti: 0.01-0.15; sc: 0.01-0.15; Cr:
   • 0.01 - 0.3; Hf: 0.01 - 0.5; V: 0.01 - 0.3; other elements ≤ 0.05 each and ≤ 0.15 in total, remainder aluminum
2. b) casting a blank form from said bath of liquid metal;
3. c) homogenizing said raw form;
4. d) hot and, optionally, cold working of the raw shape into an extruded, rolled and/or forged product;
5. e) dissolving and quenching said product;
6. f) traction in a controlled manner of said product with a permanent deformation of 1 to 15%, preferably of 2 to 4%;
7. g) tempering said product by heating at 140 to 170°C for 5 to 70 hours. Advantageously, tempering is carried out so that said product has a conventional elastic limit measured at 0.2% elongation in the direction L, R _p0.2 (L), of at least 510 MPa and a toughness K _Q (LT), in the LT direction, of at least 21 $\mathrm{MPa}\sqrt{\mathrm{m}}$
   
   and such that K _Q (LT) > -0.2667 ^∗ R _p0.2 (L) + 169.

Yet another object of the invention is a structural element incorporating at least one product according to the invention.

Description of figures

• Figure 1 : Shape of the profile W of the example (the term "shape" is the cross section of said profile). Dimensions are given in mm. The samples used for the mechanical characterizations were taken from the area indicated by the dotted lines.
• Figure 2 : Shape of the profile Z of the example (the term "shape" means the cross section of said profile). Dimensions are given in mm. The samples used for the mechanical characterizations were taken from the area indicated by the dotted lines.
• Figure 3 : Compromise between toughness and mechanical resistance obtained for the profiles of the example.

Description of the invention

Unless otherwise stated, all indications regarding the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy. The designation of the alloys is made 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. Values are calculated in accordance with The Aluminum Association procedure, which is described pages 2-12 and 2.13 of “Aluminum Standards and Data”. The definitions of metallurgical tempers are given in the European standard EN 515 (2009).

Unless otherwise stated, the static mechanical characteristics, in other words the breaking strength R _m , the conventional yield strength at 0.2% elongation R _p0.2 ("yield strength") and l elongation at break A, are determined by a tensile test according to standard EN 10002-1 (2001), the sampling and direction of the test being defined by standard EN 485-1 (2016).

The stress intensity factor (K _Q ) is determined according to ASTM E 399 (2012). Thus, the proportion of specimens defined in paragraph 7.2.1 of this standard is always verified as well as the general procedure defined in paragraph 8. Standard ASTM E 399 (2012) gives in paragraphs 9.1.3 and 9.1.4 criteria which make it possible to determine whether K _Q is a valid value of K _1C . Thus, a K _1C value is always a K _Q value, the reciprocal not being true. In the context of the invention, the criteria of paragraphs 9.1.3 and 9.1.4 of standard ASTM E399 (2012) are not always verified, however for a given specimen geometry, the values of K _Q presented are always comparable to each other, the geometry of the specimen making it possible to obtain a valid value of K _1C not always being accessible given the constraints linked to the dimensions of the sheets or sections.

Unless otherwise stated, the definitions of EN 12258 (2012) apply. The thickness of the sections is defined according to standard EN 2066:2001: the cross section is divided into elementary rectangles of dimensions A and B; A always being the largest dimension of the elementary rectangle and B being able to be considered as the thickness of the elementary rectangle.

The term "structural element" or "structural element" of a mechanical construction is used here to mean 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 performed. These are typically elements whose failure is likely to endanger the safety of the said construction, of the users, of the users or of others. For an airplane, these elements of structure include in particular the elements that make up the fuselage (such as the fuselage skin), the fuselage stiffeners or stringers, the bulkheads (bulkheads), the fuselage frames (circumferential frames), the wings (such as the wing skin), the stiffeners (stringers or stiffeners), the ribs (ribs) and spars (spars) and the empennage composed in particular of horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as floor beams, seat tracks and doors.

According to the invention, a selected class of aluminum alloys containing specific and critical contents of copper, lithium, magnesium, zinc, manganese and zirconium but containing essentially no silver makes it possible to prepare products wrought having in particular an improved compromise between toughness and mechanical strength compared to that of products containing essentially no silver.

The present inventors have found that, surprisingly, it is possible for products to obtain a compromise that is at least equivalent between the properties of static mechanical strength and the properties of tolerance to damage than that obtained with an aluminum-copper-lithium alloy containing silver, such as in particular the AA2196 alloy, by making a narrow selection of the quantities of lithium, copper, magnesium, manganese, zinc and zirconium.

The copper content of the products according to the invention is between 2.5 and 3.4% by weight. In an advantageous embodiment of the invention, the copper content is at least 2.8 or preferably at least 2.9% by weight and/or at most 3.2 and preferably at most 3.1% by weight. weight.

The lithium content of the products according to the invention is between 1.6 and 2.2% by weight. Advantageously, the lithium content is between 1.65% and 1.8% by weight. Preferably, the lithium content is at most 1.75% by weight.

The magnesium content of the products according to the invention is between 0.4 and 0.9% by weight and preferably it is at least 0.5% by weight and, more preferably still greater than 0.6% in weight. Advantageously, the magnesium content is at plus 0.8% by weight. The present inventors have found that when the magnesium content is less than 0.30% by weight the advantageous compromise between mechanical strength and damage tolerance is not obtained.

The manganese content of the products according to the invention is between 0.2 and 0.6% by weight and, preferably, it is at least 0.3% by weight and, even more preferably at least 0.33% by weight and more preferably at least 0.4% by weight. In another embodiment, the manganese content is between 0.2 and 0.4% by weight, preferably between 0.25 and 0.35% by weight. The present inventors have found that when the manganese content is less than 0.2% by weight, the tenacity KQ (L-T), in the L-T direction, advantageous according to the invention is not obtained.

The zirconium content of the products according to the invention is between 0.08 and 0.18% by weight and, preferably, it is from 0.12 to 0.16% by weight and, even more preferably, 0 .14 to 0.15% by weight. In another embodiment, the zirconium content is advantageously between 0.09 and 0.12% by weight, preferably between 0.09 and 0.11% by weight, or even between 0.09 and 0.10% in weight.

The zinc content is less than 0.4% by weight, preferably it is 0.05 and 0.35% by weight. Advantageously, the zinc content is 0.2 to 0.3% by weight, which can contribute to achieving the desired compromise between toughness and mechanical strength.

The silver content is less than 0.15% by weight, preferably less than 0.10% by weight and, more preferably still, less than 0.05% by weight. The present inventors have found that the advantageous compromise between strength and damage tolerance known for alloys typically containing 0.2 to 0.4% by weight silver can be obtained for alloys containing essentially no silver. with the composition selection made.

The sum of the iron content and the silicon content is at most 0.20% by weight. Preferably, the iron and silicon contents are each at most 0.08% by weight. In an advantageous embodiment of the invention, the iron and silicon contents are at most 0.06% and 0.04% by weight, respectively.

The alloy also contains at least one element which can contribute to the control of the grain size chosen from among Ti, Sc, Cr, Hf and V, the content of the element, if chosen, being from 0.01 to 0 .15% by weight, preferably 0.01 to 0.05% by weight for Ti; from 0.01 to 0.15% by weight, preferably 0.02 to 0.1% by weight for Sc; 0.01 to 0.5% by weight, preferably 0.02 to 0.1% by weight for Hf and 0.01 to 0.3% by weight, preferably 0.02 to 0.1% by weight for Cr and from 0.01 to 0.3% by weight, preferably 0.01 to 0.05% by weight for V. Preferably, between 0.02 and 0.04% by weight of titanium is chosen.

The alloy according to the invention is particularly intended for the manufacture of rolled, extruded and/or forged products and, even more particularly, extruded products. The products according to the invention have a particularly advantageous compromise between mechanical strength and toughness.

The products according to the invention have, in a spun, solution-treated, tempered, drawn and tempered state, in particular for thicknesses up to 50 mm or even between 8 and 50 mm, or even between 15 and 35 mm, a yield strength measured at 0.2% elongation in the L direction, Rp0.2 (L), of at least 510 MPa and a toughness KQ (LT), in the LT direction, of at least 21 MPa√m and such that KQ (LT) > - 0.2667*Rp0.2 (L) + 169. According to a particularly advantageous embodiment, they have, under the conditions described above, a conventional yield strength measured at 0.2% elongation in the L direction, Rp0.2 (L), of at least 525 MPa and a toughness KQ (LT), in the LT direction, of at least 23 MPa√m and such that KQ (LT) > - 0.2667*Rp0.2 (L) + 171. In the present invention, the specimens used for the KQ measurements are of the CT type with a thickness of 20 mm and a width of 50 mm.

The process for manufacturing the products according to the invention comprises steps of production, casting, rolling, extrusion and/or forging, solution treatment, quenching, stress relieving and tempering.

In a first step, a bath of liquid metal is prepared so as to obtain an aluminum alloy of composition according to the invention.

The liquid metal bath is then cast in a raw form, typically a rolling plate, an extrusion billet or a forging blank.

The raw form is then homogenized at a temperature of between 450° C. and 550° and preferably between 520° C. and 530° C. for a period of between 6 and 15 hours.

After homogenization, the raw form is optionally cooled down to room temperature before being preheated with a view to being hot deformed. The hot deformation is carried out by rolling, extrusion and/or forging so as to obtain a rolled, extruded and/or forged product, preferably an extruded product.

The product thus obtained is then placed in solution by heat treatment between 490 and 550° C. for 15 min to 8 h, then quenched typically with water at room temperature.

The product then undergoes controlled stress relief, preferably by traction, with a permanent deformation of 1 to 15% and preferably of 2 to 4%. Advantageously, the extruded product has, at the end of the process steps detailed above, a thickness ranging up to 50 mm or even between 8 and 50 mm, or even between 15 and 35 mm.

et telle que K_Q (L-T) > -0,2667^∗R_p0,2 (L) + 169. Les présents inventeurs ont constaté que le compromis entre résistance mécanique et ténacité peut être amélioré en réalisant le revenu à une température comprise entre 150 à 165 °C pendant un temps à équivalent t _i à 160°C compris entre 15 et 28h, préférentiellement entre 20 et 27h, t _i étant défini par la formule : $${\mathrm{t}}_i=\frac{{\displaystyle \int \exp \left(-16400/\mathrm{T}\right)\mathrm{dt}}}{\exp \left(-16400/{\mathrm{T}}_{\mathrm{ref}}\right)}$$

où T (en Kelvin) est la température instantanée de traitement du métal, qui évolue avec le temps t (en heures), et T_ref est une température de référence fixée à 433 K.Tempering is carried out comprising heating at a temperature of between 140 and 170°C for 5 to 70 hours so that said product has a conventional yield strength measured at 0.2% elongation in the L direction, R _p0.2 (L), of at least 510 MPa and a toughness K _Q (LT), in the LT direction, of at least 21 $\mathrm{MPa}\sqrt{\mathrm{m}}$

and such that K _Q (LT) > -0.2667 ^∗ R _p0.2 (L) + 169. The present inventors have found that the compromise between mechanical strength and toughness can be improved by performing tempering at a temperature between 150 at 165°C for an equivalent time t _i at 160°C of between 15 and 28 hours, preferably between 20 and 27 hours, t _i being defined by the formula: $${\mathrm{you}}_I=\frac{{\displaystyle \int \exp \left(-16400/\mathrm{T}\right)\mathrm{dt}}}{\exp \left(-16400/{\mathrm{T}}_{\mathrm{ref}}\right)}$$

where T (in Kelvin) is the instantaneous metal treatment temperature, which changes over time t (in hours), and T _ref is a reference temperature fixed at 433 K.

According to a particularly advantageous embodiment, the extruded product with a conventional yield strength measured at 0.2% elongation in the L direction, Rp0.2 (L), of at least 525 MPa and a tenacity KQ ( L-T), in the L-T direction, of at least 23 MPa√m and such that KQ (L-T) > -0.2667*Rp0.2 (L) + 171. In said embodiment, the spun product advantageously has a thickness, up to 50 mm or between 8 and 50 mm, or even between 15 and 35 mm.

The products according to the invention can advantageously be used in structural elements, in particular aircraft. Thus, an object of the invention is a structural element incorporating at least one product according to the invention or a product manufactured using a process according to the invention.

The use of a structural element incorporating at least one product according to the invention or made from such a product is advantageous, in particular for aeronautical construction. The products according to the invention are particularly advantageous for the production of structural elements such as stiffeners or frames for the manufacture of intrados or extrados elements of an aircraft wing, preferably stiffeners, spars and ribs, or also floor beams and seat rails.

These and other aspects of the invention are explained in more detail using the following illustrative and non-limiting examples.

Example

In this example, several billets (384 mm in diameter) of Al-Cu-Li alloy whose composition is given in Table 1 were cast (alloys 67, 74 a and b, 66, 68 and 69). The composition of two alloys of the prior art AA2196 have also been given in table 1 below. Table 1. Composition in % by weight and density of the Al-Cu-Li alloys used Alloy Cu Li mg Zn Ag min Zr You 67 3.02 1.68 0.60 0.25 0.04 0.33 0.14 0.04 74a 2.98 1.67 0.56 0.05 0.03 0.32 0.15 0.04 74b 2.98 1.67 0.70 0.05 0.03 0.32 0.15 0.04 66 3.00 1.69 0.60 0.47 0.04 0.32 0.13 0.04 68 3.00 1.67 0.35 0.52 0.02 0.06 0.14 0.04 69 3.00 1.66 0.33 0.52 0.05 0.31 0.144 0.04 2 (Prior Art) 2.83 1.59 0.36 0.02 0.38 0.33 0.11 0.02 5 (Prior Art) 2.90 1.67 0.40 0.01 0.38 0.31 0.1 0.03 For all alloys 67, 74a and b, 66, 68 and 69, Fe and Si < 0.20% by weight and other elements less than 0.05% by weight each, 0.15% by total weight.

The alloy billets 67, 74 a and b, 66, 68 and 69 were then homogenized for 8 to 10 hours at 524°C. The billet in alloy 2 was homogenized for 8 hours at 500°C then 24 hours at 527°C while that in alloy 5 was homogenized for 8 hours at 520°C.

After homogenization, the billets were reheated to 450°C +/- 40°C then hot-spinned to obtain W profiles according to the figure 1 for alloy 2, 67, 74 a and b, 66, 68 and 69 and Z according to picture 2 for alloys 5. The profiles thus obtained were put in solution at 524°C, quenched and stretched with a permanent elongation of between 2 and 5%.

The profiles were subjected to tempering as indicated in Table 2: 30h at 152°C, 48h at 152°C, 30h at 160°C. For alloys 2 and 5, tempering was carried out for 48 hours at 152 °C. The equivalent times t _i at 160° C. were calculated taking into account the rise time to the tempering plateau and considering a rise rate of 20° C./h.

Samples taken from the end of the section were tested to determine their static mechanical properties as well as their toughness (K _Q ). The location of the samples is indicated in dotted lines on the figure 1 And 2 . The test pieces used for measuring the static properties were 10 mm in diameter and taken so that the direction of the axis of the test piece corresponded to the direction of spinning (direction L). The specimens used for the tenacity measurements were of the CT type and had the characteristics B=20 mm and W = 50 mm and were machined in such a way that the direction of loading corresponds to the direction of spinning and the direction of propagation is perpendicular. to the spinning direction and contained in the plane of the figure 1 And 2 (LT configuration).

The results obtained are given in table 2 below and illustrated by the picture 3 for the alloys in table 1. Table 2. Tempering conditions and Rp0.2 (L) and Kq (LT) properties of alloys Income teq 160°C (h) Rp0.2 (L) (MPa) Kq (LT) (MPa√m) 66 30h - 152°C 16.8 506 27.3 48h - 152°C 26.7 541 18.8 30h - 160°C 30.6 545 16.6 67 30h - 152°C 16.8 517 37.8 48h - 152°C 26.7 564 24.8 30h - 160°C 30.6 569 20.2 30h -155°C 21 545 33.1 40h - 152°C 22.2 548 29.0 9 p.m. - 160°C 21.6 542 27.7 68 30h - 152°C 16.8 524 17.3 48h - 152°C 26.7 548 15.1 30h - 160°C 30.6 545 14.9 69 30h - 152°C 16.8 551 20.9 48h - 152°C 26.7 566 16.6 30h - 160°C 30.6 560 15.7 74a 30h - 152°C 16.8 518 32.4 48h - 152°C 26.7 552 22.0 30h - 160°C 30.6 552 18.4 74b 30h - 152°C 16.8 515 38.7 48h - 152°C 26.7 550 23.0 30h - 160°C 30.6 557 18.5 2 48h - 152°C 26.7 522 37.6 5 48h - 152°C 26.7 536 38.2

Claims (11)

1. An aluminium alloy product comprising, in % by weight,

   Cu: 2.5-3.4; preferably 2.8-3.2;

   Li: 1.6-2.2; preferably 1.65-1.8;

   Mg: 0.4-0.9; preferably 0.5-0.8;

   Mn: 0.2-0.6; preferably 0.3-0.6;

   Zr: 0.08-0.18; preferably 0.12-0.16;

   Zn: <0.4, preferably 0.05-0.4; more preferably 0.2-0.4;

   Ag: <0.15; preferably <0.1; yet more preferably <0.05;

   Fe + Si ≤ 0.20;

   at least one element selected from Ti, Sc, Cr, Hf and V, the content of the element, if it is selected, being:

   Ti: 0.01 - 0.15; preferably 0.01-0.05;

   Sc: 0.01-0.15, preferably 0.02-0.1;

   Cr: 0.01 - 0.3, preferably 0.02-0.1;

   Hf: 0.01-0.5; preferably 0.02-0.1;

   V: 0.01-0.3, preferably 0.01-0.05;

   other elements ≤ 0.05 each and ≤ 0.15 in total, the rest being aluminium.
2. The product according to claim 1 wherein the copper content is 2.9 to 3.1% by weight.
3. The product according to any one of claims 1 to 2 wherein the lithium content is 1.65 to 1.75% by weight.
4. The product according to any one of claims 1 to 3 wherein the manganese content is 0.4 to 0.6% by weight.
5. The product according to any one of claims 1 to 3 wherein the zirconium content is 0.14 to 0.15% by weight.
6. A method for manufacturing an extruded, rolled and/or forged aluminium alloy product comprising the steps:

   a) preparing a liquid metal bath comprising, as a percentage by weight, Cu: 2.5-3.4; Li: 1.6-2.2; Mg: 0.4-0.9; Mn: 0.2-0.6; Zr: 0.08-0.18; Zn: <0.4; Ag: <0.15; Fe + Si ≤ 0.20; at least one element selected from Ti, Sc, Cr, Hf and V, the content of said element, if selected, being Ti: 0.01 - 0.15; Sc: 0.01 - 0.15; Cr: 0.01 - 0.3; Hf: 0.01-0.5; V: 0.01 - 0.3; other elements ≤ 0.05 each and ≤ 0.15 in total, the rest being aluminium

   b) casting an unwrought form from said liquid metal bath;

   c) homogenising said unwrought form;

   d) hot and, optionally, cold-working the unwrought form into an extruded, rolled and/or forged product;

   e) solution heat treating and quenching said product;

   f) stretching said product in a controlled manner with a permanent set of 1 to 15%, preferably of 2 to 4%;

   g) ageing said product by heating at 140 to 170°C for 5 to 70 hours so that said product has a conventional yield strength measured at 0.2% elongation in the L direction, R_p0.2 (L), of at least 510 MPa and a toughness K_Q (L-T), in the L-T direction, of at least 21 MPaVm and such that K_Q (L-T) > -0.2667^∗R_p0.2 (L) + 169.
7. The method according to claim 6 wherein the homogenisation temperature is comprised between 520 °C and 530°C and the treatment duration is comprised between 6 and 15 hours.
8. The method according to any one of claims 6 to 7 wherein the ageing is carried out at a temperature comprised between 150 to 165 °C for an equivalent time t _i at 160°C comprised between 15 and 28h, preferably between 20 and 27h, t _i being defined by the formula: $${\mathrm{t}}_i=\frac{{\displaystyle \int \exp \left(-16400/\mathrm{T}\right)\mathrm{dt}}}{\exp \left(-16400/{\mathrm{T}}_{\mathrm{ref}}\right)}$$

   

   where T (in Kelvin) is the instantaneous metal treatment temperature, which changes over time t (in hours), and T_ref is a reference temperature fixed at 433 K.
9. The product obtained according to any one of claims 6 to 8 characterised in that it has a conventional yield strength measured at 0.2% elongation in the L direction, R_p0.2 (L), of at least 525 MPa and a toughness KQ (L-T), in the L-T direction, of at least 23 MPaVm and such that KQ (L-T) > -0.2667*Rp0.2 (L) + 171.
10. A structural element incorporating at least one product according to any one of claims 1 to 5 or manufactured from a product obtained according to any one of claims 6 to 8.
11. Use of a structural element according to claim 10 as a stiffener or a frame of lower surface or upper surface of airplane wing elements, or a floor beam or a seat rail.

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