EP2364378B1 - Products in aluminium-copper-lithium alloy - Google Patents

Description

Field of the invention

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

State of the art

A continuous research effort is being made to develop materials that can simultaneously reduce the weight and increase the efficiency of high performance aircraft structures. 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. For these alloys to be selected in aircraft, their performance must reach that of commonly used alloys, in particular in terms of a compromise between the static mechanical strength properties (elastic limit, breaking strength) and the properties of damage tolerance ( toughness, resistance to the propagation of fatigue cracks), these properties being in general antinomic. 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.

The patent US 5,032,359 discloses a large 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 under the trade name "Weldalite ™".

The patent US 5,198,045 discloses a family of Weldalite ™ alloys comprising (in% by weight) (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 a compromise between strength and toughness of interest.

The patent US 7,229,509 discloses a family of Weldalite ™ alloys comprising (in% 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, (up to 0.4) Zr or other affinants such as Cr, Ti, Hf, Sc and V. The examples presented 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 non-zirconium-containing Weldalite ™ alloy for fuselage plates comprising (in% by weight) (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 patent EP1891247 discloses a Weldalite ™ alloy which is lightly loaded with alloying elements and is also intended for the manufacture of fuselage sheets comprising (in% by weight) (2.7-3.4) Cu, (0.8-1.4) Li (0.2-0.6) Mg, (0.1-0.8) Ag and at least one member selected from Zr, Mn, Cr, Sc, Hf, Ti.

The patent application WO2006 / 131627 discloses an alloy for fuselage plates comprising (in% by weight) (2.7-3.4) Cu, (0.8-1.4) Li, (0.2-0.6) Mg, ( 0.1-0.8) Ag and at least one of Zr, Mn, Cr, Sc, Hf and Ti, wherein the Cu and Li contents are Cu + 5/3 Li <5.2 .

The patent US5,455,003 discloses a process for producing aluminum-copper-lithium alloys having improved mechanical strength and toughness properties at cryogenic temperature. This method applies in particular to an alloy comprising (in% by weight) (2.0-6.5) Cu, (0.2-2.7) Li, (0-4.0) Mg, (0- 4.0) Ag, (0-3.0) Zn.

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

It has been generally accepted in these patents or patent applications that thorough homogenization, that is to say at a temperature of at least 527 ° C. and for a duration of at least 24 hours, makes it possible to reach the optimal properties of the alloy. In some cases of light alloys ( EP1891247 ) or free of zirconium ( WO2007 / 080267 ), much less thorough homogenization conditions, that is to say at a temperature below 510 ° C, were used.

However, there is still a need for low density Al-Cu-Li alloy products and further improved properties, particularly in terms of the compromise between mechanical strength on the one hand, and damage tolerance, and in particular the toughness and resistance to the propagation of fatigue cracks, on the other hand, while having other properties of satisfactory use, including corrosion resistance.

Object of the invention

1. a) on élabore un bain de métal liquide comprenant 2,0 à 3,5 % en poids de Cu, 1,4 à 1,8 % en poids de Li, 0,1 à 0,5 % en poids d'Ag, 0,1 à 1,0 % en poids de Mg, 0,05 à 0,18 % en poids de Zr, 0,2 à 0,6 % en poids de Mn et au moins un élément choisi parmi Cr, Sc, Hf et Ti, la quantité dudit élément, s'il est choisi, étant de 0,05 à 0,3 % en poids pour Cr et pour Sc, 0,05 à 0,5 % en poids pour Hf et de 0,01 à 0,15 % en poids pour Ti,
   le reste étant de l'aluminium et des impuretés inévitables ;
2. b) on coule une forme brute à partir dudit bain de métal liquide ;
3. c) on homogénéise ladite forme brute à une température comprise entre 515 °C et 525°C de façon à ce que le temps équivalent pour l'homogénéisation $$\mathrm{t}\left(\mathrm{eq}\right)=\frac{\int \exp \left(-\mathrm{26100}/\mathrm{T}\right)\mathrm{dt}}{\exp \left(-\mathrm{26100}/{\mathrm{T}}_{\mathrm{ref}}\right)}$$
   
   soit compris entre 5 et 20 heures, où T (en Kelvin) est la température instantanée de traitement, qui évolue avec le temps t (en heures), et T_ref est une température de référence fixée à 793 K ;
4. d) on déforme à chaud et optionnellement à froid ladite forme brute en un produit filé, laminé et/ou forgé ;
5. e) on met en solution et on trempe ledit produit ;
6. f) on tractionne de façon contrôlée ledit produit avec une déformation permanente de 1 à 5 % et préférentiellement d'au moins 2% ;
7. g) on réalise un revenu dudit produit par chauffage à 140 à 170 °C pendant 5 à 70 heures de façon à ce que ledit produit ait une limite d'élasticité conventionnelle mesurée à 0,2% d'allongement d'au moins 440 MPa et de préférence d'au moins 460 MPa.

The invention defined according to claim 1 relates to a process for manufacturing a spun, rolled and / or forged aluminum alloy product in which:

1. a) a bath of liquid metal comprising 2.0 to 3.5% by weight of Cu, 1.4 to 1.8% by weight of Li, 0.1 to 0.5% by weight of Ag is prepared, 0.1 to 1.0% by weight of Mg, 0.05 to 0.18% by weight of Zr, 0.2 to 0.6% by weight of Mn and at least one element selected from Cr, Sc, Hf and Ti, the amount of said 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,
   the rest being aluminum and unavoidable impurities;
2. b) pouring a raw form from said bath of liquid metal;
3. c) homogenizing said crude form at a temperature between 515 ° C and 525 ° C so that the equivalent time for homogenization $$\mathrm{t}\left(\mathrm{eq}\right)=\frac{\int \exp \left(-\mathrm{26100}/\mathrm{T}\right)\mathrm{dt}}{\exp \left(-\mathrm{26100}/{\mathrm{T}}_{\mathrm{ref}}\right)}$$
   
   is between 5 and 20 hours, where T (in Kelvin) is the instantaneous treatment temperature, which changes with time t (in hours), and T _ref is a reference temperature set at 793 K;
4. d) hot deformed and optionally cold deformed said raw form into a product spun, rolled and / or forged;
5. e) the solution is dissolved and quenched;
6. f) controlled pulling said product with a permanent deformation of 1 to 5% and preferably at least 2%;
7. g) an income of said product is obtained 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 of at least 440 MPa and preferably at least 460 MPa.

The invention also relates to a product spun, rolled and / or forged aluminum alloy with a density of less than 2.67 g / cm ³ obtainable by the process according to the invention.

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 Example 1. The dimensions are given in mm. The samples used for the mechanical characterizations were taken from the area indicated by the dots. The thickness of the sole is 16 mm.
• Figure 2 . Shape of the profile X of Example 2. The dimensions are given in mm. The thickness of the sole is 26.3 mm.
• Figure 3 . Form Y profile of Example 2. The dimensions are given in mm. The thickness of the sole is 18 mm.
• Figure 4 . Compromise between toughness and mechanical strength obtained for the X profiles of Example 2.
• Figure 5 . Compromise between toughness and mechanical strength obtained for the Y profiles of Example 2; 5a: sole and long direction; 5b: sole and long cross.
• Figure 6 . Wohler curve of fatigue crack initiation for the Y profiles of Example 2.
• Figure 7 . Shape of the profile Z of Example 3. The dimensions are given in mm. The samples used for the mechanical characterizations were taken from the area indicated by the dots. The thickness of the sole is 20 mm.
• Figure 8 . Form of the profile P of Example 4. The dimensions are given in mm.
• Figure 9 . Shape of the profile Q of Example 5. The dimensions are given in mm.

Description of the invention

Unless stated otherwise, all the information concerning the chemical composition of the alloys is expressed as a percentage by weight based on the total weight of the alloy. The designation of alloys is 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.

Unless otherwise stated, the static mechanical characteristics, in other words the _ultimate tensile strength R _m , the conventional yield stress at 0.2% elongation R _p0.2 ("yield strength") and the 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 EN 485-1 standard.
The stress intensity factor (K _Q ) is determined according to ASTM E 399. Thus, the proportion of specimens defined in paragraph 7.2.1 of this standard is always and the general procedure defined in paragraph 8. The ASTM E 399 standard provides in 9.1.3 and 9.1.4 criteria for determining whether K _Q is a valid K _{1C value} . Thus, a value K _1C is always a value K _Q the reciprocal is not true. In the context of the invention, the criteria of paragraphs 9.1.3 and 9.1.4 of ASTM E399 are not always checked, however for a given specimen geometry, the K _Q values presented are always comparable to each other. , the specimen geometry to obtain a valid value of K _1C is not always accessible given the constraints related to the dimensions of the sheets or profiles.

The MASTMAASIS (Modified ASTM Acetic Acid Salt Intermittent Spray) test is performed according to ASTM G85.
Unless otherwise specified, the definitions of EN 12258 apply. 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.

Here, 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. For an aircraft, 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 (stiffeners), ribs (ribs) and spars) and empennage including horizontal stabilizers and vertical stabilizers horizontal or vertical stabilizers, as well as floor beams, seat tracks and doors.

où T (en Kelvin) est la température instantanée de traitement, qui évolue avec le temps t (en heures), et T_ref est une température de référence fixée à 793 K. t(eq) est exprimé en heures. La constante Q/R = 26100 K est dérivée de l'énergie d'activation pour la diffusion du Mn, Q = 217000 J/mol. La formule donnant t(eq) tient compte des phases de chauffage et de refroidissement. Dans le mode de réalisation préféré de l'invention, la température d'homogénéisation est d'environ 520 °C et la durée de traitement est comprise entre 8 et 20 heures. Pour l'homogénéisation, les temps indiqués correspondent à des durées pour lesquelles le métal est effectivement à la température souhaitée.The present inventors have found that, surprisingly, for certain low density Al-Cu-Li alloys containing at the same time an addition of silver, magnesium, zirconium and manganese, the choice of specific homogenization conditions makes it possible to significantly improve the compromise between mechanical resistance and damage tolerance.
The method according to the invention allows the manufacture of a product spun, rolled and / or forged. In a first step, a bath of liquid metal is produced so as to obtain an aluminum alloy of defined composition.
The copper content of the alloy for which the surprising effect related to the choice of homogenization conditions is observed is between 2.0 and 3.5% by weight, preferably between 2.45 or 2.5 and 3.3% by weight. In an advantageous embodiment, the copper content is between 2.7 and 3.1% by weight.
The lithium content is between 1.4 and 1.8%. In an advantageous embodiment, the lithium content is between 1.42 and 1.77% by weight.
The silver content is between 0.1 and 0.5% by weight. The present inventors have found that a significant amount of silver is not needed to achieve the desired improvement in the trade-off between strength and damage tolerance. In an advantageous embodiment of the invention, 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 magnesium content is between 0.1 and 1.0% by weight and preferably it is less than 0.4% by weight.
The combination of specific homogenization conditions and the simultaneous addition of zirconium and manganese is an essential feature of the invention. The zirconium content must be between 0.05 and 0.18% by weight and the manganese content must be between 0.2 and 0.6% by weight. Preferably, the manganese content is at most 0.35% by weight.
The alloy also contains at least one element that can contribute to the control of the grain size selected from Cr, Sc, Hf and Ti, the quantity of the element, if it is chosen, being 0.05 to 0.3% by weight for Cr and for Sc, 0.05 to 0.5% by weight for Hf and 0.01 to 0.15% by weight for Ti.
It is preferable to limit the content of unavoidable impurities in the alloy so as to achieve the most favorable damage tolerance properties. The unavoidable impurities include iron and silicon, these impurities preferably have a content of less than 0.08% by weight and 0.06% by weight for iron and silicon, respectively, the other impurities preferably have a lower content to 0.05% by weight each and 0.15% by weight in total. Moreover, the zinc content is preferably less than 0.04% by weight.
Preferably, the composition is adjusted so as to obtain a density at room temperature of less than 2.67 g / cm ³ , even more preferably less than 2.66 g / cm ^3, in some cases even less than 2.65 g / cm ³ or even 2.64 g / cm ³ . The decrease in density is generally associated with a degradation of the properties. In the context of the invention, it is possible surprisingly to combine a low density with a compromise of very advantageous mechanical properties.
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 515 ° C. and 525 ° C. so that the equivalent time t (eq) at 520 ° C. for homogenization is between 5 and 20 hours and preferably between 6 and 20 hours. and 15 hours. The equivalent time t (eq) at 520 ° C is defined by the formula: $$\mathrm{t}\left(\mathrm{eq}\right)=\frac{\int \exp \left(-\mathrm{26100}/\mathrm{T}\right)\mathrm{dt}}{\exp \left(-\mathrm{26100}/{\mathrm{T}}_{\mathrm{ref}}\right)}$$

where T (in Kelvin) is the instantaneous treatment temperature, which changes with time t (in hours), and T _ref is a reference temperature set at 793 K. t (eq) is expressed in hours. The constant Q / R = 26100 K is derived from the activation energy for the diffusion of Mn, Q = 217000 J / mol. The formula giving t (eq) takes into account the heating and cooling phases. In the preferred embodiment of the invention, the homogenization temperature is about 520 ° C and the treatment time is between 8 and 20 hours. For homogenization, the times indicated correspond to times for which the metal is actually at the desired temperature.

1. (a) sa limite d'élasticité conventionnelle mesurée à 0,2% d'allongement dans le sens L R_p0,2(L) exprimée en MPa et sa ténacité K_1C(L-T), dans le sens L-T exprimée en MPa $\sqrt{\mathrm{m}}$
   
   sont telles que K_Q(L-T) > 129 - 0,17 R_p0,2(L), préférentiellement K_Q(L-T) > 132 - 0,17 R_p0,2(L) et encore plus préférentiellement K_Q(L-T) > 135 - 0,17 R_p0,2(L) ; et/ou
2. (b) sa résistance à la rupture dans le sens L R_m(L) exprimée en MPa et sa ténacité K_Q(L-T), dans le sens L-T exprimée en MPa $\sqrt{\mathrm{m}}$
   
   sont telles que K_Q(L-T) > 179 - 0,25 R_m(L), préférentiellement K_Q(L-T) > 182 - 0,25 R_m(L) et encore plus préférentiellement K_Q(L-T) > 185 - 0,25 R_m(L) ; et/ou
3. (c) sa résistance à la rupture dans le sens TL R_m(TL) exprimée en MPa et sa ténacité K_Q(L-T), dans le sens L-T exprimée en MPa $\sqrt{\mathrm{m}}$
   
   sont telles que K_Q(L-T) > 88 - 0,09 R_m(TL), préférentiellement K_Q(L-T) > 90 - 0,09 R_m(TL) et encore plus préférentiellement K_Q(L-T) > 92 - 0,09 R_m(TL) et/ou
4. (d) sa limite d'élasticité conventionnelle mesurée à 0,2% d'allongement dans le sens L R_p0,2(L) d'au moins 490 MPa et de préférence d'au moins 500 MPa et sa contrainte maximale pour l'initiation des fissures de fatigues pour un nombre de cycles à rupture de 10⁵ est supérieure à 210 MPa, préférentiellement supérieure à 220 MPa et encore plus préférentiellement supérieure à 230 MPa pour des éprouvettes de Kt = 2,3, avec R = 0,1.

De manière préférée, la ténacité K_Q(L-T) des produits filés selon l'invention est d'au moins 43 MPa $\sqrt{\mathrm{m}}\mathrm{.}$

In the examples, it is shown that the homogenization conditions according to the invention make it possible to improve, surprisingly, the compromise between toughness and mechanical strength with respect to conditions in which the combination of duration and temperature is lower or higher. It is generally accepted by those skilled in the art that, in order to minimize the homogenization time, it is advantageous to carry out the homogenization at the highest possible temperature so as to avoid local melting so as to accelerate the scattering of elements and precipitation of dispersoids. The present inventors have found on the contrary for the alloy composition according to the invention, a surprising favorable effect of a combination of duration and homogenization temperature lower than that according to the prior art.
After homogenization, the raw form is generally cooled to room temperature before being preheated for hot deformation. Preheating aims to reach a temperature preferably between 400 and 500 ° C and preferably of the order of 450 ° C allowing the deformation of the raw form. Preheating is typically 20 hours at 520 ° C for plates. It should be noted that, unlike homogenization, the times and temperatures mentioned for preheating correspond to the time spent in the oven and the temperature of the oven and not to the temperature actually reached by the metal and the time spent in this oven. temperature. For billets to be spun, induction preheating is advantageous.
Hot deformation and optionally cold deformation is typically performed by spinning, rolling and / or forging to obtain a spun, rolled and / or forged product. The product thus obtained is then put in solution preferably by heat treatment between 490 and 530 ° C for 15 min to 8 h, then typically quenched with water at room temperature or preferably cold water.
The product then undergoes a controlled pull of 1 to 5% and preferably of at least 2%. In one embodiment of the invention, cold rolling is carried out with a reduction of between 5% and 15% before the controlled pulling step. Known steps such as planing, straightening, shaping may optionally be performed before or after the controlled pull.
An income is made at a temperature between 140 and 170 ° C for 5 to 70 hours so that the product has a conventional yield strength measured at 0.2% an elongation of at least 440 MPa and preferably at least 460 MPa. The present inventors have found that, surprisingly, the combination of the homogenization conditions according to the invention with a preferred income achieved by heating at 148 to 155 ° C. for 10 to 40 hours makes it possible in certain cases to reach a level of toughness. K _1C (LT) particularly high.
The present inventors believe that the products obtained by the process according to the invention have a very particular microstructure, although they have not yet been able to describe it precisely. In particular, the size, the distribution and the morphology of the dispersoids containing manganese seem to be remarkable for the products obtained by the process according to the invention, however the complete characterization of its dispersoids, whose size is of the order of 50 to 100 nm, requires observations in electron microscopy at a magnification of x 30 000, quantified and numerous which explains the difficulty of obtaining a reliable description.
The products according to the invention preferably have a substantially non-recrystallized granular structure. By essentially non-recrystallized it is understood that at least 80% and preferably at least 90% of the grains are not recrystallized at quarter and mid-product thickness.
The spun products and in particular the extruded profiles obtained by the process according to the invention are particularly advantageous. The advantages of the method according to the invention have been observed for thin sections whose thickness of at least one elementary rectangle is between 1 mm and 8 mm and thick sections, however the thick sections, that is to say ie whose thickness of at least one elementary rectangle is greater than 8 mm, and preferably greater than 12 mm, or even 15 mm are the most advantageous. The compromise between the static mechanical strength and the toughness or the fatigue strength is particularly advantageous for the spun products according to the invention.
An aluminum alloy spun product according to the invention has a density of less than 2.67 g / cm ³ , is obtainable by the process according to the invention, and is advantageously characterized in that:

1. (a) its conventional yield strength measured at 0.2% LR _{elongation p0.2} (L) expressed in MPa and its toughness K _1C (LT), in the LT direction expressed in MPa $\sqrt{\mathrm{m}}$
   
   are such that K _Q (LT)> 129 - 0.17 R _p0.2 (L), preferentially K _Q (LT)> 132 - 0.17 R _p0.2 (L) and even more preferably K _Q (LT) > 135 - 0.17 R _p0.2 (L); and or
2. (b) its breaking strength in the LR _m (L) direction expressed in MPa and its tenacity K _Q (LT), in the LT direction expressed in MPa $\sqrt{\mathrm{m}}$
   
   are such that K _Q (LT)> 179 - 0.25 R _m (L), preferably K _Q (LT)> 182 - 0.25 R _m (L) and even more preferably K _Q (LT)> 185 - 0 R _m (L); and or
3. (c) its tensile strength in the TL R _m (TL) direction expressed in MPa and its tenacity K _Q (LT), in the LT direction expressed in MPa $\sqrt{\mathrm{m}}$
   
   are such that K _Q (LT)> 88 - 0.09 R _m (TL), preferably K _Q (LT)> 90 - 0.09 R _m (TL) and even more preferably K _Q (LT)> 92 - 0 , 09 R _m (TL) and / or
4. (d) its conventional yield strength measured at 0.2% LR _{elongation p0.2} (L) of at least 490 MPa and preferably at least 500 MPa and its maximum stress for the initiation of fatigue cracks for a number of rupture cycles of 10 ⁵ is greater than 210 MPa, preferably greater than 220 MPa and even more preferably greater than 230 MPa for specimens of Kt = 2.3, with R = 0.1 .

Preferably, toughness K _Q (LT) of the extruded products according to the invention is at least 43 MPa $\sqrt{\mathrm{m}}\mathrm{.}$

avec une limite d'élasticité R_p0,2(L) d'au moins 490 MPa, ou préférentiellement une ténacité K_Q(L-T) d'au moins 56 MPa $\sqrt{\mathrm{m}}$

avec une résistance à rupture R_m(L) d'au moins 515 MPa, une teneur en cuivre comprise entre 2,45 et 2,65 % en poids est associée à une teneur en lithium comprise entre 1,4 et 1,5 % en poids.In the embodiment of the invention, achieving for spun products a toughness K _Q (LT) of at least 52 MPa $\sqrt{\mathrm{m}}$

with a yield strength R _p0.2 (L) of at least 490 MPa, or preferably a K _Q (LT) toughness of at least 56 MPa $\sqrt{\mathrm{m}}$

with a breaking strength R _m (L) of at least 515 MPa, a copper content of between 2.45 and 2.65% by weight is associated with a lithium content of between 1.4 and 1.5% in weight.

avec une limite d'élasticité R_p0,2(L) d'au moins 520 MPa, une teneur en cuivre comprise entre 2,65 et 2,85 % en poids est associée à une teneur en lithium comprise entre 1,5 et 1,7 % en poids.
De manière préférée, la densité des produits filés selon l'invention est inférieure à 2,66 g/cm³, de manière encore plus préférée inférieure à 2,65 g/cm³ voire dans certains cas inférieure à 2,64 g/cm³.In another embodiment of the invention, it is possible to achieve, for spun products, a toughness K _Q (LT) of at least MPa $\sqrt{\mathrm{m}}$

with a yield strength R _p0.2 (L) of at least 520 MPa, a copper content of between 2.65 and 2.85% by weight is associated with a lithium content of between 1.5 and 1 , 7% by weight.
Preferably, the density of the spun products according to the invention is less than 2.66 g / cm ³ , even more preferably less than 2.65 g / cm ^3, in some cases even less than 2.64 g / cm 3. ³ .

sont alors telles R_m(L) > 550 et K_Q(L-T) > 50.
Le procédé selon l'invention permet également d'obtenir des produits laminés avantageux. Parmi les produits laminés, les tôles dont l'épaisseur est au moins de 10 mm et de préférences d'au moins 15 mm et/ou au plus 100 mm et de préférence au plus 50 mm sont avantageuses.
Un produit laminé en alliage d'aluminium selon l'invention a une densité inférieure à 2,67 g/cm³, est susceptible d'être obtenu par le procédé selon l'invention, et est avantageusement caractérisé en ce que sa ténacité K_Q(L-T), dans le sens L-T est au moins de 23 MPa $\sqrt{\mathrm{m}}$

et de préférence d'au moins 25 MPa $\sqrt{\mathrm{m}},$

sa limite d'élasticité conventionnelle mesurée à 0,2% d'allongement dans le sens L R_p0,2(L) est au moins égale à 560 MPa et de préférence au moins égale à 570 MPa et/ou sa résistance à la rupture dans le sens L R_m(L) est au moins égale à 585 MPa et de préférence au moins égale à 595 MPa.
De manière préférée, la densité des produits laminés selon l'invention est inférieure à 2,66 g/cm³, de manière encore plus préférée inférieure à 2,65 g/cm³ voire dans certains cas inférieure à 2,64 g/cm³.
Les produits selon l'invention peuvent de manière avantageuse être utilisés dans des éléments de structure, en particulier d'avion. Un élément de structure incorporant au moins un produit selon l'invention ou fabriqué à partir d'un tel produit est avantageux, en particulier pour la construction aéronautique. Un élément de structure, formé d'au moins un produit selon l'invention, en particulier d'un produit filé selon l'invention utilisé en tant que raidisseur ou de cadre, peut être utilisé avantageusement pour la fabrication de panneaux de fuselage ou de voilure d'avions de même que toute autre utilisation où les présentes propriétés pourraient être avantageuses.
Dans l'assemblage de pièces structurales, toutes les techniques connues et possibles de rivetage et de soudage appropriées pour des alliages en aluminium peuvent être utilisées, si souhaité. Les inventeurs ont trouvé que si le soudage est choisi, il peut être préférable d'utiliser des techniques de soudage au laser ou de soudage par friction-malaxage.
Les produits de l'invention n'induisent généralement aucun problème particulier pendant des opérations ultérieures de traitement de surface classiquement utilisées en construction aéronautique.
La résistance à la corrosion des produits de l'invention est généralement élevée ; à titre d'exemple, le résultat au test MASTMAASIS est au moins EA et de préférence P pour les produits selon l'invention.
Ces aspects, ainsi que d'autres de l'invention sont expliqués plus en détail à l'aide des exemples illustratifs et non limitant suivants.In an advantageous embodiment of the invention, an income is obtained which makes it possible to obtain a conventional yield strength measured at 0.2% elongation greater than 520 MPa, for example from 30 h to 152 ° C., the resistance at break in the LR _m (L) direction, expressed in MPa and the K _Q toughness (LT), in the LT direction expressed in MPa $\sqrt{\mathrm{m}}$

are then such R _m (L)> 550 and K _Q (LT)> 50.
The process according to the invention also makes it possible to obtain advantageous rolled products. Among the rolled products, the sheets whose thickness is at least 10 mm and preferably at least 15 mm and / or at most 100 mm and preferably at most 50 mm are advantageous.
An aluminum alloy laminated product according to the invention has a density of less than 2.67 g / cm ³ , is obtainable by the method according to the invention, and is advantageously characterized in that its tenacity K _Q (LT), in the LT direction is at least 23 MPa $\sqrt{\mathrm{m}}$

and preferably at least 25 MPa $\sqrt{\mathrm{m}},$

its conventional yield strength measured at 0.2% elongation in the LR _p0.2 (L) direction is at least 560 MPa and preferably at least 570 MPa and / or its breaking strength in the direction LR _m (L) is at least 585 MPa and preferably at least equal to 595 MPa.
Preferably, the density of the rolled products according to the invention is less than 2.66 g / cm ³ , even more preferably less than 2.65 g / cm ^3, in some cases even less than 2.64 g / cm 3. ³ .
The products according to the invention can advantageously be used in structural elements, in particular aircraft. 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. A structural element, formed of at least one product according to the invention, in particular a spun product according to the invention used as stiffener or frame, can be advantageously used for the manufacture of fuselage panels or airplane wing as well as any other use where the present properties could be advantageous.
In the assembly of structural parts, all known and possible riveting and welding techniques suitable for aluminum alloys can be used, if desired. The inventors have found that if welding is chosen, it may be preferable to use laser welding or friction stir welding techniques.
The products of the invention generally do not induce any particular problem during subsequent surface treatment operations conventionally used in aeronautical construction.
The corrosion resistance of the products of the invention is generally high; for example, the MASTMAASIS test result is at least EA and preferably P for the products according to the invention.
These and other aspects of the invention are explained in more detail with the aid of the following illustrative and non-limiting examples.

Examples Example 1

In this example, several plates Al-Cu-Li alloy whose composition is given in Table 1 were cast. Table 1. Composition in% by weight and density of Al-Cu-Li alloys used Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 1 0.06 0.04 2.94 0.01 0.36 0.01 0.02 0.12 1.62 0.34 2,635 2 0.04 0.05 2.83 0.33 0.36 0.02 0.02 0.11 1.59 0.38 2,641

The plates were homogenized according to the prior art for 8 h at 500 ° C. and then 24h at 527 ° C. Bills were taken from the plates. The billets were heated to 450 ° C +/- 40 ° C and then hot spun to obtain W profiles according to Figure 1 . The profiles thus obtained were dissolved at 524 ° C, quenched with water temperature below 40 ° C, and tractionned with a permanent elongation of between 2 and 5%. The income was made for 48 hours at 152 ° C. Samples taken at the end of the profile were tested for their static mechanical properties (elastic limit R _p0,2 , the tensile strength R _m , and the elongation at break (A), diameter of the samples: 10 mm) as well as their toughness (K _Q ). The location of the samples is indicated in dotted lines on the Figure 1 . The specimens used for the tenacity measurements had B = 15 mm and W = 30 mm.

R_m (MPa) R_p0,2 (MPa) A (%) R_m (MPa) R_p0,2 (MPa) A (%) L-T T-L 1 571 533 8,7 560 508 10,4 28,5 29,0 2 556 522 7,9 550 515 8,4 37,6 35,5 A temperature rise rate of 15 ° C / h and 50 ° C / h were used for homogenization and dissolution, respectively. The equivalent time for homogenization was 37.5 hours.
The results obtained are given in Table 2 below. Table 2. Mechanical properties of the profiles obtained from alloys 1 and 2. Alloy Meaning L Meaning of LT K _Q (K _1C ) $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

R _m (MPa) R _p0.2 (MPa) AT (%) R _m (MPa) R _p0.2 (MPa) AT (%) LT TL 1 571 533 8.7 560 508 10.4 28.5 29.0 2 556 522 7.9 550 515 8.4 37.6 35.5

Example 2

In this example, three homogenization conditions were compared for two types of profiles, obtained from billets taken from a plate whose composition is given in Table 3 below. Table 3 Composition in% by weight and density of the Al-Cu-Li alloy used. Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 3 0.03 0.04 2.72 0.31 0.31 0.02 0.03 0.10 1.61 0.34 2,637

The billets were homogenized either 8h at 500 ° C and then 24h at 527 ° C (reference A) or 8h at 520 ° C (reference B) or 8h at 500 ° C (reference C). The rate of rise in temperature was 15 ° C / h for the homogenization and the equivalent time was 37.5 hours for homogenization of reference A, 9.5 hours for homogenization of reference B, and 4 After homogenization, the billets were heated to 450 ° C. +/- 40 ° C. and then hot-spun to obtain X-profiles according to FIG. Figure 2 or Y according to the Figure 3 . The profiles thus obtained were dissolved at 524 +/- 2 ° C, quenched with water temperature below 40 ° C, and tractionned with a permanent elongation of between 2 and 5%.

R_m (MPa) R_p0,2 (MPa) A (%) R_m (MPa) R_p0,2 (MPa) A (%) L-T T-L 48H152°C A 563 533 8,4 512 484 5,4 39,1 30,9 B 569 541 9,8 528 500 6,6 40,7 34,2 C 565 537 7,7 507 477 6,7 37,7 28,9 30h152°C A 554 522 8,8 500 470 5,2 42,5 34,1 B 557 524 10,1 519 486 7,4 53,3 42,9 C 553 520 8,0 494 457 7,4 40,7 32,9 23h145°C A 512 452 9,3 448 390 6,7 47,2 43,8 B 515 455 10,0 479 414 12,6 47,1 58,9 C 513 454 8,3 445 377 9,0 45,6 43,2 Different income conditions have been implemented. Samples taken at the end of the section were tested for their static mechanical properties (elastic limit R _p0,2 , the tensile strength R _m , and the elongation at break (A) as well as their toughness ( K _Q ) The sampling zones for the Y profile are indicated on the Figure 3 : reinforcement (1), reinforcement / sole (2) sole (3), the specimens used for the tenacity measurements had characteristics B = 15 mm and W = 60 mm. For the X profile, the samples are taken on the sole, the specimens used for the tenacity measurements had characteristics B = 20 mm and W = 76 mm. Samples taken had a diameter of 10 mm except for the TL direction for which the samples had a diameter of 6 mm.
The results obtained on the X profiles are given in Table 4 below. Table 4. Mechanical properties of alloy X sections 3. Returned homogenization Meaning L TL direction K _Q $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

R _m (MPa) R _p0.2 (MPa) AT (%) R _m (MPa) R _p0.2 (MPa) AT (%) LT TL 48H152 ° C AT 563 533 8.4 512 484 5.4 39.1 30.9 B 569 541 9.8 528 500 6.6 40.7 34.2 VS 565 537 7.7 507 477 6.7 37.7 28.9 30h152 ° C AT 554 522 8.8 500 470 5.2 42.5 34.1 B 557 524 10.1 519 486 7.4 53.3 42.9 VS 553 520 8.0 494 457 7.4 40.7 32.9 23h145 ° C AT 512 452 9.3 448 390 6.7 47.2 43.8 B 515 455 10.0 479 414 12.6 47.1 58.9 VS 513 454 8.3 445 377 9.0 45.6 43.2

These results are illustrated by the Figures 4a (L direction) and 4b (TL direction). For the profiles from billet having been homogenized at 520 ° C, the compromise between strength and toughness is very much improved. In the long sense, the improvement is particularly clear for a 30 hour income at 152 ° C.

L-T 34,3 45,2 30,5 42,8 T-L 29,3 42,5 26,4* 37,3 * K_1C The results obtained with the Y profile are given in Table 5 below. Table 5. Mechanical properties of alloy Y sections 3. Returned 30h 152 ° C 48h 152 ° C homogenization AT B AT B sense L - Reinforcement R _m (MPa) 527 563 538 573 R _p0.2 (MPa) 500 537 516 551 AT (%) 7.5 9.9 8.1 9.6 L-reinforcement / sole R _m (MPa) 534 580 551 590 R _p0.2 (MPa) 510 559 534 572 AT (%) 6.6 8.6 7 7.8 sense L - Sole R _m (MPa) 543 536 557 549 R _p0.2 (M Pa) 505 494 529 517 AT (%) 7.3 9.2 7.2 9.5 TL direction (sole) R _m (MPa) 501 488 513 503 R _p0.2 (MPa) 456 441 472 462 AT (%) 8.8 12.3 8.6 11.4 K _Q (CT15-W60) $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

LT 34.3 45.2 30.5 42.8 TL 29.3 42.5 26.4 * 37.3 * K _1C

These results are illustrated by the Figures 5a (L direction) and 5b (TL direction). For profiles from billets that have been homogenized at 520 ° C, the compromise between strength and toughness is again very much improved for the two tested income conditions.

Fatigue tests were carried out in the case of the 30 hr income at 152 ° C, on test tubes with hole (Kt = 2,3) with a ratio (minimum load / maximum load) R = 0,1 at a frequency of 80 Hz. The tests were carried out in the ambient air of the laboratory. These tests are presented on the Figure 6 . For a given number of cycles, the increase in the maximum stress is between 10 and 25%. The maximum stress for the initiation of fatigue cracks for a number of failure cycles of 10 ⁵ is of the order of 230 MPa for specimens of Kt = 2.3, with R = 0.1.

Example 3

In this example, two of the homogenization conditions of Example 2 were compared for another type of profile, obtained from billets taken from a plate whose composition is given in Table 6 below: Table 6. Composition in% by weight of Al-Cu-Li alloys used Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 4 0.03 0.05 3.05 0.01 0.39 0.01 0.03 0.12 1.70 0.35 2,631 5 0.03 0.04 2.90 0.31 0.40 0.01 0.03 0.1 1.67 0.38 2,635

The alloy billets 4 were homogenized for 8 hours at 500 ° C. and then 24h at 527 ° C. (ie the reference homogenization A) while the alloy billets 5 were homogenized for 8 hours at 520 ° C. (reference B). After homogenization, the billets were heated to 450 ° C +/- 40 ° C and then hot spun to obtain Z profiles according to the Figure 7 . The profiles thus obtained were dissolved at 524 +/- 2 ° C, quenched with water temperature below 40 ° C, and tractionned with a permanent elongation of between 2 and 5%. The profiles finally had an income of 48h at 152 ° C. Samples taken at the end of the profile were tested for their static mechanical properties (elastic limit R _p0,2 , the tensile strength R _m , and the elongation at break (A), diameter of the samples: 10 mm), as well as their toughness (K _Q ), the specimens used for the toughness measurements had B = 15 mm and W = 60 mm. The measurements made at the end of the profile generally make it possible to obtain the most unfavorable mechanical characteristics of the profile. The location of the samples is indicated in dotted lines on the Figure 7 .

Alliage R_m (MPa) R_p0,2 (MPa) A (%) L-T T-L 4 576 527 8,4 31,0 31,4 5 574 536 9,8 38,2 37,8 The results obtained are given in Table 7 below. The products according to the invention have slightly higher mechanical characteristics and an improved toughness of more than 20%. Table 7. Mechanical properties of alloy Z profiles 4 and 5. Meaning L K _Q $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

Alloy R _m (MPa) R _p0.2 (MPa) AT (%) LT TL 4 576 527 8.4 31.0 31.4 5 574 536 9.8 38.2 37.8

Example 4

In this example, a billet whose composition is given in Table 8 was cast. Table 8 Composition in% by weight and density of the Al-Cu-Li alloy used. Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 6 0.03 0.05 3.1 0.3 0.4 0.01 0.03 0.11 1.65 0.34 2,639

The alloy billets 6 were homogenized for 8 hours at 520 ° C. (ie reference homogenization B). After homogenization, the billets were heated to 450 ° C. +/- 40 ° C. and then hot-spun to obtain P profiles according to Figure 8 . The profiles thus obtained were dissolved, quenched with water of temperature below 40 ° C, and tractionned with a permanent elongation of between 2 and 5%. The profiles finally had an income of 48h at 152 ° C. Samples taken at the end of the section were tested for their static mechanical properties (elastic limit R _p0,2 , the tensile strength R _m , and the elongation at break A).

The results obtained are given in Table 9 below. Table 9. Mechanical properties of alloy P profiles 6. Meaning L Alloy R _m (MPa) R _p0.2 (MPa) AT (%) 6 562 525 10.1

Fatigue tests were carried out in, on test pieces with a hole (Kt = 2.3) with a ratio (minimum load / maximum load) R = 0.1 at a frequency of 80 Hz. The tests were carried out at ambient air of the laboratory. The results of these tests are given in Table 10. Table 10. S / N fatigue test results for alloy profiles 6 Maximum load [MPa] cycles MPa NOT 300 22,120 280 31,287 260 46,696 240 53,462 220 87,648 200 113,583 180 132,003 170 203,112 160 232,743 150 177 733 140 5,113,237 130 9,338,654

Example 5

In this example, a billet whose composition is given in Table 11 was cast. Table 11 Composition in% by weight and density of the Al-Cu-Li alloy used. Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 7 0.03 0.05 3.1 0.3 0.4 0.01 0.04 0.10 1.71 0.36 2,636

The alloy billets 7 were homogenized for 8 hours at 520 ° C. (ie reference homogenization B). After homogenization, the billets were heated to 450 ° C +/- 40 ° C and then hot spun to obtain Q profiles according to the Figure 9 . The profiles thus obtained were dissolved, quenched with water of temperature below 40 ° C, and tractionned with a permanent elongation of between 2 and 5%. The profiles finally had an income of 48h at 152 ° C. Samples taken at the end of the section were tested for their static mechanical properties (elastic limit R _p0,2 , the tensile strength R _m , and the elongation at break A).

The results obtained are given in Table 12 below. Table 12. Mechanical properties of alloy Q sections 7. Alloy Meaning L R _m (MPa) R _p0.2 (MPa) AT (%) 7 561 521 8.5

Fatigue tests were carried out in, on test pieces with a hole (Kt = 2.3) with a ratio (minimum load / maximum load) R = 0.1 at a frequency of 80 Hz. The tests were carried out at ambient air of the laboratory. The results of these tests are given in Table 13. Table 13. S / N fatigue test results for alloy profiles 7. Maximum load [MPa] cycles MPa NOT 300 22,165 280 32,214 260 47,536 240 59,094 220 103,407 200 251,771 190 254,842 180 6,508,197 160 6,130,947 130 9,383,980

Example 6

In this example, a plate whose composition is given in Table 14 was cast. Table 14 Composition in% by weight and density of the Al-Cu-Li alloy used. Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 8 0.03 0.06 3.1 0.3 0.4 0.01 0.03 0.11 1.77 0.36 2,631

8 2,5 % 20 557 504 33,9 30 579 538 28,6 40 586 550 25,4 50 589 555 25,8* 8 4,4 % 20 577 543 30,5 30 589 562 27,2 40 594 566 23,8* 50 597 571 23,7 *K_1C The plate was scalped and then homogenized at 520 +/- 5 ° C for 8 h (the reference homogenization B). After homogenization, the plate was hot rolled to obtain sheets having a thickness of 25 mm. The sheets were put in solution at 524 +/- 2 ° C, quenched with cold water and triturated with a permanent elongation between 2 and 5%. Samples with a diameter of 10 mm taken from some of these sheets were then subjected to an income of between 20 h and 50 h at 155 ° C. These samples were tested to determine their static mechanical properties (yield strength R _p0,2 , breaking strength Rm, and elongation at break (A)) as well as their toughness (K _Q ), with specimens of geometry B = 15 mm, W = 30 mm. The results obtained are given in Table 15 below. Table 15 Mechanical properties of alloy plates 8 having undergone a laboratory income. Alloy Traction Duration of income at 155 ° C R _m L (MPa) R _p0.2 L (MPa) K _Q LT $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

8 2.5% 20 557 504 33.9 30 579 538 28.6 40 586 550 25.4 50 589 555 25.8 * 8 4.4% 20 577 543 30.5 30 589 562 27.2 40 594 566 23.8 * 50 597 571 23.7 * K _1C

K_Q T-L $\left(\mathrm{M}\mathrm{P}\mathrm{a}\sqrt{\mathrm{m}}\right)$

2,5 594 559 6 568 523 6 522 466 9 26,2 25,1 4 600 571 6 575 537 6 526 476 10 25,3 24,7 The sheets received an industrial income of 48 h at 152 ° C. The results of the mechanical tests (sampling at mid-thickness) carried out on the sheets thus obtained are given in Table 16. Table 16 Mechanical Properties of Alloyed 8 Industrial Plate Traction R _m L (MPa) R _p0.2 L (MPa) A% L R _m TL (MPa) R _p0.2 TL (MPa) A% TL R _m 45 ° (MPa) R _p0.2 45 ° (MPa) At% 45 ° K _Q LT $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

K _Q TL $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

2.5 594 559 6 568 523 6 522 466 9 26.2 25.1 4 600 571 6 575 537 6 526 476 10 25.3 24.7

Example 7

R_m (MPa) R_p0,2 (MPa) A (%) R_m (MPa) R_p0,2 (MPa) A (%) L-T T-L 9 20H 152 °C 468 405 12,6 444 388 15,1 60,8 60,2 30H 152 °C 497 450 12,8 465 417 14,1 63,7 52,1 48H 152 °C 517 478 11,0 486 447 12,5 60,3 47,9* 60H 152 °C 526 493 10,9 494 458 12,7 56,5 45,6* 10 20H 152 °C 488 433 10,9 457 397 13,1 61,4 54,1 30H 152 °C 513 470 11,3 486 441 13,2 59,8 47,7 48H 152 °C 532 498 10,1 501 463 12,4 55,2 42,5* 60H 152 °C 536 503 9,9 503 468 9,5 53,6 40,0* *K_1C Tableau 19. Propriétés mécaniques des profilés Y en alliage 8 et 9. Alliage Revenu Sens L Sens TL K_Q $\left(\mathrm{M}\mathrm{P}\mathrm{a}\sqrt{\mathrm{m}}\right)$

R_m (MPa) R_p0,2 (MPa) A (%) R_m (MPa) R_p0,2 (MPa) A (%) L-T T-L 9 20H 152 °C 489 432 12 451 392 15 53,6 53,6 30H 152 °C 517 477 11 478 435 13 57,9 50,8 48H 152 °C 535 501 10 494 457 12 56,9 47,2 60H 152 °C 539 506 10 497 462 12 53,0 45,4* 10 20H 152 °C 496 440 11,9 458 402 14 54,2 50,3 30H 152 °C 523 483 11,1 485 442 13 52,7 46,3 48H 152 °C 539 506 10,5 500 465 11 52,2 39,5 60H 152 °C 546 515 10,3 504 470 11 49,1 38,4* *K_1C In this example, the homogenization conditions according to the invention were used for two types of profiles, obtained from billets made of two different alloys whose composition is given in Table 17 below. Table 17 Composition in% by weight and density of the Al-Cu-Li alloy used. Alloy Yes Fe Cu mn mg Zn Ti Zr Li Ag Density (g / cm ³ ) 9 0.03 0.05 2.49 0.31 0.35 0.01 0.04 0.13 1.43 0.25 2,645 10 0.03 0.06 2.62 0.30 0.35 0.01 0.04 0.14 1.42 0.25 2,648 The billets were homogenized for 8 hours at 520 ° C. (reference B). The temperature rise rate was 15 ° C./h for homogenization and the equivalent time was 9.5 hours. After homogenization, the billets were reheated to 450 ° C. ° C +/- 40 ° C then hot spun to obtain X profiles according to the Figure 2 or Y according to the Figure 3 . The profiles thus obtained were dissolved at 524 +/- 2 ° C, quenched with water of temperature below 40 ° C, and tractionned with a permanent elongation of between 2 and 5%. Different income conditions have been implemented. Samples taken at the end of the section were tested for their static mechanical properties (elastic limit R _p0,2 , the tensile strength R _m , and the elongation at break (A) as well as their toughness ( K _Q ) Samples were taken from the soleplate for the X and Y sections.The samples taken had a diameter of 10 mm except for the TL direction for which the samples had a diameter of 6 mm. tenacity had characteristics B = 15 mm and W = 60 mm (Y profiles) and B = 20 mm and W = 76 mm (X profiles).
The results obtained on the X and Y sections are given in Tables 18 and 19 below. Alloy Returned Meaning L TL direction K _Q $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

R _m (MPa) R _p0.2 (MPa) AT (%) R _m (MPa) R _p0.2 (MPa) AT (%) LT TL 9 20H 152 ° C 468 405 12.6 444 388 15.1 60.8 60.2 30H 152 ° C four hundred ninety seven 450 12.8 465 417 14.1 63.7 52.1 48H 152 ° C 517 478 11.0 486 447 12.5 60.3 47.9 * 60H 152 ° C 526 493 10.9 494 458 12.7 56.5 45.6 * 10 20H 152 ° C 488 433 10.9 457 397 13.1 61.4 54.1 30H 152 ° C 513 470 11.3 486 441 13.2 59.8 47.7 48H 152 ° C 532 498 10.1 501 463 12.4 55.2 42.5 * 60H 152 ° C 536 503 9.9 503 468 9.5 53.6 40.0 * * K _1C Alloy Returned Meaning L TL direction K _Q $\left(\mathrm{M}\mathrm{P}\mathrm{at}\sqrt{\mathrm{m}}\right)$

R _m (MPa) R _p0.2 (MPa) AT (%) R _m (MPa) R _p0.2 (MPa) AT (%) LT TL 9 20H 152 ° C 489 432 12 451 392 15 53.6 53.6 30H 152 ° C 517 477 11 478 435 13 57.9 50.8 48H 152 ° C 535 501 10 494 457 12 56.9 47.2 60H 152 ° C 539 506 10 four hundred ninety seven 462 12 53.0 45.4 * 10 20H 152 ° C 496 440 11.9 458 402 14 54.2 50.3 30H 152 ° C 523 483 11.1 485 442 13 52.7 46.3 48H 152 ° C 539 506 10.5 500 465 11 52.2 39.5 60H 152 ° C 546 515 10.3 504 470 11 49.1 38.4 * * K _1C

et même supérieur à 55 MPa $\sqrt{\mathrm{m}}\mathrm{.}$

The compromise between toughness and mechanical strength obtained with alloys 9 and 10 is particularly advantageous, in particular to obtain very high toughness values, with K _Q (LT) greater than 50 MPa $\sqrt{\mathrm{m}},$

and even greater than 55 MPa $\sqrt{\mathrm{m}}\mathrm{.}$

Claims (15)

1. A method for manufacturing an extruded, laminated and / or forged product based on aluminum alloy, in which:

   a) a molten metal bath is prepared, comprising 2.0 to 3.1% by weight of Cu, 1.4 to 1.8% by weight of Li, 0.1 to 0.5% by weight of Ag, 0.1 to 1.0% by weight of Mg, 0.05 to 0.18% by weight of Zr, 0.2 to 0.6 % by weight of Mn and at least one element selected from Cr, Sc, Hf and Ti, the quantity of said element, if chosen being 0.05 to 0.3% by weight for Cr and Sc, 0.05 to 0.5 % by weight for Hf and 0.01 to 0.15% by weight for Ti, the remainder being aluminum and inevitable impurities, the composition being adjusted to obtain a density at room temperature of less than 2.67 g/cm³

   b) a rough shape is cast from said molten metal bath;

   c) said rough shape is homogenized at a temperature between 515 ° C and 525 ° C so that the equivalent time for homogenization $$\mathrm{t}\left(\mathrm{eq}\right)=\frac{\int \exp \left(-\mathrm{26100}/\mathrm{T}\right)\mathrm{dt}}{\exp \left(-\mathrm{26100}/{\mathrm{T}}_{\mathrm{ref}}\right)}$$

   

   is between 5 and 20 hours, where T (in Kelvin) is the instantaneous treatment temperature, which changes with time t (in hours), and T_ref is a reference temperature fixed at 793 K;

   d) said rough shape is hot and optionally cold worked to give an extruded, laminated and / or forged product

   e) said product undergoes solution heat treatment;

   f) said product undergoes controlled stretching with a permanent set of 1 to 5% and preferably at least 2%;

   g) said product is artificially aged by heating to 140-170° C for 5 to 70 hours so that said product has a conventional yield strength measured at 0.2% elongation of at least 440 MPa and preferably at least 460 MPa.
2. Process according to claim 1 in which the copper content of said molten metal bath is at least 2.5% by weight and preferably at least 2.7% in weight.
3. Process according to either of claims 1 to 2 in which the lithium content of said molten metal bath ranges between 1.42 and 1.77% by weight.
4. Process according to any of claims 1 to 3 in which said inevitable impurities include iron and silicon, these impurities having a content less than 0.08% by weight and 0.06% by weight for iron and silicon respectively, other impurities having a content less than 0.05% by weight each and 0.15% by weight in total.
5. Process according to any of claims 1 to 4 in which said equivalent time for homogenization ranges between 6 and 15 hours.
6. Process according to any of claims 1 to 5 in which the homogenization temperature is approximately 520°C and the treatment time is between 8 and 20 hours.
7. Process according to any of claims 1 to 6 in which said artificial aging is performed by heating to 148 to 155 °C for 10 to 40 hours.
8. Extruded product made of aluminum alloy of density less than 2.67 g/cm3 obtained by the process according to any of claims 1 to 7 characterized in that its fracture toughness KQ(L-T) is at least 52 $\mathrm{M}\mathrm{P}\mathrm{A}\mathrm{\surd m}$

   

   its yield strength R_p0,2(L) is at least 490 MPa, and in that its copper content is comprised between 2,45 and 2,65 weight % and its lithium content is comprised between 1,4 and 1,5 weight % and characterized in that:

   (a) its conventional yield strength measured at 0.2% elongation in direction L R_p0,2(L) expressed in MPa and its fracture toughness K_Q(L-T), in direction L-T expressed in MPa √m are such that K_Q(L-T) > 129 - 0,17 R_p0,2(L); and / or

   (b) its ultimate tensile strength in direction L R_m(L) expressed in MPa and its fracture toughness K_Q(L-T), in direction L-T expressed in MPa √m are such that $${\mathrm{K}}_{\mathrm{Q}}\left(\mathrm{L}-\mathrm{T}\right)>\mathrm{179}-\mathrm{0},\mathrm{25}{\mathrm{R}}_{\mathrm{m}}\left(\mathrm{L}\right),$$

   

   and / or

   (c) its ultimate tensile strength in direction LT R_m(LT) expressed in MPa and its fracture toughness K_Q(L-T), in direction L-T expressed in MPa √m are such that K_Q(L-T) > 88 - 0,09 R_m(LT), and / or

   (d) its conventional yield strength measured at 0.2% elongation in direction L R_p0,2(L) is at least 490 MPa and preferably at least 500 MPa and its maximum stress for the initiation of fatigue cracks for a number of cycles to break of 10⁵ is greater than 210 MPa for specimens with Kt = 2.3, with R = 0.1.
9. Extruded product according to claim 8 characterized in that its fracture toughness KQ(L-T) is at least 56 MPa√m and its ultimate tensile strength R_m (L) is at least 515 MPa.
10. Extruded product made of aluminum alloy of density less than 2.67 g/cm3 obtained by the process according to any of claims 1 to 7 characterized in that its fracture toughness K_Q(L-T) is at least 45 MPa√m its yield strength R_p0,2(L) is at least 520 MPa, and in that its copper content is comprised between 2,65 and 2,85 weight % and its lithium content is comprised between 1,5 and 1,7 weight % and characterized in that:

    (a) its conventional yield strength measured at 0.2% elongation in direction L R_p0,2(L) expressed in MPa and its fracture toughness K_Q(L-T), in direction L-T expressed in MPa √m are such that K_Q(L-T) > 129 - 0,17 R_p0,2(L); and / or

    (b) its ultimate tensile strength in direction L R_m(L) expressed in MPa and its fracture toughness K_Q(L-T), in direction L-T expressed in MPa √m are such that $${\mathrm{K}}_{\mathrm{Q}}\left(\mathrm{L}-\mathrm{T}\right)>\mathrm{179}-\mathrm{0},\mathrm{25}{\mathrm{R}}_{\mathrm{m}}\left(\mathrm{L}\right),$$

    

    and / or

    (c) its ultimate tensile strength in direction LT R_m(LT) expressed in MPa and its fracture toughness K_Q(L-T), in direction L-T expressed in MPa √m are such that K_Q(L-T) > 88 - 0,09 R_m(LT), and / or

    (d) its maximum stress for the initiation of fatigue cracks for a number of cycles to break of 10⁵ is greater than 210 MPa for specimens with Kt = 2.3, with R = 0.1.
11. Extruded product according to any of claims 8 to 10 of which the thickness of at least one elementary rectangle is greater than 8 mm and preferably greater than 12 mm.
12. Flat-rolled aluminum alloy product with a density lower than 2.67 g/cm³ obtained by the process according to any of claims 1 to 7 characterized in that its fracture toughness K_Q(L-T), in direction L-T is at least 23 MPa√m and its conventional limit elastic measured at 0.2% elongation in direction L R_p0,2(L) is at least equal to 560 MPa and/or its ultimate tensile strength in direction L R_m(L) is at least equal to 585 MPa.
13. Flat-rolled product according to claim 12 whose thickness is at least 10 mm and preferably at least 15 mm.
14. Structural element incorporating at least one product according to any of claims 8 to 13 or manufactured using such a product.
15. Structural element according to claim 14 including at least one extruded product according to any of claims 8 to 11 used as a stiffener or framework, characterized in that it is used for the manufacture of aircraft fuselage panels or wing skins.

Images