EP3411508B1 - Thick al - cu - li - alloy sheets having improved fatigue properties - Google Patents

Thick al - cu - li - alloy sheets having improved fatigue properties Download PDF

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EP3411508B1
EP3411508B1 EP17707940.7A EP17707940A EP3411508B1 EP 3411508 B1 EP3411508 B1 EP 3411508B1 EP 17707940 A EP17707940 A EP 17707940A EP 3411508 B1 EP3411508 B1 EP 3411508B1
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EP3411508A1 (en
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Jean-Christophe Ehrstrom
Carla DA FONSECA BARBATTI
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Constellium Issoire SAS
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    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/12—Alloys based on aluminium with copper as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/12—Alloys based on aluminium with copper as the next major constituent
    • C22C21/14—Alloys based on aluminium with copper as the next major constituent with silicon
    • 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
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/12—Alloys based on aluminium with copper as the next major constituent
    • C22C21/18—Alloys based on aluminium with copper as the next major constituent with zinc

Definitions

  • the present invention generally relates to thick sheets of Al-Cu-Li alloy and in particular to such products used in the aeronautical and aerospace industry.
  • Products, in particular thick rolled products, the thickness of which is typically at least 50 mm, made of aluminum alloy are developed to produce by cutting, surfacing or machining in the mass of high resistance parts intended in particular for the aeronautical industry. , the aerospace industry or mechanical engineering.
  • Aluminum alloys containing lithium are very interesting in this regard, 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.
  • the patent US 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, having in particular a toughness K 1C (L)> 37.4 MPa ⁇ m for a limit elasticity R p0.2 (L)> 448.2 MPa (products thicker than 76.2 mm) and in particular a toughness K 1C (L)> 38.5 MPa ⁇ m for an elastic limit R p0.2 (L)> 489.5 MPa (products less than 76.2 mm thick).
  • the AA2050 alloy includes (% 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 the alloy 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 mechanical strength and toughness, especially for thick rolled products and are selected in certain aircraft.
  • the interval between two operations of control of the structure depends on the speed and the way in which the cracks propagate in the materials used for the structure and it is advantageous to use products for which the cracks spread slowly and predictably.
  • the improvement of the propagation properties of fatigue cracks therefore relates in particular to the speed of propagation and the direction of propagation.
  • the patent application WO2009103899 thus describes an essentially non-recrystallized laminated product comprising in% by weight: 2.2 to 3.9% by weight of Cu, 0.7 to 2.1% by weight of Li; 0.2 to 0.8% by weight of Mg; 0.2 to 0.5% by weight of Mn; 0.04 to 0.18% by weight of Zr; less than 0.05% by weight of Zn and, optionally, 0.1 to 0.5% by weight of Ag, the remainder being aluminum and unavoidable impurities, having a low propensity for crack bifurcation during a fatigue test in the direction of LS.
  • Bifurcation of cracks, crack deflection, rotation of cracks or branching of cracks are terms used to express the propensity for the propagation of a crack to deviate from the expected plane of fracture perpendicular to the load applied during a stress test. tiredness or tenacity.
  • the crack bifurcation occurs on the microscopic scale ( ⁇ 100 ⁇ m), on the mesoscopic scale (100-1000 ⁇ m) or on the macroscopic scale (> 1 mm), but it is only considered harmful if the direction of the crack remains stable after bifurcation (macroscopic scale).
  • the term crack bifurcation is used here for the macroscopic bifurcation of cracks during fatigue or toughness tests in the LS direction, from the S direction to the L direction which occurs for rolled products whose thickness is at least minus 50 mm.
  • a first object of the invention is a laminated product with a thickness of at least 50 mm made of aluminum alloy comprising in% by weight 2.2 to 3.9% of Cu, 0.7 to 1.8% of Li, 0.1 to 0.8% Mg, 0.1 to 0.6% Mn; 0.01 to 0.15% of Ti, at least one element chosen from Zn and Ag, the quantity of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, optionally at least one element chosen from Zr, Cr, Sc, Hf, and V, the amount of said element if it is chosen being 0.04 to 0.18% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V, less than 0.1% of Fe, less than 0.1% of Si remains aluminum and unavoidable impurities, of a content less than 0 , 05% each and 0.15% in total; characterized in that its granular structure is mainly recrystallized between 1 ⁇ 4 and 1 ⁇ 2 thickness.
  • Yet another object of the invention is the use of a sheet according to the invention for the production of an aircraft wing spar or an aircraft wing rib.
  • the static mechanical characteristics in other words the tensile strength R m , the conventional yield strength at 0.2% elongation R p0.2 and the elongation at break A, are determined by a tensile test according to standard EN 10002-1, the sampling and the direction of the test being defined by standard EN 485-1. Unless otherwise stated, the definitions of standard EN 12258-1 apply.
  • the cracking speed (da / dN) is determined according to ASTM E 647.
  • the stress intensity factor (K 1C ) is determined according to standard ASTM E 399.
  • the present inventors have surprisingly found that laminated products with a thickness of at least 50 mm made of an aluminum - copper - lithium - magnesium - manganese alloy have advantageous properties when the granular structure is mainly recrystallized between 1 ⁇ 4 and 1 ⁇ 2 thickness.
  • the resistance to fatigue crack propagation is improved while the compromise between mechanical strength and toughness is not significantly degraded.
  • granular structure predominantly recrystallized between 1 ⁇ 4 and 1 ⁇ 2 thickness is meant a granular structure whose recrystallization rate is at least 50% between 1 ⁇ 4 and 1 ⁇ 2 thickness, that is to say of which at least 50% of the grains between 1 ⁇ 4 and 1 ⁇ 2 thickness are recrystallized.
  • the recrystallization rate between 1 ⁇ 4 and 1 ⁇ 2 thickness is at least 55%.
  • the thickness of the products according to the invention is between 80 and 130 mm.
  • the products according to the invention have a copper content of between 2.2 and 3.9% by weight.
  • the copper content is at least 2.8% by weight and preferably at least 3.2% by weight.
  • the maximum copper content is 3.8% by weight.
  • the products according to the invention have a lithium content of between 0.7 and 1.8% by weight.
  • the lithium content is at least 0.8% by weight and preferably at least 0.9% by weight.
  • the maximum lithium content is 1.5% by weight, preferably 1.1% and preferably 0.95% by weight.
  • the products according to the invention have a magnesium content of between 0.1 and 0.8% by weight.
  • the magnesium content is at least 0.2% by weight and preferably at least 0.3% by weight.
  • the maximum magnesium content is 0.7% by weight and preferably 0.6% by weight.
  • the products according to the invention have a manganese content of between 0.1 and 0.6% by weight.
  • the manganese content is at least 0.2% by weight and preferably at least 0.3% by weight.
  • the maximum manganese content is 0.5% by weight and preferably 0.4% by weight.
  • the products according to the invention contain at least one element chosen from Zn and Ag, the amount of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, these elements being particularly useful for hardening of the alloy. Preferably, only one of these elements is added, the second being maintained at a content of less than 0.05% by weight.
  • the products according to the invention contain at least one element chosen from Zr, Cr, Sc, Hf, and V, the amount of said element if it is chosen being 0.04 to 0.18% and preferably 0.04 to 0.15% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V.
  • These elements contribute to the control of the granular structure.
  • the granular structure mainly recrystallized according to the invention is obtained by means of a selection of the processing parameters, in particular the conditions for homogenization and hot rolling.
  • the sum of the content of the elements Zr, Cr, Sc, Hf, and V is preferably at least 0.08% by weight.
  • the Zr content in this first embodiment is from 0.08 to 0.10% by weight.
  • the mainly recrystallized granular structure according to the invention is obtained by limiting the content of elements acting on the control of the granular structure.
  • the sum of the content of the elements Zr, Cr, Sc, Hf, and V is less than 0.08% by weight.
  • the Zr content is from 0.04 to 0.07% by weight and preferably 0.05 to 0.07% by weight.
  • there is no addition of Zr the Zr content is less than 0.05% by weight, preferably less than 0.04% by weight and more preferably still less at 0.02% by weight. It is also possible in certain cases to combine these two embodiments.
  • the products according to the invention also have advantageous properties in terms of propensity to crack bifurcation.
  • the macroscopic bifurcation of cracks during fatigue tests in the LS direction, from the S direction to the L direction was evaluated in two ways.
  • the figure 5c shows an example of evaluation of this distance: when the crack deviates, it does not immediately join the direction L and one can thus measure the distance d.
  • One considers that the crack is in direction S or direction L when it does not deviate from this direction by more than 10 °.
  • the process for manufacturing a mainly recrystallized granular sheet with a thickness of at least 50 mm comprises the steps of casting, homogenization, hot rolling, dissolution, quenching, controlled traction and tempering.
  • An alloy containing controlled quantities according to the invention of alloying elements is cast in the form of a plate.
  • the plate is homogenized at a temperature of at least 490 ° C.
  • Preferably the homogenization time is at least 12 hours. Homogenization can be carried out in one or more stages.
  • the homogenization comprises at least one step whose temperature is at least 520 ° C and preferably at least 530 ° C, the period during which the temperature is above 520 ° C being at least 20 hours and preferably at least 30 hours.
  • a hot rolling step is carried out after reheating if necessary to obtain sheets whose thickness is at least 50 mm.
  • the hot rolling outlet temperature is less than 390 ° C, preferably less than 380 ° C.
  • the combination in particular of the conditions of the homogenization step and of the hot rolling step of the first embodiment makes it possible to obtain a final structure after mostly recrystallized tempering, in particular for products whose sum of the content of the elements Zr , Cr, Sc, Hf, and V is at least 0.08% by weight.
  • the inventors have found that the conditions according to this first embodiment make it possible to reduce the propensity for crack bifurcation.
  • the sum of the content of the elements Zr, Cr, Sc, Hf, and V is less than 0.08% by weight and the outlet temperature from hot rolling is preferably at least 400 ° C and preferably at least 420 ° C.
  • the sheets are dissolved by heating between 490 and 540 ° C, preferably for 15 minutes to 4 hours, the dissolution parameters depending on the thickness of the product.
  • Cold water quenching is carried out after dissolution.
  • the product then undergoes controlled traction with a permanent deformation of between 1% and 7% and preferably between 2% and 6%.
  • Tempering is carried out at a temperature between 130 ° C and 170 ° C and preferably at a temperature between 140 ° C and 160 ° C for a period of 5 to 60 hours, which results in a T8 state. In certain cases, and in particular for certain preferred compositions, the tempering is carried out preferably between 140 and 160 ° C. for 12 to 50 hours.
  • the products according to the invention are advantageously used in aeronautical construction.
  • the use of the products according to the invention for producing an aircraft wing spar or an aircraft wing rib is particularly advantageous.
  • the use of the products according to the invention for the production of an aircraft wing spar is preferred, advantageously for the lower part, that is to say in connection with the lower surface of the wing, d '' a welded beam.
  • Plate A was homogenized in two stages of 36 hours at 504 ° C and then 48 hours at 530 ° C. Plates B and C were homogenized in two steps of 8 hours at 496 ° C and then 34 hours at 530 ° C. Plate D was homogenized for 12 hours at 505 ° C. Plate E was homogenized in two stages 8 h at 500 ° C and then 36 hours at 527 ° C.
  • Plate A was hot rolled to a 100 mm thick sheet, the hot rolling inlet temperature was 410 ° C and the hot rolling outlet temperature was 361 ° C.
  • Plate B was hot rolled to a 102 mm thick sheet, the hot rolling inlet temperature was 406 ° C and the hot rolling outlet temperature was 350 ° C.
  • Plate C was hot rolled to a 102 mm thick sheet, the hot rolling inlet temperature was 410 ° C and the hot rolling outlet temperature was 360 ° C.
  • Plate D was hot rolled to a 100 mm thick sheet, the hot rolling inlet temperature was 505 ° C and the hot rolling outlet temperature was 520 ° C.
  • Plate E was hot rolled to a 100 mm thick sheet, the hot rolling inlet temperature was 481 ° C and the hot rolling outlet temperature was 460 ° C.
  • the sheets thus obtained were dissolved for 2 hours at 525 ° C and quenched with cold water.
  • the sheets thus dissolved and quenched were pulled in a controlled manner, with a permanent elongation of 4% and underwent an 18 hour tempering at 155 ° C (A, B, C and E) or 24 h at 155 ° C (D).
  • Fatigue crack propagation tests on L-S test pieces were carried out on samples from sheets C and E. The tests were carried out according to standard ASTM E647. These tests are carried out on CCT specimens, with central crack, of width 100 mm and thickness 6.35 mm.
  • the marks 84A2 and A2, B2 and C2 were tested at 3000 N of maximum force rather than 4000 N.
  • the conditions make it possible during the test to cover the range of ⁇ K ranging from 10 at 40 MPa ⁇ m, where ⁇ K is the variation of the stress intensity factor in a charge cycle.
  • the figures 3a and 3b show, respectively, the samples from sheets A and D after the fatigue test.
  • the samples from sheet A according to the invention exhibit a progressive crack bifurcation with in 4 out of 6 cases (C1, C2, B1, A2) a rupture by the rear face of the test piece.
  • the distance d over which the crack is neither in the initial S direction, nor in the L direction is at least 15 mm for all samples from sheet A, because in none of the cases does the crack join the direction L.
  • the figure 4 shows the propagation speed results measured by the crack opening method, during tests on CT specimens. These tests also show that the propagation speed is significantly slower, in the LS direction, for sheet A according to the invention.
  • the mainly recrystallized product according to the invention has a particularly advantageous propagation of fatigue cracks.
  • Samples of format 14 mm x 50 mm x 56 mm were machined at half-width (L / 2) and quarter-thickness (T / 4) of the casting plates.
  • the figure 6 presents such samples of thickness C 14 mm and width B 50 mm.
  • the samples were homogenized in two stages of 5 hours at 505 ° C and then 12 hours at 525 ° C.
  • the samples were hot deformed by double punching using a "Servotest" ® type machine, the temperature and the speed of deformation were 400 ° C and 1s -1 respectively .
  • the figure 6 illustrates such a deformation by double-punching.
  • Such a deformation is representative of an industrial deformation by hot rolling of a foundry plate of approximately 400 mm to a final thickness of approximately 100 mm.
  • the samples F and G are mainly recrystallized.

Description

Domaine de l'inventionField of the invention

La présente invention concerne en général les tôles épaisses en alliage Al-Cu-Li et en particulier de tels produits utilisés dans l'industrie aéronautique et aérospatiale.The present invention generally relates to thick sheets of Al-Cu-Li alloy and in particular to such products used in the aeronautical and aerospace industry.

Etat de la techniqueState of the art

Des produits, notamment des produits laminés épais, dont l'épaisseur est typiquement au moins 50 mm, en alliage d'aluminium sont développés pour produire par découpage, surfaçage ou usinage dans la masse des pièces de haute résistance destinées notamment à l'industrie aéronautique, à l'industrie aérospatiale ou à la construction mécanique.
Les alliages d'aluminium contenant du lithium sont très intéressants à cet égard, car le lithium peut réduire la densité de l'aluminium de 3 % et augmenter le module d'élasticité de 6 % pour chaque pourcent en poids de lithium ajouté. Pour que ces alliages soient sélectionnés dans les avions, leur performance par rapport aux autres propriétés d'usage doit atteindre celle des alliages couramment utilisés, en particulier en terme de compromis entre les propriétés de résistance mécanique statique (limite d'élasticité, résistance à la rupture) et les propriétés de tolérance aux dommages (ténacité, résistance à l'initiation et à la propagation des fissures en fatigue), ces propriétés étant en général antinomiques. Pour les produits épais, ces propriétés doivent en particulier être obtenues à quart et à mi-épaisseur. Ces produits doivent également présenter une résistance à la corrosion suffisante, pouvoir être mis en forme selon les procédés habituels et présenter de faibles contraintes résiduelles de façon à pouvoir être usinés de façon intégrale.Products, in particular thick rolled products, the thickness of which is typically at least 50 mm, made of aluminum alloy are developed to produce by cutting, surfacing or machining in the mass of high resistance parts intended in particular for the aeronautical industry. , the aerospace industry or mechanical engineering.
Aluminum alloys containing lithium are very interesting in this regard, 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. In order for these alloys to be selected in airplanes, their performance in relation to the other properties of use must reach that of the commonly used alloys, in particular in terms of compromise between the properties of static mechanical resistance (elastic limit, resistance to rupture) and the damage tolerance properties (toughness, resistance to initiation and propagation of cracks in fatigue), these properties being in general contradictory. For thick products, these properties must in particular be obtained at quarter and half thickness. These products 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 fully machined.

Le brevet US 5,032,359 décrit une vaste famille d'alliages aluminium-cuivre-lithium dans lesquels l'addition de magnésium et d'argent, en particulier entre 0,3 et 0,5 pourcent en poids, permet d'augmenter la résistance mécanique.The patent US 5,032,359 describes 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 resistance.

Le brevet US 7,229,509 décrit un alliage comprenant (% en poids) : (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 ou d'autres agents affinant le grain tels que Cr, Ti, Hf, Sc, V, présentant notamment une ténacité K1C(L)>37,4 MPa√m pour une limite d'élasticité Rp0,2(L) > 448,2 MPa (produits d'épaisseur supérieure à 76,2 mm) et notamment une ténacité K1C(L)>38,5 MPa√m pour une limite d'élasticité Rp0,2(L) > 489,5 MPa (produits d'épaisseur inférieure à 76,2 mm).The patent US 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, having in particular a toughness K 1C (L)> 37.4 MPa√m for a limit elasticity R p0.2 (L)> 448.2 MPa (products thicker than 76.2 mm) and in particular a toughness K 1C (L)> 38.5 MPa√m for an elastic limit R p0.2 (L)> 489.5 MPa (products less than 76.2 mm thick).

L'alliage AA2050 comprend (% en poids) : (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 et l'alliage 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. Les produits en alliage AA2050 sont connus pour leur qualité en termes de résistance mécanique statique et de ténacité, notamment pour des produits laminés épais et sont sélectionnés dans certains avions.The AA2050 alloy includes (% 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 the alloy 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 mechanical strength and toughness, especially for thick rolled products and are selected in certain aircraft.

Pour certaines applications il peut être avantageux d'améliorer encore les propriétés de ces produits notamment en ce qui concerne la propagation des fissures en fatigue.
En effet, pour un avion l'intervalle entre deux opérations de contrôle de la structure dépend de la vitesse et de la façon dont les fissures se propagent dans les matériaux utilisés pour la structure et il est avantageux d'utiliser des produits pour lesquels les fissures se propagent lentement et de manière prévisible. L'amélioration des propriétés de propagation des fissures en fatigue concerne donc notamment la vitesse de propagation et la direction de propagation.For certain applications it may be advantageous to further improve the properties of these products, in particular as regards the propagation of fatigue cracks.
Indeed, for an airplane the interval between two operations of control of the structure depends on the speed and the way in which the cracks propagate in the materials used for the structure and it is advantageous to use products for which the cracks spread slowly and predictably. The improvement of the propagation properties of fatigue cracks therefore relates in particular to the speed of propagation and the direction of propagation.

La demande de brevet WO2009103899 décrit ainsi un produit laminé essentiellement non recristallisé comprenant en % en poids: 2,2 à 3,9% en poids de Cu, 0,7 à 2,1% en poids de Li; 0,2 à 0,8% en poids de Mg; 0,2 à 0,5% en poids de Mn; 0,04 à 0,18% en poids de Zr; moins de 0,05% en poids de Zn et, facultativement, 0,1 à 0,5% en poids de Ag, le reste étant de l'aluminium et des impuretés inévitables, ayant une faible propension à la bifurcation fissure lors d'un test de fatigue dans la direction de LS.
La bifurcation des fissures, la déviation de fissure, la rotation des fissures ou le branchement des fissures sont des termes utilisés pour exprimer la propension pour la propagation d'une fissure de dévier du plan attendu de fracture perpendiculaire à la charge appliquée pendant un test de fatigue ou de ténacité. La bifurcation de fissure se produit à l'échelle microscopique (<100 µm), à l'échelle mésoscopique (100-1000 µm) ou à l'échelle macroscopique (> 1 mm), mais elle n'est considérée comme néfaste que si la direction de la fissure reste stable après bifurcation (échelle macroscopique). Le terme bifurcation de fissure est utilisé ici pour la bifurcation macroscopique de fissures lors de tests en fatigue ou en ténacité dans la direction L-S, de la direction S vers la direction L qui se produit pour des produits laminés dont l'épaisseur est d'au moins 50 mm.The patent application WO2009103899 thus describes an essentially non-recrystallized laminated product comprising in% by weight: 2.2 to 3.9% by weight of Cu, 0.7 to 2.1% by weight of Li; 0.2 to 0.8% by weight of Mg; 0.2 to 0.5% by weight of Mn; 0.04 to 0.18% by weight of Zr; less than 0.05% by weight of Zn and, optionally, 0.1 to 0.5% by weight of Ag, the remainder being aluminum and unavoidable impurities, having a low propensity for crack bifurcation during a fatigue test in the direction of LS.
Bifurcation of cracks, crack deflection, rotation of cracks or branching of cracks are terms used to express the propensity for the propagation of a crack to deviate from the expected plane of fracture perpendicular to the load applied during a stress test. tiredness or tenacity. The crack bifurcation occurs on the microscopic scale (<100 µm), on the mesoscopic scale (100-1000 µm) or on the macroscopic scale (> 1 mm), but it is only considered harmful if the direction of the crack remains stable after bifurcation (macroscopic scale). The term crack bifurcation is used here for the macroscopic bifurcation of cracks during fatigue or toughness tests in the LS direction, from the S direction to the L direction which occurs for rolled products whose thickness is at least minus 50 mm.

Il existe un besoin pour un produit laminé en alliage aluminium lithium pour des applications aéronautiques, en particulier pour des pièces intégralement usinées, ayant des propriétés de propagation de fissures en fatigue améliorées et ayant une faible propension à la bifurcation de fissure.There is a need for a laminated aluminum alloy product for aeronautical applications, in particular for fully machined parts, having improved fatigue crack propagation properties and having a low propensity for crack bifurcation.

Objet de l'inventionSubject of the invention

Un premier objet de l'invention est un produit laminé d'épaisseur au moins 50 mm en alliage d'aluminium comprenant en % en poids 2,2 à 3,9 % de Cu, 0,7 à 1,8 % de Li, 0,1 à 0,8 % de Mg, 0,1 à 0,6 % de Mn ; 0,01 à 0,15 % de Ti, au moins un élément choisi parmi Zn et Ag, la quantité dudit élément s'il est choisi étant 0,2 à 0,8 % pour Zn et 0,1 à 0,5 % pour Ag, optionnellement au moins un élément choisi parmi Zr, Cr, Sc, Hf, et V, la quantité dudit élément s'il est choisi étant 0,04 à 0,18 % pour Zr, 0,05 à 0,3 % pour Cr et pour Sc, 0,05 à 0,5 % pour Hf et pour V, moins de 0,1 % de Fe, moins de 0,1 % de Si reste aluminium et impuretés inévitables, d'une teneur inférieure à 0,05 % chacune et 0,15% au total ; caractérisé en ce que sa structure granulaire est majoritairement recristallisée entre le ¼ et la ½ épaisseur.A first object of the invention is a laminated product with a thickness of at least 50 mm made of aluminum alloy comprising in% by weight 2.2 to 3.9% of Cu, 0.7 to 1.8% of Li, 0.1 to 0.8% Mg, 0.1 to 0.6% Mn; 0.01 to 0.15% of Ti, at least one element chosen from Zn and Ag, the quantity of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, optionally at least one element chosen from Zr, Cr, Sc, Hf, and V, the amount of said element if it is chosen being 0.04 to 0.18% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V, less than 0.1% of Fe, less than 0.1% of Si remains aluminum and unavoidable impurities, of a content less than 0 , 05% each and 0.15% in total; characterized in that its granular structure is mainly recrystallized between ¼ and ½ thickness.

Un second objet de l'invention est un procédé de fabrication d'une tôle selon l'invention, comprenant :

  1. a) la coulée d'une plaque, en alliage d'aluminium comprenant en % en poids 2,2 à 3,9 % de Cu, 0,7 à 1,8 % de Li, 0,1 à 0,8 % de Mg, 0,1 à 0,6 % de Mn ; 0,01 à 0,15 % de Ti, au moins un élément choisi parmi Zn et Ag, la quantité dudit élément s'il est choisi étant 0,2 à 0,8 % pour Zn et 0,1 à 0,5 % pour Ag, optionnellement au moins un élément choisi parmi Zr, Cr, Sc, Hf, et V, la quantité dudit élément s'il est choisi étant 0,04 à 0,18 % pour Zr, 0,05 à 0,3 % pour Cr et pour Sc, 0,05 à 0,5 % pour Hf et pour V, moins de 0,1 % de Fe, moins de 0,1 % de Si reste aluminium et impuretés inévitables, d'une teneur inférieure à 0,05 % en poids chacune et 0,15% au total;
  2. b) l'homogénéisation de ladite plaque à une température d'au moins 490 °C,
  3. c) le laminage à chaud de ladite plaque pour obtenir une tôle d'au moins 50 mm d'épaisseur,
  4. d) la mise en solution entre 490 °C et 540 °C,
  5. e) la trempe à l'eau froide,
  6. f) la traction contrôlée de la dite tôle avec une déformation permanente de 1 à 7 %,
  7. g) le revenu de ladite tôle par chauffage entre 130°C et 160 °C pendant 5 à 60 heures, caractérisé en ce que la somme de la teneur des éléments Zr, Cr, Sc, Hf, et V est inférieure à 0,08 % en poids et/ou en ce que lors de l'étape b) la température d'homogénisation est d'au moins 520 °C pour une durée d'au moins 20 heures et lors de l'étape c) la température de sortie du laminage à chaud est inférieure à 390 °C.
A second object of the invention is a method of manufacturing a sheet according to the invention, comprising:
  1. a) the casting of a plate, of aluminum alloy comprising in% by weight 2.2 to 3.9% of Cu, 0.7 to 1.8% of Li, 0.1 to 0.8% of Mg, 0.1 to 0.6% Mn; 0.01 to 0.15% of Ti, at least one element chosen from Zn and Ag, the quantity of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, optionally at least one element chosen from Zr, Cr, Sc, Hf, and V, the amount of said element if it is chosen being 0.04 to 0.18% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V, less than 0.1% of Fe, less than 0.1% of Si remains aluminum and unavoidable impurities, of a content less than 0 0.05% by weight each and 0.15% in total;
  2. b) the homogenization of said plate at a temperature of at least 490 ° C,
  3. c) hot rolling said plate to obtain a sheet at least 50 mm thick,
  4. d) dissolving between 490 ° C and 540 ° C,
  5. e) quenching with cold water,
  6. f) the controlled traction of said sheet with a permanent deformation of 1 to 7%,
  7. g) the income of said sheet by heating between 130 ° C and 160 ° C for 5 to 60 hours, characterized in that the sum of the content of the elements Zr, Cr, Sc, Hf, and V is less than 0.08 % by weight and / or in that during step b) the homogenization temperature is at least 520 ° C for a period of at least 20 hours and during step c) the outlet temperature hot rolling is less than 390 ° C.

Encore un autre objet de l'invention est l'utilisation d'une tôle selon l'invention pour la réalisation d'un longeron d'aile d'avion ou d'une nervure d'aile d'avion.Yet another object of the invention is the use of a sheet according to the invention for the production of an aircraft wing spar or an aircraft wing rib.

Description des figuresDescription of the figures

  • Figure 1 : Schéma de l'éprouvette CT utilisée pour les essais de propagation de fissure en fatigue. Les dimensions sont indiquées en mm. Figure 1 : Diagram of the CT specimen used for fatigue crack propagation tests. Dimensions are given in mm.
  • Figure 2. Vitesses de propagation de fissure obtenues sur éprouvettes CCT pour la tôle de référence E et la tôle C selon l'invention. Figure 2 . Crack propagation speeds obtained on CCT test pieces for the reference sheet E and the sheet C according to the invention.
  • Figure 3a - Tôle A, selon l'invention, après test de fatigue sur éprouvette CT pour 6 éprouvettes. Figure 3a - Sheet A, according to the invention, after fatigue test on a CT test piece for 6 test pieces.
  • Figure 3b - Tôle D de référence, après test de fatigue sur éprouvette CT pour 6 éprouvettes. Figure 3b - Reference sheet D, after fatigue test on a CT test piece for 6 test pieces.
  • Figure 4 - Vitesses de propagations de fissures obtenues avec l'éprouvette CT. Figure 4 - Crack propagation velocities obtained with the CT specimen.
  • Figure 5 : Différents modes de propagation de fissure sur l'éprouvette CT selon la Figure 1, ayant une face arrière (1), une face inférieure (22) et une face supérieure (21). Les directions S et L sont indiquées. Figure 5a : faible propension à la bifurcation de fissure et rupture par la face arrière (1), 5b : forte propension à la bifurcation de fissure et rupture par la face inférieure (22), 5c : faible propension à la bifurcation de fissure, rupture par la face supérieure (21) mais distance d sur laquelle la fissure n'est ni dans la direction S initiale, ni dans la direction L d'au moins 5 mm. Figure 5 : Different modes of crack propagation on the CT specimen according to the Figure 1 , having a rear face (1), a lower face (22) and an upper face (21). The directions S and L are indicated. Figure 5a : low propensity for crack bifurcation and rupture by the rear face (1), 5b: high propensity for crack bifurcation and rupture by the underside (22), 5c: low propensity for crack bifurcation, rupture by the upper face (21) but distance d over which the crack is neither in the initial S direction nor in the L direction of at least 5 mm.
Description détaillée de l'inventionDetailed description of the invention

Sauf mention contraire, toutes les indications concernant la composition chimique des alliages sont exprimées comme un pourcentage en poids basé sur le poids total de l'alliage. L'expression 1,4 Cu signifie que la teneur en cuivre exprimée en % en poids est multipliée par 1,4. La désignation des alliages se fait en conformité avec les règlements de The Aluminium Association, connus de l'homme du métier. Les définitions des états métallurgiques sont indiquées dans la norme européenne EN 515.Unless otherwise stated, all indications concerning the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy. The expression 1.4 Cu means that the copper content expressed in% by weight is multiplied by 1.4. The designation of the alloys is done in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The definitions of metallurgical states are given in European standard EN 515.

Sauf mention contraire, les caractéristiques mécaniques statiques, en d'autres termes la résistance à la rupture Rm, la limite d'élasticité conventionnelle à 0,2% d'allongement Rp0,2 et l'allongement à la rupture A, sont déterminées par un essai de traction selon la norme EN 10002-1, le prélèvement et le sens de l'essai étant définis par la norme EN 485-1. Sauf mention contraire, les définitions de la norme EN 12258-1 s'appliquent.
La vitesse de fissuration (da/dN) est déterminée selon la norme ASTM E 647.
Le facteur d'intensité de contrainte (K1C) est déterminé selon la norme ASTM E 399.Unless otherwise stated, the static mechanical characteristics, in other words the tensile strength R m , the conventional yield strength at 0.2% elongation R p0.2 and the elongation at break A, are determined by a tensile test according to standard EN 10002-1, the sampling and the direction of the test being defined by standard EN 485-1. Unless otherwise stated, the definitions of standard EN 12258-1 apply.
The cracking speed (da / dN) is determined according to ASTM E 647.
The stress intensity factor (K 1C ) is determined according to standard ASTM E 399.

Pour les produits épais en alliage d'aluminium, l'homme du métier recherche une structure granulaire non recristallisée car celle-ci est notamment connue pour être favorable à la ténacité et à la résistance à la propagation de fissure en fatigue (voir par exemple, l'article de référence « Application of Modem Aluminum Alloys to Aircraft », Prog. Aerospace Sci. Vol 32 pp 131-172, 1996, E.A Starke and J.T Staley, p156 , et R.J.H. Wanhill and G.H. Bray, « Fatigue Crack Growth Behavior of Aluminum-Lithium Alloys », in Aluminium-Lithium alloys Processing, Properties and Applications, Chapitre 12 pages 381-413, Elsevier 2014, p386 ).
Les présents inventeurs ont constaté de manière surprenante, que des produits laminés d'épaisseur au moins 50 mm en alliage Aluminium - Cuivre - Lithium - Magnésium - Manganèse présentent des propriétés avantageuses lorsque la structure granulaire est majoritairement recristallisée entre le ¼ et la ½ épaisseur. Ainsi, de manière surprenante, pour les produits épais selon l'invention, la résistance à la propagation de fissure en fatigue est améliorée alors que le compromis entre résistance mécanique et ténacité n'est pas dégradé de manière significative. Par structure granulaire majoritairement recristallisée entre le ¼ et la ½ épaisseur, on entend une structure granulaire dont le taux de recristallisation est au moins 50 % entre le ¼ et la ½ épaisseur c'est-à-dire dont au moins 50 % des grains entre le ¼ et la ½ épaisseur sont recristallisés. De préférence le taux de recristallisation entre ¼ et la ½ épaisseur est au moins 55%. Avantageusement l'épaisseur des produits selon l'invention est comprise entre 80 et 130 mm.
Les produits selon l'invention ont une teneur en cuivre comprise entre 2,2 et 3,9 % en poids. De préférence la teneur en cuivre est au moins 2,8 % en poids et préférentiellement au moins 3,2 % en poids. Avantageusement la teneur maximale en cuivre est 3,8 % en poids.
Les produits selon l'invention ont une teneur en lithium comprise entre 0,7 et 1,8 % en poids. De préférence la teneur en lithium est au moins 0,8 % en poids et préférentiellement au moins 0,9 % en poids. Avantageusement la teneur maximale en lithium est 1,5 % en poids, préférentiellement 1,1 % et de manière préférée 0,95 % en poids.For thick aluminum alloy products, a person skilled in the art searches for a non-recrystallized granular structure because it is notably known to be favorable to toughness and to resistance to crack propagation in fatigue (see for example, reference article "Application of Modem Aluminum Alloys to Aircraft", Prog. Aerospace Sci. Vol 32 pp 131-172, 1996, EA Starke and JT Staley, p156 , and RJH Wanhill and GH Bray, "Fatigue Crack Growth Behavior of Aluminum-Lithium Alloys", in Aluminum-Lithium alloys Processing, Properties and Applications, Chapter 12 pages 381-413, Elsevier 2014, p386 ).
The present inventors have surprisingly found that laminated products with a thickness of at least 50 mm made of an aluminum - copper - lithium - magnesium - manganese alloy have advantageous properties when the granular structure is mainly recrystallized between ¼ and ½ thickness. Thus, surprisingly, for thick products according to the invention, the resistance to fatigue crack propagation is improved while the compromise between mechanical strength and toughness is not significantly degraded. By granular structure predominantly recrystallized between ¼ and ½ thickness, is meant a granular structure whose recrystallization rate is at least 50% between ¼ and ½ thickness, that is to say of which at least 50% of the grains between ¼ and ½ thickness are recrystallized. Preferably the recrystallization rate between ¼ and ½ thickness is at least 55%. Advantageously, the thickness of the products according to the invention is between 80 and 130 mm.
The products according to the invention have a copper content of between 2.2 and 3.9% by weight. Preferably the copper content is at least 2.8% by weight and preferably at least 3.2% by weight. Advantageously, the maximum copper content is 3.8% by weight.
The products according to the invention have a lithium content of between 0.7 and 1.8% by weight. Preferably the lithium content is at least 0.8% by weight and preferably at least 0.9% by weight. Advantageously, the maximum lithium content is 1.5% by weight, preferably 1.1% and preferably 0.95% by weight.

Les produits selon l'invention ont une teneur en magnésium comprise entre 0,1 et 0,8 % en poids. De préférence la teneur en magnésium est au moins 0,2 % en poids et préférentiellement au moins 0,3 % en poids. Avantageusement la teneur maximale en magnésium est 0,7 % en poids et de manière préférée 0,6 % en poids.
Les produits selon l'invention ont une teneur en manganèse comprise entre 0,1 et 0,6 % en poids. De préférence la teneur en manganèse est au moins 0,2 % en poids et préférentiellement au moins 0,3 % en poids. Avantageusement la teneur maximale en manganèse est 0,5 % en poids et de manière préférée 0,4 % en poids.
Les produits selon l'invention contiennent au moins un élément choisi parmi Zn et Ag, la quantité dudit élément s'il est choisi étant 0,2 à 0,8 % pour Zn et 0,1 à 0,5 % pour Ag, ces éléments étant notamment utiles au durcissement de l'alliage. De manière préférée, on ajoute un seul de ces éléments, le second étant maintenu à une teneur inférieure à 0,05 % en poids.The products according to the invention have a magnesium content of between 0.1 and 0.8% by weight. Preferably the magnesium content is at least 0.2% by weight and preferably at least 0.3% by weight. Advantageously, the maximum magnesium content is 0.7% by weight and preferably 0.6% by weight.
The products according to the invention have a manganese content of between 0.1 and 0.6% by weight. Preferably the manganese content is at least 0.2% by weight and preferably at least 0.3% by weight. Advantageously, the maximum manganese content is 0.5% by weight and preferably 0.4% by weight.
The products according to the invention contain at least one element chosen from Zn and Ag, the amount of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, these elements being particularly useful for hardening of the alloy. Preferably, only one of these elements is added, the second being maintained at a content of less than 0.05% by weight.

Optionnellement les produits selon l'invention contiennent au moins un élément choisi parmi Zr, Cr, Sc, Hf, et V, la quantité dudit élément s'il est choisi étant 0,04 à 0,18 % et de préférence 0,04 à 0,15 % pour Zr, 0,05 à 0,3 % pour Cr et pour Sc, 0,05 à 0,5 % pour Hf et pour V. Ces éléments contribuent au contrôle de la structure de granulaire.
Il existe principalement deux modes de réalisation de l'invention.
Dans un premier mode de réalisation de l'invention, la structure granulaire majoritairement recristallisée selon l'invention est obtenue grâce à une sélection des paramètres de transformation, notamment les conditions d'homogénéisation et de laminage à chaud. Dans ce premier mode de réalisation, la somme de la teneur des éléments Zr, Cr, Sc, Hf, et V est de préférence au moins 0,08 % en poids. De manière préférée, la teneur en Zr dans ce premier mode de réalisation est de 0,08 à 0,10 % en poids.
Dans un second mode de réalisation, la structure granulaire majoritairement recristallisée selon l'invention est obtenue en limitant la teneur en éléments agissant sur le contrôle de la structure granulaire. Dans ce second mode de réalisation, la somme de la teneur des éléments Zr, Cr, Sc, Hf, et V est inférieure à 0,08 % en poids. Dans une réalisation particulière de ce second mode, la teneur en Zr est de 0,04 à 0,07 % en poids et de préférence 0,05 à 0,07 % en poids. Dans une autre réalisation particulière de ce second mode, il n'y a pas d'ajout de Zr, la teneur en Zr est inférieure à 0,05 % en poids, préférentiellement inférieure à 0,04% en poids et plus préférentiellement encore inférieure à 0,02 % en poids.
On peut également dans certains cas combiner ces deux modes de réalisation.Optionally, the products according to the invention contain at least one element chosen from Zr, Cr, Sc, Hf, and V, the amount of said element if it is chosen being 0.04 to 0.18% and preferably 0.04 to 0.15% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V. These elements contribute to the control of the granular structure.
There are mainly two embodiments of the invention.
In a first embodiment of the invention, the granular structure mainly recrystallized according to the invention is obtained by means of a selection of the processing parameters, in particular the conditions for homogenization and hot rolling. In this first embodiment, the sum of the content of the elements Zr, Cr, Sc, Hf, and V is preferably at least 0.08% by weight. Preferably, the Zr content in this first embodiment is from 0.08 to 0.10% by weight.
In a second embodiment, the mainly recrystallized granular structure according to the invention is obtained by limiting the content of elements acting on the control of the granular structure. In this second embodiment, the sum of the content of the elements Zr, Cr, Sc, Hf, and V is less than 0.08% by weight. In a particular embodiment of this second mode, the Zr content is from 0.04 to 0.07% by weight and preferably 0.05 to 0.07% by weight. In another particular embodiment of this second mode, there is no addition of Zr, the Zr content is less than 0.05% by weight, preferably less than 0.04% by weight and more preferably still less at 0.02% by weight.
It is also possible in certain cases to combine these two embodiments.

Les produits selon l'invention contiennent de 0,01 à 0,15 % en poids de titane, cet élément étant notamment utile pour le contrôle de la structure granulaire lors de la coulée. Préférentiellement, la teneur en titane est comprise entre 0,01 et 0,05 % en poids. La teneur des impuretés fer et silicium doit être limitée pour éviter une dégradation des propriétés de fatigue et de ténacité. Selon l'invention les produits selon l'invention contiennent moins de 0,1 % de Fe et moins de 0,1 % de Si. Préférentiellement la teneur en fer est inférieure à 0,08 % en poids et de préférence inférieure à 0,06% en poids. Préférentiellement la teneur en silicium est inférieure à 0,07 % en poids et de préférence inférieure à 0,05% en poids. Les autres éléments présents sont des impuretés inévitables dont la teneur est inférieure à 0,05 % en poids chacune et 0,15 % en poids au total. Un élément non choisi parmi Cr, Sc, Hf, V, Ag et Zn a ainsi une teneur inférieure à 0,05 % en poids et de préférence inférieure à 0,03 % en poids. Si le Zr n'est pas choisi, sa teneur est inférieure à 0,04 % en poids et de préférence inférieure à 0,02 % en poids.
Les produits selon l'invention présentent des propriétés satisfaisantes en termes de compromis entre résistance mécanique et ténacité et des propriétés très avantageuses en termes de vitesse de propagation de fissure en fatigue et en termes de sensibilité à la déviation de fissure. Ainsi, avantageusement les produits selon l'invention présentent,

  1. (i) pour une épaisseur comprise entre 50 et 75 mm, à quart-épaisseur, une limite d'élasticité Rp0,2(TL) ≥ 435 MPa et de préférence Rp0,2(TL) ≥ 455 MPa et une ténacité K1C (T-L) ≥ 28 MPa√m et avantageusement telle que K1C (T-L) ≥ 30 MPa√m,
  2. (ii) pour une épaisseur comprise entre 76 et 102 mm, à quart-épaisseur, une limite d'élasticité Rp0,2(TL) ≥ 435 MPa et de préférence Rp0,2(TL) ≥ 455 MPa et une ténacité K1C (T-L) ≥ 25 MPa√m et avantageusement telle que K1C (T-L) ≥ 27 MPa√m.
  3. (iii) pour une épaisseur comprise entre 103 et 130 mm, à quart-épaisseur, une limite d'élasticité Rp0,2(TL) ≥ 428 MPa et de préférence Rp0,2(TL) ≥ 448 MPa et une ténacité K1C (T-L) ≥ 23 MPa√m et avantageusement telle que K1C (T-L) ≥ 25 MPa√m.
  4. (iv) pour une épaisseur supérieure à 130 mm, à quart-épaisseur, une limite d'élasticité Rp0,2(TL) ≥ 428 MPa et de préférence Rp0,2(TL) ≥ 448 MPa et une ténacité K1C (T-L) ≥ 21 MPa√m et avantageusement telle que K1C (T-L) ≥ 23 MPa√m,
et ils présentent une vitesse de propagation de fissure mesurée selon la norme ASTM E647 sur éprouvettes CCT, à fissure centrale, de largeur 100 mm et d'épaisseur 6.35 mm prélevée à mi-épaisseur dans l'orientation L-S inférieure à 10-4 mm/cycle pour un ΔK = 20 MPa√m et préférentiellement inférieure à 9.10-5 mm/cycle pour un ΔK = 20 MPa√m.The products according to the invention contain from 0.01 to 0.15% by weight of titanium, this element being in particular useful for controlling the granular structure during casting. Preferably, the titanium content is between 0.01 and 0.05% by weight. The content of iron and silicon impurities must be limited to avoid degradation of the fatigue and toughness properties. According to the invention, the products according to the invention contain less than 0.1% of Fe and less than 0.1% of Si. Preferably the iron content is less than 0.08% by weight and preferably less than 0, 06% by weight. Preferably, the silicon content is less than 0.07% by weight and preferably less than 0.05% by weight. The other elements present are inevitable impurities whose content is less than 0.05% by weight each and 0.15% by weight in total. An element not chosen from Cr, Sc, Hf, V, Ag and Zn thus has a content of less than 0.05% by weight and preferably less than 0.03% by weight. If Zr is not chosen, its content is less than 0.04% by weight and preferably less than 0.02% by weight.
The products according to the invention have satisfactory properties in terms of compromise between mechanical strength and toughness and very advantageous properties in terms of speed of crack propagation in fatigue and in terms of sensitivity to crack deflection. Thus, advantageously the products according to the invention have,
  1. (i) for a thickness between 50 and 75 mm, at quarter thickness, an elastic limit R p0,2 (TL) ≥ 435 MPa and preferably R p0,2 (TL) ≥ 455 MPa and a toughness K 1C (TL) ≥ 28 MPa√m and advantageously such that K 1C (TL) ≥ 30 MPa√m,
  2. (ii) for a thickness between 76 and 102 mm, at quarter thickness, an elastic limit R p0,2 (TL) ≥ 435 MPa and preferably R p0,2 (TL) ≥ 455 MPa and a toughness K 1C (TL) ≥ 25 MPa√m and advantageously such that K 1C (TL) ≥ 27 MPa√m.
  3. (iii) for a thickness between 103 and 130 mm, at quarter thickness, an elastic limit R p0,2 (TL) ≥ 428 MPa and preferably R p0,2 (TL) ≥ 448 MPa and a toughness K 1C (TL) ≥ 23 MPa√m and advantageously such that K 1C (TL) ≥ 25 MPa√m.
  4. (iv) for a thickness greater than 130 mm, at quarter thickness, an elastic limit R p0,2 (TL) ≥ 428 MPa and preferably R p0,2 (TL) ≥ 448 MPa and a toughness K 1C ( TL) ≥ 21 MPa√m and advantageously such that K 1C (TL) ≥ 23 MPa√m,
and they have a crack propagation speed measured according to standard ASTM E647 on CCT specimens, with central crack, of width 100 mm and thickness 6.35 mm taken at mid-thickness in the LS orientation less than 10 -4 mm / cycle for a ΔK = 20 MPa√m and preferably less than 9.10 -5 mm / cycle for a ΔK = 20 MPa√m.

Les produits selon l'invention présentent également des propriétés avantageuses en termes de propension à la bifurcation de fissure. La bifurcation macroscopique de fissures lors de tests en fatigue dans la direction L-S, de la direction S vers la direction L a été évaluée de deux façons. Dans une première méthode, au moins 6 éprouvettes L-S CT, d'épaisseur 10 mm et de largeur totale 50 mm (40 mm entre l'axe des trous et la face arrière de l'éprouvette) réalisées selon la Figure 1 sont testées en fatigue à la charge maximale d'au moins 3000 N, et un rapport de charge de R = 0.1, permettant de couvrir au cours de l'essai le domaine de ΔK allant de 10 à 40 MPa√m, où ΔK est la variation du facteur d'intensité de contrainte dans un cycle de charge. On observe sur les éprouvettes la face dans laquelle a lieu la rupture. Ceci est illustré par la Figure 5. Lorsque la rupture a lieu par la face arrière (1), comme pour la figure 5A, la bifurcation de fissure a été faible. Lorsque la rupture a lieu par la face supérieure (21) ou inférieure (22), comme pour la figure 5B ou 5C, la bifurcation de fissure a été plus significative. Pour les produits selon l'invention la propension à la bifurcation de fissure est faible et la rupture lors d'un test de fatigue dans la direction L - S à une charge maximale d'au moins 3000 N, R = 0,1, sur un lot d'au moins 6 éprouvettes CT d'épaisseur 10 mm et de largeur totale 50 mm se fait majoritairement par la face arrière.
Dans une seconde méthode, on évalue la propension à la bifurcation de fissure en mesurant la distance d sur laquelle la fissure n'est ni dans la direction S initiale, ni dans la direction L, pour une éprouvette L-S CT, d'épaisseur 10 mm et de largeur totale 50 mm réalisée selon la Figure 1 et sont testées en fatigue à la charge maximale d'au moins 3000 N, et un rapport de charge de R = 0.1. La figure 5c montre un exemple d'évaluation de cette distance : lorsque la fissure dévie, elle ne rejoint pas tout de suite la direction L et on peut ainsi mesurer la distance d. On considère que la fissure est dans la direction S ou de la direction L quand elle ne dévie pas de cette direction de plus de 10°. Pour les produits selon l'invention la propension à la bifurcation de fissure est faible et lors d'un test de fatigue dans la direction L - S à une charge maximale d'au moins 3000 N, R = 0,1, sur une éprouvette CT d'épaisseur 10 mm et de largeur totale 50 mm la distance d sur laquelle la fissure n'est ni dans la direction S initiale, ni dans la direction L est au moins 5 mm et de préférence au moins 10 mm.The products according to the invention also have advantageous properties in terms of propensity to crack bifurcation. The macroscopic bifurcation of cracks during fatigue tests in the LS direction, from the S direction to the L direction was evaluated in two ways. In a first method, at least 6 LS CT test pieces, 10 mm thick and 50 mm total width (40 mm between the axis of the holes and the rear face of the test piece) produced according to the Figure 1 are tested in fatigue at the maximum load of at least 3000 N, and a load ratio of R = 0.1, making it possible to cover during the test the range of ΔK ranging from 10 to 40 MPa√m, where ΔK is the variation of the stress intensity factor in a charge cycle. The side in which the rupture takes place is observed on the test pieces. This is illustrated by the Figure 5 . When the rupture takes place from the rear face (1), as for the figure 5A , the crack bifurcation was small. When the rupture takes place by the upper (21) or lower (22) face, as for the figure 5B or 5C , the crack bifurcation was more significant. For the products according to the invention the propensity for crack bifurcation is low and the rupture during a fatigue test in the direction L - S at a maximum load of at least 3000 N, R = 0.1, on a batch of at least 6 CT specimens with a thickness of 10 mm and a total width of 50 mm is mainly made by the rear face.
In a second method, the propensity for crack bifurcation is evaluated by measuring the distance d over which the crack is neither in the initial S direction, nor in the L direction, for a LS CT specimen, 10 mm thick. and a total width of 50 mm made according to the Figure 1 and are tested in fatigue at the maximum load of at least 3000 N, and a load ratio of R = 0.1. The figure 5c shows an example of evaluation of this distance: when the crack deviates, it does not immediately join the direction L and one can thus measure the distance d. One considers that the crack is in direction S or direction L when it does not deviate from this direction by more than 10 °. For the products according to the invention the propensity for crack bifurcation is low and during a fatigue test in the direction L - S at a maximum load of at least 3000 N, R = 0.1, on a test piece CT of thickness 10 mm and total width 50 mm the distance d over which the crack is neither in the initial direction S nor in the direction L is at least 5 mm and preferably at least 10 mm.

Le procédé de fabrication d'une tôle de structure granulaire majoritairement recristallisée d'épaisseur au moins 50 mm selon l'invention comprend les étapes de coulée, homogénéisation, laminage à chaud, mise en solution, trempe, traction contrôlée et revenu.
Un alliage contenant des quantités contrôlées selon l'invention d'éléments d'alliage est coulé sous forme de plaque.
La plaque est homogénéisée à une température d'au moins 490 °C. De préférence la durée d'homogénéisation est au moins 12 heures. L'homogénéisation peut être réalisée en un ou plusieurs paliers. Selon le premier mode de réalisation de l'invention, l'homogénéisation comprend au moins une étape dont la température est d'au moins 520 °C et de préférence au moins 530 °C, la durée pendant laquelle la température est supérieure à 520 °C étant au moins 20 heures et de préférence au moins 30 heures.
Une étape de laminage à chaud est réalisée après réchauffage si nécessaire pour obtenir des tôles dont l'épaisseur est d'au moins 50 mm. Selon le premier mode de réalisation de l'invention la température de sortie de laminage à chaud est inférieure à 390 °C, préférentiellement inférieure à 380 °C. La combinaison notamment des conditions de l'étape d'homogénéisation et de l'étape de laminage à chaud du premier mode de réalisation permet d'obtenir une structure finale après revenu majoritairement recristallisée notamment pour des produits dont la somme de la teneur des éléments Zr, Cr, Sc, Hf, et V est au moins 0,08 % en poids. De manière surprenante, les inventeurs ont constaté que les conditions selon ce premier mode de réalisation permettent de diminuer la propension à la bifurcation de fissure.
Selon le second mode de réalisation, la somme de la teneur des éléments Zr, Cr, Sc, Hf, et V est inférieure à 0,08 % en poids et la température de sortie de laminage à chaud est de préférence d'au moins 400 °C et de préférence d'au moins 420 °C.
Les tôles sont mises en solution par chauffage entre 490 et 540 °C préférentiellement pendant 15 minutes à 4 heures, les paramètres de mise en solution dépendant de l'épaisseur du produit. Une trempe à l'eau froide est réalisée après mise en solution.
Le produit subit ensuite une traction contrôlée avec une déformation permanente comprise entre 1% et 7% et de préférence entre 2% et 6%. Le revenu est réalisé à une température comprise entre 130 °C et 170 °C et de préférence à une température comprise entre 140 °C et 160 °C pendant une durée de 5 à 60 heures, ce qui résulte en un état T8. Dans certains cas, et en particulier pour certaines compositions préférées, le revenu est réalisé de manière préférée entre 140 et 160 °C pendant 12 à 50 heures.The process for manufacturing a mainly recrystallized granular sheet with a thickness of at least 50 mm according to the invention comprises the steps of casting, homogenization, hot rolling, dissolution, quenching, controlled traction and tempering.
An alloy containing controlled quantities according to the invention of alloying elements is cast in the form of a plate.
The plate is homogenized at a temperature of at least 490 ° C. Preferably the homogenization time is at least 12 hours. Homogenization can be carried out in one or more stages. According to the first embodiment of the invention, the homogenization comprises at least one step whose temperature is at least 520 ° C and preferably at least 530 ° C, the period during which the temperature is above 520 ° C being at least 20 hours and preferably at least 30 hours.
A hot rolling step is carried out after reheating if necessary to obtain sheets whose thickness is at least 50 mm. According to the first embodiment of the invention, the hot rolling outlet temperature is less than 390 ° C, preferably less than 380 ° C. The combination in particular of the conditions of the homogenization step and of the hot rolling step of the first embodiment makes it possible to obtain a final structure after mostly recrystallized tempering, in particular for products whose sum of the content of the elements Zr , Cr, Sc, Hf, and V is at least 0.08% by weight. Surprisingly, the inventors have found that the conditions according to this first embodiment make it possible to reduce the propensity for crack bifurcation.
According to the second embodiment, the sum of the content of the elements Zr, Cr, Sc, Hf, and V is less than 0.08% by weight and the outlet temperature from hot rolling is preferably at least 400 ° C and preferably at least 420 ° C.
The sheets are dissolved by heating between 490 and 540 ° C, preferably for 15 minutes to 4 hours, the dissolution parameters depending on the thickness of the product. Cold water quenching is carried out after dissolution.
The product then undergoes controlled traction with a permanent deformation of between 1% and 7% and preferably between 2% and 6%. Tempering is carried out at a temperature between 130 ° C and 170 ° C and preferably at a temperature between 140 ° C and 160 ° C for a period of 5 to 60 hours, which results in a T8 state. In certain cases, and in particular for certain preferred compositions, the tempering is carried out preferably between 140 and 160 ° C. for 12 to 50 hours.

Les produits selon l'invention sont avantageusement utilisés dans la construction aéronautique. L'utilisation des produits selon l'invention pour la réalisation d'un longeron d'aile d'avion ou d'une nervure d'aile d'avion est particulièrement avantageuse. L'utilisation des produits selon l'invention pour la réalisation d'un longeron d'aile d'avion est préférée, avantageusement pour la partie inférieure, c'est-à-dire en liaison avec l'intrados de l'aile, d'un longeron soudé.The products according to the invention are advantageously used in aeronautical construction. The use of the products according to the invention for producing an aircraft wing spar or an aircraft wing rib is particularly advantageous. The use of the products according to the invention for the production of an aircraft wing spar is preferred, advantageously for the lower part, that is to say in connection with the lower surface of the wing, d '' a welded beam.

ExemplesExamples Exemple 1Example 1

Cinq plaques en alliage Al-Cu-Li référencées A, B, C, D et E, ont été coulées. Leur composition est donnée dans le Tableau 1. Tableau 1. Composition (% en poids) des différentes plaques. Si Fe Cu Mn Mg Ti Zr Li Ag Zn A 0.03 0.04 3.57 0.38 0.33 0.03 0.08 0.87 0.35 0.05 B 0.03 0.04 3.59 0.38 0.33 0.03 0.08 0.92 0.36 0.03 C 0.03 0.04 3.68 0.38 0.34 0.03 0.08 0.92 0.38 0.04 D 0.02 0.01 3.50 0.55 0.33 0.03 0.08 0.88 0.36 0.04 E 0.03 0.05 3.53 0.38 0.40 0.03 0.09 0.89 0.38 <0.05 Five Al-Cu-Li alloy plates referenced A, B, C, D and E, were cast. Their composition is given in Table 1. Table 1. Composition (% by weight) of the various plates. Yes Fe Cu Mn Mg Ti Zr Li Ag Zn AT 0.03 0.04 3.57 0.38 0.33 0.03 0.08 0.87 0.35 0.05 B 0.03 0.04 3.59 0.38 0.33 0.03 0.08 0.92 0.36 0.03 VS 0.03 0.04 3.68 0.38 0.34 0.03 0.08 0.92 0.38 0.04 D 0.02 0.01 3.50 0.55 0.33 0.03 0.08 0.88 0.36 0.04 E 0.03 0.05 3.53 0.38 0.40 0.03 0.09 0.89 0.38 <0.05

La plaque A a été homogénéisée en deux paliers de 36 heures à 504 °C puis 48 heures à 530 °C. Les plaques B et C ont été homogénéisée en deux paliers de 8 heures à 496 °C puis 34 heures à 530 °C. La plaque D a été homogénéisée 12 heures à 505°C. La plaque E a été homogénéisée en deux paliers 8h à 500 °C puis 36 heures à 527 °C.Plate A was homogenized in two stages of 36 hours at 504 ° C and then 48 hours at 530 ° C. Plates B and C were homogenized in two steps of 8 hours at 496 ° C and then 34 hours at 530 ° C. Plate D was homogenized for 12 hours at 505 ° C. Plate E was homogenized in two stages 8 h at 500 ° C and then 36 hours at 527 ° C.

La plaque A a été laminée à chaud jusqu'à une tôle d'épaisseur 100 mm, la température d'entrée de laminage à chaud était 410 °C et la température de sortie de laminage à chaud était 361 °C. La plaque B a été laminée à chaud jusqu'à une tôle d'épaisseur 102 mm , la température d'entrée de laminage à chaud était 406 °C et la température de sortie de laminage à chaud était 350 °C. La plaque C a été laminée à chaud jusqu'à une tôle d'épaisseur 102 mm , la température d'entrée de laminage à chaud était 410 °C et la température de sortie de laminage à chaud était 360 °C. La plaque D a été laminée à chaud jusqu'à une tôle d'épaisseur 100 mm, la température d'entrée de laminage à chaud était 505°C et la température de sortie de laminage à chaud était 520°C.Plate A was hot rolled to a 100 mm thick sheet, the hot rolling inlet temperature was 410 ° C and the hot rolling outlet temperature was 361 ° C. Plate B was hot rolled to a 102 mm thick sheet, the hot rolling inlet temperature was 406 ° C and the hot rolling outlet temperature was 350 ° C. Plate C was hot rolled to a 102 mm thick sheet, the hot rolling inlet temperature was 410 ° C and the hot rolling outlet temperature was 360 ° C. Plate D was hot rolled to a 100 mm thick sheet, the hot rolling inlet temperature was 505 ° C and the hot rolling outlet temperature was 520 ° C.

La plaque E a été laminée à chaud jusqu'à une tôle d'épaisseur 100 mm, la température d'entrée de laminage à chaud était 481°C et la température de sortie de laminage à chaud était 460°C.Plate E was hot rolled to a 100 mm thick sheet, the hot rolling inlet temperature was 481 ° C and the hot rolling outlet temperature was 460 ° C.

Les tôles ainsi obtenues ont été mises en solution pendant 2 heures à 525 °C et trempées avec de l'eau froide.
Les tôles ainsi mises en solution et trempées ont été tractionnées de façon contrôlée, avec un allongement permanent de 4% et ont subi un revenu de 18 heures à 155 °C (A, B, C et E) ou 24 h à 155°C (D).The sheets thus obtained were dissolved for 2 hours at 525 ° C and quenched with cold water.
The sheets thus dissolved and quenched were pulled in a controlled manner, with a permanent elongation of 4% and underwent an 18 hour tempering at 155 ° C (A, B, C and E) or 24 h at 155 ° C (D).

Le taux de recristallisation des tôles ainsi obtenues a été mesuré sur des coupes micrographiques de surface 0,5 x 1 mm2 dans le plan L-TC à diverses positions dans l'épaisseur. Les résultats obtenus sont présentés dans le Tableau 2. Tableau 2 : Mesures du taux de recristallisation (%) A B C D E ¼ Epaisseur 67 75 72 13 < 15 ½ Epaisseur 60 58 60 5 < 15 The recrystallization rate of the sheets thus obtained was measured on micrographic sections of surface 0.5 × 1 mm 2 in the L-TC plane at various positions in the thickness. The results obtained are presented in Table 2. Table 2: Measures of the recrystallization rate (%) AT B VS D E ¼ Thickness 67 75 72 13 <15 ½ Thickness 60 58 60 5 <15

Des échantillons ont été testés mécaniquement pour déterminer leurs propriétés mécaniques statiques et leur ténacité. La résistance à la rupture Rm, la limite d'élasticité conventionnelle à 0,2% d'allongement Rp0,2 et l'allongement à la rupture A sont données dans le Tableau 3 et la ténacité K1C est donnée dans le tableau 4. Tableau 3. Propriétés mécaniques statiques mesurées à ¼ épaisseur (T/4) et à mi-épaisseur (T/2). Echantillon T/4 T/2 L TL L TL Rm MPa Rp0,2 MPa A (%) Rm MPa Rp0,2 MPa A (%) Rm MPa Rp0,2 MPa A (%) Rm MPa Rp0,2 MPa A (%) A 514 480 6.2 519 465 7.2 511 477 7.5 505 453 8.8 B C 516 483 9.2 516 458 6.3 523 492 8.6 500 449 6.1 D 509 478 11.3 517 460 9.3 E 527 492 9.6 527 459 7.0 530 492 9.5 505 444 6.9 Tableau 4 . Facteur d'intensité de contrainte (K1C) mesuré à ¼ épaisseur (T/4) et à mi-épaisseur (T/2) déterminé selon la norme ASTM E 399. K1c MPa√m) Echantillon T/4 T/2 L-T T-L S-L L-S A 32.3 35.1 B C 36.0 29.1 27.7 48.9* D 40.0* 32.9 31.2 E 37.7 29.8 31.0 * Déviation de fissure à 90° Samples were tested mechanically to determine their static mechanical properties and their toughness. The breaking strength R m , the conventional yield strength at 0.2% elongation R p0.2 and the elongation at break A are given in Table 3 and the toughness K 1C is given in the table 4. Table 3. Static mechanical properties measured at ¼ thickness (T / 4) and mid-thickness (T / 2). Sample T / 4 T / 2 L TL L TL R m MPa R p0.2 MPa AT (%) R m MPa R p0.2 MPa AT (%) R m MPa R p0.2 MPa AT (%) R m MPa R p0.2 MPa AT (%) AT 514 480 6.2 519 465 7.2 511 477 7.5 505 453 8.8 B VS 516 483 9.2 516 458 6.3 523 492 8.6 500 449 6.1 D 509 478 11.3 517 460 9.3 E 527 492 9.6 527 459 7.0 530 492 9.5 505 444 6.9 K 1c MPa√m) Sample T / 4 T / 2 LT TL SL LS AT 32.3 35.1 B VS 36.0 29.1 27.7 48.9 * D 40.0 * 32.9 31.2 E 37.7 29.8 31.0 * 90 ° crack deviation

Des essais de propagation de fissure en fatigue sur des éprouvettes L-S ont été réalisés sur des échantillons provenant des tôles C et E. Les essais ont été réalisés selon la norme ASTM E647. Ces essais sont réalisés sur éprouvettes CCT, à fissure centrale, de largeur 100 mm et d'épaisseur 6.35 mm.Fatigue crack propagation tests on L-S test pieces were carried out on samples from sheets C and E. The tests were carried out according to standard ASTM E647. These tests are carried out on CCT specimens, with central crack, of width 100 mm and thickness 6.35 mm.

La figure 2 montre les résultats de vitesse de propagation de fissure pour les échantillons testés avec l'éprouvette CCT. Les résultats sont résumés dans le Tableau 5 ci-dessous. Tableau 5. Résultats des essais de propagation de fissure en fatigue éprouvettes L-S selon la norme ASTM E647. C E da/dn pour ΔK = 10 MPa√m [mm/cycle] 6.5 10-5 1.2 10-4 da/dn pour ΔK = 20 MPa√m [mm/cycle] 8.0 10-5 1.4 10-4 da/dn pour ΔK = 30 MPa√m [mm/cycle] 1.5 10-4 2.2 10-4 The figure 2 shows the crack propagation velocity results for the samples tested with the CCT specimen. The results are summarized in Table 5 below. Table 5. Results of the crack propagation fatigue testing of LS test pieces according to ASTM E647. VS E da / dn for ΔK = 10 MPa√m [mm / cycle] 6.5 10 -5 1.2 10 -4 da / dn for ΔK = 20 MPa√m [mm / cycle] 8.0 10 -5 1.4 10 -4 da / dn for ΔK = 30 MPa√m [mm / cycle] 1.5 10 -4 2.2 10 -4

En outre, pour examiner la susceptibilité à la déviation de fissure, 6 échantillons L-S selon la Figure 1 ont été prélevés dans les tôles A (échantillons A1, A2, B1, B2, C1, C2) et D (échantillons 84A1, 84A2, 84B1, 84B2, 84C1, 84C2) et soumis à un essai en propagation en fatigue à la charge maximale de 4000 N, ou 3000 N lorsque spécifié, et un rapport de charge de R = 0.1. Les repères 84A2 et A2, B2 et C2 ont été testés à 3000 N de force maximale plutôt que 4000 N. Les conditions permettent de couvrir au cours de l'essai le domaine de ΔK allant de 10 à 40 MPa√m, où ΔK est la variation du facteur d'intensité de contrainte dans un cycle de charge. Sur cette autre géométrie la différence de vitesse de propagation de fissure entre l'alliage recristallisé et l'alliage non recristallisé est illustrée par la Figure 4.
Les figures 3a et 3b montrent, respectivement, les échantillons issus des tôles A et D après l'essai en fatigue. Les échantillons issus de la tôle A selon l'invention présentent une bifurcation de fissure progressive avec dans 4 cas sur 6 (C1, C2, B1, A2) une rupture par la face arrière de l'éprouvette. La distance d sur laquelle la fissure n'est ni dans la direction S initiale, ni dans la direction L est au moins 15 mm pour tous les échantillons issus de la tôle A, car dans aucun des cas la fissure ne rejoint la direction L. Tous les échantillons issus de la tôle D présentent une propension élevée à la bifurcation de fissure avec une rupture toujours par la face supérieure ou la face inférieure de l'éprouvette et une distance d sur laquelle la fissure n'est ni dans la direction S initiale, ni dans la direction L inférieure à 3 mm : pour tous les échantillons la fissure passe directement de la direction S initiale à la direction L perpendiculaire.In addition, to examine the susceptibility to crack deviation, 6 LS samples according to the Figure 1 were taken from sheets A (samples A1, A2, B1, B2, C1, C2) and D (samples 84A1, 84A2, 84B1, 84B2, 84C1, 84C2) and subjected to a fatigue propagation test at maximum load 4000 N, or 3000 N when specified, and a charge ratio of R = 0.1. The marks 84A2 and A2, B2 and C2 were tested at 3000 N of maximum force rather than 4000 N. The conditions make it possible during the test to cover the range of ΔK ranging from 10 at 40 MPa√m, where ΔK is the variation of the stress intensity factor in a charge cycle. On this other geometry the difference in crack propagation speed between the recrystallized alloy and the non-recrystallized alloy is illustrated by the Figure 4 .
The figures 3a and 3b show, respectively, the samples from sheets A and D after the fatigue test. The samples from sheet A according to the invention exhibit a progressive crack bifurcation with in 4 out of 6 cases (C1, C2, B1, A2) a rupture by the rear face of the test piece. The distance d over which the crack is neither in the initial S direction, nor in the L direction is at least 15 mm for all samples from sheet A, because in none of the cases does the crack join the direction L. All the samples coming from sheet D have a high propensity for crack bifurcation with a rupture always by the upper face or the lower face of the specimen and a distance d over which the crack is neither in the initial direction S , nor in the direction L less than 3 mm: for all the samples the crack passes directly from the direction S initial to the direction L perpendicular.

La figure 4 montre les résultats de vitesse de propagation mesurés par la méthode de l'ouverture de la fissure, lors des essais sur éprouvettes CT. Ces essais montrent également que la vitesse de propagation est nettement plus lente, dans le sens L-S, pour la tôle A selon l'invention.The figure 4 shows the propagation speed results measured by the crack opening method, during tests on CT specimens. These tests also show that the propagation speed is significantly slower, in the LS direction, for sheet A according to the invention.

Le produit majoritairement recristallisé selon l'invention présente une propagation de fissures en fatigue particulièrement avantageuse.The mainly recrystallized product according to the invention has a particularly advantageous propagation of fatigue cracks.

Exemple 2Example 2

Trois plaques en alliage Al-Cu-Li référencées F, G et H ont été coulées. Leur composition est donnée dans le Tableau 6. Tableau 6. Composition (% en poids) des différentes plaques. Si Fe Cu Mn Mg Ti Zr Li Ag F 0.03 0.04 3.04 0.28 0.44 0.03 - 0.71 0.22 G 0.03 0.04 3.61 0.37 0.35 0.03 0.06 0.88 0.36 H 0.03 0.05 3.55 0.38 0.32 0.03 0.08 0.87 0.36 Three Al-Cu-Li alloy plates referenced F, G and H were cast. Their composition is given in Table 6. Table 6. Composition (% by weight) of the various plates. Yes Fe Cu Mn Mg Ti Zr Li Ag F 0.03 0.04 3.04 0.28 0.44 0.03 - 0.71 0.22 G 0.03 0.04 3.61 0.37 0.35 0.03 0.06 0.88 0.36 H 0.03 0.05 3.55 0.38 0.32 0.03 0.08 0.87 0.36

Des échantillons de format 14 mm x 50 mm x 56 mm ont été usinés à mi-largeur (L/2) et quart-épaisseur (T/4) des plaques de coulée. La figure 6 présente de tels échantillons d'épaisseur C 14 mm et de largueur B 50 mm. Les échantillons ont été homogénéisés en deux paliers de 5 heures à 505 °C puis 12 heures à 525 °C.Samples of format 14 mm x 50 mm x 56 mm were machined at half-width (L / 2) and quarter-thickness (T / 4) of the casting plates. The figure 6 presents such samples of thickness C 14 mm and width B 50 mm. The samples were homogenized in two stages of 5 hours at 505 ° C and then 12 hours at 525 ° C.

Les échantillons ont été déformés à chaud par bipoinçonnement à l'aide d'une machine de type « Servotest » ®, la température et la vitesse de déformation étaient respectivement 400 °C et 1s-1. La figure 6 illustre une telle déformation par bipoinçonnement. L'épaisseur finale de la portion déformée de largueur W (W=15 mm) était de 3.6mm, ce qui représente une réduction totale d'environ 74%. Une telle déformation est représentative d'une déformation industrielle par laminage à chaud d'une plaque de fonderie d'environ 400 mm à une épaisseur finale d'environ 100 mm.The samples were hot deformed by double punching using a "Servotest" ® type machine, the temperature and the speed of deformation were 400 ° C and 1s -1 respectively . The figure 6 illustrates such a deformation by double-punching. The final thickness of the deformed portion of width W (W = 15 mm) was 3.6 mm, which represents a total reduction of approximately 74%. Such a deformation is representative of an industrial deformation by hot rolling of a foundry plate of approximately 400 mm to a final thickness of approximately 100 mm.

Les échantillons ainsi obtenus ont été mis en solution pendant 2 heures à 525 °C puis trempés à l'eau froide et ont subi un revenu.The samples thus obtained were dissolved for 2 hours at 525 ° C then quenched in cold water and subjected to tempering.

Le taux de recristallisation à mi-épaisseur des échantillons a été évalué sur des coupes micrographiques de surface 0,5 x 1 mm2 dans le plan L-TC . Les résultats obtenus sont présentés dans le Tableau 7. Tableau 7 : Mesure du taux de recristallisation (%) F G H ½ Epaisseur 100 70 48 The recrystallization rate at mid-thickness of the samples was evaluated on micrographic sections of surface 0.5 × 1 mm 2 in the L-TC plane. The results obtained are presented in Table 7. Table 7: Measurement of the recrystallization rate (%) F G H ½ Thickness 100 70 48

Les échantillons F et G sont majoritairement recristallisés.The samples F and G are mainly recrystallized.

Claims (10)

  1. Rolled product having a thickness of at least 50 mm made of aluminium alloy comprising as a % by weight 2.2 to 3.9% Cu, 0.7 to 1.8% Li, 0.1 to 0.8% Mg, 0.1 to 0.6 % Mn; 0.01 to 0.15% Ti, at least one element chosen from Zn and Ag, the quantity of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, optionally at least one element chosen from Zr, Cr, Sc, Hf, and V, the quantity of said element if it is chosen being 0.04 to 0.18% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V, less than 0.1% Fe, less than 0.1% Si the remainder aluminium and unavoidable impurities, of a content less than 0.05% each and 0.15% in total; characterised in that the granular structure thereof is mostly recrystallised between the ¼ and ½ thickness.
  2. Rolled product according to claim 1 characterised in that the thickness thereof is between 80 and 130 mm.
  3. Rolled product according to claim 1 or claim 2 characterised in that the maximum Li content is 1.5% by weight.
  4. Rolled product according to any one of claims 1 to 3 characterised in that the sum of the Zr, Cr, Sc, Hf, and V element content is less than 0.08% by weight.
  5. Rolled product according to any one of claims 1 to 4 having
    (i) for a thickness between 50 and 75 mm, at quarter-thickness, a yield strength Rp0.2(TL) ≥ 435 MPa and preferably Rp0.2(TL) ≥ 455 MPa and a toughness K1C (T-L) ≥ 28 MPa√m and advantageously such that K1C (T-L) ≥ 30 MPa√m,
    (ii) for a thickness between 76 and 102 mm, at quarter-thickness, a yield strength Rp0.2(TL) ≥ 435 MPa and preferably Rp0.2(TL) ≥ 455 MPa and a toughness K1C (T-L) ≥ 25 MPa√m and advantageously such that K1C (T-L) ≥ 27 MPa√m.
    (iii) for a thickness between 103 and 130 mm, at quarter-thickness, a yield strength Rp0.2(TL) ≥ 428 MPa and preferably Rp0.2(TL) ≥ 448 MPa and a toughness K1C (T-L) ≥ 23 MPa√m and advantageously such that K1C (T-L) ≥ 25 MPa√m.
    (iv) for a thickness greater than 130 mm, at quarter-thickness, a yield strength Rp0.2(TL) ≥ 428 MPa and preferably Rp0.2(TL) ≥ 448 MPa and a toughness K1C (T-L) ≥ 21 MPa√m and advantageously such that K1C (T-L) ≥ 23 MPa√m,
    and having a fatigue crack growth rate measured as per the standard ASTM E647 on CCT centre cracked test specimens, 100 mm in width and 6.35 mm in thickness sampled at mid-thickness in the L-S orientation less than 10-4 mm/cycle for a ΔK = 20 MPa√m.
  6. Rolled product according to any one of claims 1 to 5 exhibiting a low tendency to crack branching characterised in that the fracture during a fatigue test in the L - S direction at a maximum load of at least 3000 N, R = 0.1, on a lot of at least 6 CT test specimens 10 mm in thickness and 50 mm in total thickness occurs mostly via the rear side (1).
  7. Rolled product according to any one of claims 1 to 6 exhibiting a low tendency to crack branching characterised in that during a fatigue test in the L - S direction at a maximum load of at least 3000 N, R = 0.1, on a CT test specimen 10 mm in thickness and 50 mm in total width the distance d whereon the crack is neither in the initial S direction, nor in the L direction is at least 5 mm and preferably at least 10 mm.
  8. Process for manufacturing a sheet according to any one of claims 1 to 7, comprising:
    a) casting a rolling ingot, made of aluminium alloy comprising as a % by weight 2.2 to 3.9% Cu, 0.7 to 1.8% Li, 0.1 to 0.8% Mg, 0.1 to 0.6% Mn; 0.01 to 0.15% Ti, at least one element chosen from Zn and Ag, the quantity of said element if it is chosen being 0.2 to 0.8% for Zn and 0.1 to 0.5% for Ag, optionally at least one element chosen from Zr, Cr, Sc, Hf, and V, the quantity of said element if it is chosen being 0.04 to 0.18% for Zr, 0.05 to 0.3% for Cr and for Sc, 0.05 to 0.5% for Hf and for V, less than 0.1% Fe, less than 0.1% Si the remainder aluminium and unavoidable impurities, of a content less than 0.05% each and 0.15% in total;
    b) homogenising said rolling ingot at a temperature of at least 490°C,
    c) hot rolling said rolling ingot to obtain a sheet of at least 50 mm in thickness,
    d) solution heat treatment between 490°C and 540°C,
    e) quenching in cold water,
    f) controlled stretching of said sheet by heating said sheet with a permanent set of 1 to 7%,
    g) aging said sheet by heating between 130°C and 170°C for 5 to 60 hours,
    characterised in that the sum of the Zr, Cr, Sc, Hf, and V element content is less than 0.08% by weight and/or in that during step b) the homogenising comprises at least one step wherein the temperature is at least 520°C, the time during which the temperature is greater than 520°C being at least 20 hours and during step c) the hot rolling output temperature is less than 390°C.
  9. Use of a sheet according to any one of claims 1 to 7 for producing an aircraft wing spar or an aircraft wing rib.
  10. Use according to claim 9 for the bottom part of a welded spar.
EP17707940.7A 2016-02-03 2017-02-03 Thick al - cu - li - alloy sheets having improved fatigue properties Active EP3411508B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR1650850A FR3047253B1 (en) 2016-02-03 2016-02-03 AL-CU-LI THICK-ALLOY TILES WITH IMPROVED FATIGUE PROPERTIES
PCT/FR2017/050255 WO2017134405A1 (en) 2016-02-03 2017-02-03 Thick plates made of al-cu-li alloy with improved fatigue properties

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EP3411508A1 EP3411508A1 (en) 2018-12-12
EP3411508B1 true EP3411508B1 (en) 2020-04-08

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US20190233921A1 (en) * 2018-02-01 2019-08-01 Kaiser Aluminum Fabricated Products, Llc Low Cost, Low Density, Substantially Ag-Free and Zn-Free Aluminum-Lithium Plate Alloy for Aerospace Application
FR3080861B1 (en) * 2018-05-02 2021-03-19 Constellium Issoire METHOD OF MANUFACTURING AN ALUMINUM COPPER LITHIUM ALLOY WITH IMPROVED COMPRESSION RESISTANCE AND TENACITY
CN113943880A (en) * 2021-10-15 2022-01-18 西南铝业（集团）有限责任公司 Al-Cu-Li-Mg-V-Zr-Sc-Ag alloy and preparation method thereof
CN115433888B (en) * 2022-08-18 2023-06-13 哈尔滨工业大学（深圳） Thermomechanical treatment method for aluminum lithium alloy medium plate

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CA3012956A1 (en) 2017-08-10
FR3047253A1 (en) 2017-08-04
CN108603253B (en) 2021-03-19
FR3047253B1 (en) 2018-01-12
US20240035138A1 (en) 2024-02-01
CA3012956C (en) 2023-10-03
BR112018014770A2 (en) 2018-12-18
WO2017134405A1 (en) 2017-08-10
US20190040508A1 (en) 2019-02-07
EP3411508A1 (en) 2018-12-12
BR112018014770B1 (en) 2022-11-16
CN108603253A (en) 2018-09-28

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