EP3802897B1 - Thin sheets made of aluminium-copper-lithium alloy for aircraft fuselage manufacture - Google Patents

Thin sheets made of aluminium-copper-lithium alloy for aircraft fuselage manufacture Download PDF

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EP3802897B1
EP3802897B1 EP19740635.8A EP19740635A EP3802897B1 EP 3802897 B1 EP3802897 B1 EP 3802897B1 EP 19740635 A EP19740635 A EP 19740635A EP 3802897 B1 EP3802897 B1 EP 3802897B1
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sheet
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EP3802897A1 (en
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Pablo LORENZINO
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Constellium Issoire SAS
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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
    • 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
    • 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
    • C22C21/16—Alloys based on aluminium with copper as the next major constituent with magnesium

Definitions

  • the invention relates to rolled aluminum-copper-lithium alloy products, more particularly, such products, their methods of manufacture and use, intended in particular for aeronautical and aerospace construction.
  • Rolled aluminum alloy products are developed to produce fuselage components intended in particular for the aeronautical and aerospace industries.
  • Aluminum-copper-lithium alloys are particularly promising for manufacturing this type of product.
  • the patent US 5,455,003 describes a process for the manufacture of Al-Cu-Li alloys which exhibit improved mechanical strength and toughness at cryogenic temperature, in particular thanks to suitable work hardening and tempering.
  • the patent EP0584271 discloses an aluminum-based alloy useful in aircraft and aerospace structures, having low density, high strength and high fracture toughness, essentially corresponding to the formula CuaLibMgcAgdZreAlba1 in which a, b, c, d, e and bal indicate the percentage by weight of the alloying components, said percentages being 2.4 ⁇ a ⁇ 3.5, 1 .35 ⁇ b ⁇ 1.8, 0.25 ⁇ c ⁇ 0.65, 0.25 ⁇ d ⁇ 0.65 and 0.08 ⁇ e ⁇ 0.25.
  • 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 refiners such as Cr, Ti, Hf, Sc, V.
  • the patent application US 2011/0247730 describes alloys comprising (in % by weight), 2.75 to 5.0% Cu, 0.1 to 1.1% Li, 0.3 to 2.0% Ag, 0.2 to 0.8% Mg, 0 .50 to 1.5% Zn, up to 1.0% Mn, with a Cu/Mg ratio between 6.1 and 17, this alloy being insensitive to working.
  • the patent application CN101967588 describes alloys of composition (in % by weight) Cu 2.8 - 4.0; Li 0.8 - 1.9; Mn 0.2-0.6; Zn 0.20 - 0.80, Zr 0.04 - 0.20, Mg 0.20 - 0.80, Ag 0.1 - 0.7, Si ⁇ 0.10, Fe ⁇ 0.10, Ti ⁇ 0.12.
  • the patent FR3014448 describes a rolled and/or forged product whose thickness is between 14 and 100 mm, in aluminum alloy of composition, in% by weight, Cu: 1.8 - 2.6 Li: 1.3 - 1, 8 Mg: 0.1 - 0.5 Mn: 0.1 - 0.5 and Zr ⁇ 0.05 or Mn ⁇ 0.05 and Zr 0.10 - 0.16 10 Ag: 0 - 0.5 Zn ⁇ 0.20 Ti : 0.01 - 0.15 Fe: ⁇ 0.1 Si: ⁇ 0.1 15 other elements ⁇ 0.05 each and ⁇ 0.15 in total, rest aluminum whose density is less than 2.670 g/cm3 characterized in that at mid-thickness the volume fraction of the grains having a brass texture is between 25 and 40% and the texture index is between 12 and 18.
  • the patent application US2009084474 discloses a recrystallized aluminum alloy having a brass texture and a goss texture, where the amount of brass texture exceeds the amount of goss texture and where the recrystallized aluminum alloy has at least about the same yield strength and the same fracture toughness as an un-recrystallized alloy of the same product shape and similar thickness and temper.
  • the characteristics necessary for aluminum sheets intended for fuselage applications are in particular described, for example, in the patent EP 1 891 247 . It is particularly desirable for the sheet to have a high elastic limit (to resist buckling) as well as a toughness under high plane stress, characterized in particular by a high value of the stress intensity factor apparent at rupture (K app ) and a long R curve.
  • the patent EP 1 966 402 describes an alloy comprising 2.1 to 2.8 wt% Cu, 1.1 to 1.7 wt% Li, 0.1 to 0.8 wt% Ag, 0.2 to 0.6 % by weight of Mg, 0.2 to 0.6% by weight of Mn, an amount of Fe and Si less than or equal to 0.1% by weight each, and unavoidable impurities at a content less than or equal to 0 0.05% by weight each and 0.15% by weight in total, the alloy being substantially free of zirconium, particularly suitable for obtaining recrystallized thin sheets.
  • the longitudinal direction of the sheets being generally positioned in the direction of the length of the aircraft, these are constrained in the transverse direction by the pressure. The cracks are then stressed in the direction TL. It may also be advantageous for the sheets to have low anisotropy of mechanical properties, in particular between the L and TL directions.
  • Another object of the invention is a sheet obtained by the process according to the invention, the average grain size of which in the thickness measured by the method of intercepts on an L/TC section in the direction L according to the standard ASTM E112 and expressed in ⁇ m is less than 66 t + 200 where t is the thickness of the sheet expressed in mm.
  • Yet another object of the invention is the use of a thin sheet according to the invention in a fuselage panel for an aircraft.
  • the static mechanical characteristics in tension in other words the breaking 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 NF EN ISO 6892-1 (2016), the sampling and direction of the test being defined by standard EN 485-1 (2016).
  • the mechanical characteristics are measured at full thickness.
  • a curve giving the effective stress intensity factor as a function of the effective crack extension, known as the R-curve, is determined according to ASTM E 561.
  • the critical stress intensity factor Kc in other terms the intensity factor which makes the crack unstable, is calculated from the R curve.
  • the stress intensity factor K CO is also calculated by assigning the initial crack length at the beginning of the monotonic load, to the load critical. These two values are calculated for a specimen of the required shape.
  • K app represents the K CO factor corresponding to the specimen that was used to perform the R curve test.
  • K eff represents the Kc factor corresponding to the specimen that was used to perform the R curve test.
  • ⁇ a eff (max) represents the crack extension of the last point of the R-curve, valid according to ASTM E561.
  • the last point is obtained either at the moment of the sudden rupture of the specimen, or possibly at the moment when the stress on the uncracked ligament exceeds on average the elastic limit of the material.
  • the crack size at the end of the pre-fatigue cracking stage is W/3 for type M(T) specimens, where W is the width of the specimen as defined in the ASTM standard E561 (ASTM E561-10-2).
  • an essentially recrystallized granular structure is a granular structure such that the rate of recrystallization at 1 ⁇ 2 thickness is greater than 70% and preferably greater than 90%.
  • the recrystallization rate is defined as the fraction of area on a metallographic section occupied by recrystallized grains.
  • the thin sheets thus obtained have particularly advantageous properties, in particular as regards the toughness in the T-L direction and the anisotropy of the mechanical properties.
  • the copper content of the products according to the invention is between 2.3 and 2.7% by weight.
  • the copper content is at least 2.4% by weight, preferably at least 2.45% by weight and preferably at least 2.50% by weight.
  • the copper content is between 2.45 and 2.65% by weight and preferably between 2.50 and 2.60% by weight.
  • the copper content is at most 2.65% by weight and preferably at most 2.60% by weight.
  • the copper content is at most 2.53% by weight.
  • the lithium content of the products according to the invention is between 1.3 and 1.6% by weight.
  • the lithium content is between 1.35 and 1.55% by weight and preferably between 1.40% and 1.50% by weight.
  • a minimum lithium content of 1.35% by weight and preferably 1.40% by weight is advantageous.
  • a maximum lithium content of 1.55% by weight and preferably 1.50% by weight is advantageous, in particular to improve the compromise between toughness and mechanical strength.
  • the addition of lithium can contribute to the increase in mechanical strength and toughness, too high or too low a content does not make it possible to obtain a very high value of toughness in the T-L direction and/or a limit of sufficient elasticity.
  • the addition of lithium makes it possible to reduce the density.
  • the density of the products according to the invention is less than 2.65.
  • the magnesium content of the products according to the invention is between 0.2 and 0.5% by weight and preferably between 0.25 and 0.45% by weight and preferably between 0.25 and 0.35% in weight.
  • a minimum magnesium content of 0.25% by weight is advantageous.
  • a maximum magnesium content of 0.45% by weight and preferably 0.40% by weight and preferably 0.35% by weight or even 0.30% by weight is advantageous.
  • the manganese content is between 0.1 and 0.5% by weight, preferably between 0.2 and 0.4% by weight and preferably between 0.25 and 0.35% by weight.
  • a minimum manganese content of 0.2% by weight and preferably 0.25% by weight is advantageous.
  • a maximum manganese content of 0.4% by weight and preferably 0.35% by weight or even 0.33% by weight is advantageous.
  • the titanium content is between 0.01 and 0.15% by weight.
  • the iron and silicon contents are each at most 0.1% by weight.
  • the iron and silicon contents are at most 0.08% and preferably at most 0.04% by weight.
  • a controlled and limited iron and silicon content contributes to the improvement of the compromise between mechanical resistance and damage tolerance.
  • the zinc content is less than 0.3% by weight, preferably less than 0.2% by weight and preferably less than 0.1% by weight.
  • the zinc content is advantageously less than 0.04% by weight.
  • the unavoidable impurities are maintained at a content less than or equal to 0.05% by weight each and 0.15% by weight in total.
  • the process for manufacturing thin sheets according to the invention then comprises steps of casting, homogenization, hot and optionally cold rolling, solution treatment, controlled traction, quenching and tempering.
  • the formed liquid metal bath is cast in a rolling plate form.
  • the rolling plate is then homogenized at a temperature between 490°C and 535°C.
  • the homogenization time is between 5 and 60 hours.
  • the homogenization temperature is at least 500°C. In one embodiment, the homogenization temperature is less than 515°C.
  • the rolling plate After homogenization, the rolling plate is generally cooled to ambient temperature before being preheated in order to be hot deformed.
  • the purpose of the preheating is to reach a hot rolling inlet temperature of between 400 and 445° C. and preferably of between 420° C. and 440° C. allowing the deformation by hot rolling.
  • the hot rolling is carried out so as to obtain a sheet typically 4 to 8 mm thick.
  • the hot rolling exit temperature is below 300°C and preferably below 290°C.
  • the specific hot rolling conditions in combination with the composition according to the invention make it possible in particular to obtain a advantageous compromise between mechanical strength and toughness and low anisotropy of mechanical properties.
  • the sheet obtained can optionally be cold rolled, in particular to obtain a final thickness of between 0.5 and 3.9 mm.
  • the final thickness is at most 7.0 mm and more preferably at most 6.0 mm.
  • the final thickness is at least 0.8 mm and preferably at least 1.2 mm.
  • the sheet thus obtained is then dissolved between 450 and 515°C.
  • the dissolution time is advantageously between 5 min to 8 h.
  • the sheet thus placed in solution is then quenched.
  • the sheet then undergoes cold deformation by controlled traction with a permanent deformation of 0.5 to 6% and preferably of 3 to 5%.
  • Known steps such as rolling, planing, straightening and shaping can optionally be carried out after solution treatment and quenching and before or after controlled traction, however the total cold deformation after solution treatment and quenching must remain lower to 15% and preferably less than 10%.
  • High cold deformations after solution treatment and quenching in fact cause the appearance of numerous shear bands crossing several grains, these shear bands not being desirable.
  • no cold rolling is carried out after solution treatment.
  • Tempering is carried out comprising heating at a temperature of between 130 and 170° C. and preferably between 140 and 160° C. and preferably between 145 and 155° C. for 5 to 100 hours and preferably from 10 to 40 hours.
  • the final metallurgical state is a T8 state.
  • a short heat treatment is carried out after controlled traction and before tempering so as to improve the formability of the sheets.
  • the sheets can thus be shaped by a process such as stretch-forming before being tempered.
  • the thin sheets obtained by the process according to the invention have a characteristic grain size.
  • the average grain size in the thickness measured by the method of intercepts on an L/TC cut in the L direction according to the ASTM E112 standard and expressed in ⁇ m is less than 66 t + 200 where t is the thickness of the sheet expressed in mm, preferably less than 66 t + 150 and preferably less than 66 t + 100, for the thin sheets obtained by the process according to the invention.
  • the grain structure of the sheets is advantageously essentially recrystallized.
  • the thin sheets obtained by the process according to the invention have a particularly advantageous toughness in the TL direction.
  • the sheets according to the invention also exhibit low anisotropy.
  • the ratio between the elastic limit difference between the L and TL directions and the elastic limit in the L direction is less than 6% and preferably less than 5%.
  • the resistance to intergranular corrosion of the sheets according to the invention is high.
  • the sheet of the invention can be used without plating.
  • thin sheets according to the invention in a fuselage panel for an aircraft is advantageous.
  • the thin sheets according to the invention are also advantageous in aerospace applications such as the manufacture of rockets.
  • the plates were transformed according to the parameters indicated in table 2.
  • the transformation conditions used for the sheets of alloy A-1, A-2, B-1 and B-2 are in accordance with the invention.
  • the income requirements have been set to obtain a T8 state.
  • Table 2 Plate processing parameters Sheet metal A-1 A-2 B-1 B-2 C-1 C-2 D-1 D-2 Composition HAS HAS B B VS VS D D Homogenization 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C Hot rolling inlet temperature (°C) 434 430 430 432 452 451 447 448 Hot rolling outlet temperature (°C) 250 280 269 273 313 338 309 320 cold rolling Nope Nope Yes Nope Yes Nope Yes Nope Final thickness (mm) 6.4 4.0 1.6 4.0 3.2 6.4 2.2 4.0 Dissolution 40
  • Table 5 summarizes the toughness test results for these samples. Table 5 results of the R curves for the specimens with a width of 760 mm. Sheet metal K R app [MPa ⁇ m] KR60 [MPa ⁇ m] ⁇ a eff max valid [mm] TL LT TL LT TL LT A-1 135 161 181 213 82 108 A-2 140 168 187 222 134 85 B-1 135 154 178 206 103 109 B-2 135 163 180 216 148 84 C-1 126 155 167 208 140 120 C-2 110 157 142 208 83 100 D-1 124 152 162 201 187 128 D-2 126 158 166 131 97

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Description

Domaine de l'inventionField of invention

L'invention concerne les produits laminés alliages aluminium-cuivre-lithium, plus particulièrement, de tels produits, leurs procédés de fabrication et d'utilisation, destinés notamment à la construction aéronautique et aérospatiale.The invention relates to rolled aluminum-copper-lithium alloy products, more particularly, such products, their methods of manufacture and use, intended in particular for aeronautical and aerospace construction.

Etat de la techniqueState of the art

Des produits laminés en alliage d'aluminium sont développés pour produire des éléments de fuselage destinés notamment à l'industrie aéronautique et à l'industrie aérospatiale.Rolled aluminum alloy products are developed to produce fuselage components intended in particular for the aeronautical and aerospace industries.

Les alliages aluminium - cuivre - lithium sont particulièrement prometteurs pour fabriquer ce type de produit.Aluminum-copper-lithium alloys are particularly promising for manufacturing this type of product.

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 pour cent 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 5,455,003 décrit un procédé de fabrication d'alliages Al-Cu-Li qui présentent une résistance mécanique et une ténacité améliorées à température cryogénique, en particulier grâce à un écrouissage et un revenu appropriés. Ce brevet enseigne en particulier la composition, en pourcentage en poids, Cu = 2,0 - 6,5, Li = 0,2 - 2,7, Ag = 0 - 4,0, Mg = 0-4,0 et Zn = 0 - 3,0.The patent US 5,455,003 describes a process for the manufacture of Al-Cu-Li alloys which exhibit improved mechanical strength and toughness at cryogenic temperature, in particular thanks to suitable work hardening and tempering. This patent teaches in particular the composition, in percentage by weight, Cu = 2.0 - 6.5, Li = 0.2 - 2.7, Ag = 0 - 4.0, Mg = 0-4.0 and Zn = 0 - 3.0.

Le brevet EP0584271 décrit un alliage à base d'aluminium utile dans des structures aéronautiques et aérospatiales, possédant une faible densité, une résistance élevée et une forte ténacité à la rupture, correspondant essentiellement à la formule CuaLibMgcAgdZreAlba1 dans laquelle a, b, c, d, e et bal indiquent le pourcentage en poids des composants d'alliage, lesdits pourcentages étant 2,4 < a < 3,5, 1,35 < b < 1,8, 0,25 < c < 0,65, 0,25 < d < 0,65 et 0,08 < e < 0,25.The patent EP0584271 discloses an aluminum-based alloy useful in aircraft and aerospace structures, having low density, high strength and high fracture toughness, essentially corresponding to the formula CuaLibMgcAgdZreAlba1 in which a, b, c, d, e and bal indicate the percentage by weight of the alloying components, said percentages being 2.4 < a < 3.5, 1 .35 < b < 1.8, 0.25 < c < 0.65, 0.25 < d < 0.65 and 0.08 < e < 0.25.

Le brevet US 7,438,772 décrit des alliages comprenant, en pourcentage en poids, Cu : 3-5, Mg: 0,5-2, Li : 0,01-0,9 et décourage l'utilisation de teneurs en lithium plus élevées en raison d'une dégradation du compromis entre ténacité et résistance mécanique.The patent US 7,438,772 describes alloys comprising, in weight percent, Cu: 3-5, Mg: 0.5-2, Li: 0.01-0.9 and discourages the use of higher lithium contents due to degradation compromise between toughness and 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.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 refiners such as Cr, Ti, Hf, Sc, V.

La demande de brevet US 2011/0247730 décrit des alliages comprenant (en % en poids), 2.75 à 5.0% de Cu, 0,1 à 1,1 % de Li, 0,3 à 2.0 % de Ag, 0,2 à 0,8% de Mg, 0,50 à 1.5 % de Zn, jusque 1.0% de Mn, avec un rapport Cu/Mg compris entre 6,1 et 17, cet alliage étant peu sensible au corroyage.The patent application US 2011/0247730 describes alloys comprising (in % by weight), 2.75 to 5.0% Cu, 0.1 to 1.1% Li, 0.3 to 2.0% Ag, 0.2 to 0.8% Mg, 0 .50 to 1.5% Zn, up to 1.0% Mn, with a Cu/Mg ratio between 6.1 and 17, this alloy being insensitive to working.

La demande de brevet CN101967588 décrit des alliages de composition (en % en poids) Cu 2,8 - 4,0 ; Li 0,8 - 1,9 ; Mn 0,2-0,6 ; Zn 0,20 - 0,80, Zr 0,04 - 0,20, Mg 0,20 - 0,80, Ag 0,1 - 0,7, Si ≤ 0.10, Fe ≤ 0.10, Ti ≤ 0.12.The patent application CN101967588 describes alloys of composition (in % by weight) Cu 2.8 - 4.0; Li 0.8 - 1.9; Mn 0.2-0.6; Zn 0.20 - 0.80, Zr 0.04 - 0.20, Mg 0.20 - 0.80, Ag 0.1 - 0.7, Si ≤ 0.10, Fe ≤ 0.10, Ti ≤ 0.12.

Le brevet FR3014448 décrit un produit laminé et/ou forgé dont l'épaisseur est comprise entre 14 et 100 mm, en alliage d'aluminium de composition, en % en poids, Cu : 1,8 - 2,6 Li: 1,3 - 1,8 Mg : 0,1 - 0,5 Mn : 0,1 - 0,5 et Zr < 0,05 ou Mn < 0,05 et Zr 0.10 - 0.16 10 Ag : 0 - 0,5 Zn < 0,20 Ti : 0,01 - 0,15 Fe : < 0,1 Si : < 0,1 15 autres éléments < 0,05 chacun et < 0,15 au total, reste aluminium dont la densité est inférieure à 2,670 g/cm3 caractérisé en ce que à mi-épaisseur la fraction volumique des grains ayant une texture laiton est comprise entre 25 et 40 % et l'indice de texture est compris entre 12 et 18.The patent FR3014448 describes a rolled and/or forged product whose thickness is between 14 and 100 mm, in aluminum alloy of composition, in% by weight, Cu: 1.8 - 2.6 Li: 1.3 - 1, 8 Mg: 0.1 - 0.5 Mn: 0.1 - 0.5 and Zr < 0.05 or Mn < 0.05 and Zr 0.10 - 0.16 10 Ag: 0 - 0.5 Zn < 0.20 Ti : 0.01 - 0.15 Fe: < 0.1 Si: < 0.1 15 other elements < 0.05 each and < 0.15 in total, rest aluminum whose density is less than 2.670 g/cm3 characterized in that at mid-thickness the volume fraction of the grains having a brass texture is between 25 and 40% and the texture index is between 12 and 18.

La demande de brevet US2009084474 décrit un alliage d'aluminium recristallisé ayant une texture de laiton et une texture Goss, où la quantité de texture de laiton dépasse la quantité de texture de Goss et où l'alliage d'aluminium recristallisé présente au moins environ la même limite d'élasticité et la même résistance à la rupture qu'un alliage non -recristallisé même forme de produit et d'épaisseur et de trempe similaires.The patent application US2009084474 discloses a recrystallized aluminum alloy having a brass texture and a goss texture, where the amount of brass texture exceeds the amount of goss texture and where the recrystallized aluminum alloy has at least about the same yield strength and the same fracture toughness as an un-recrystallized alloy of the same product shape and similar thickness and temper.

Les caractéristiques nécessaires pour les tôles d'aluminium destinées aux applications de fuselage sont notamment décrites par exemple dans le brevet EP 1 891 247 . Il est souhaitable notamment que la tôle ait une limite d'élasticité élevée (pour résister au flambage) ainsi qu'une ténacité sous contrainte plane élevée, caractérisée notamment par une valeur élevée de facteur d'intensité de contrainte apparent à la rupture (Kapp) et une longue courbe R.The characteristics necessary for aluminum sheets intended for fuselage applications are in particular described, for example, in the patent EP 1 891 247 . It is particularly desirable for the sheet to have a high elastic limit (to resist buckling) as well as a toughness under high plane stress, characterized in particular by a high value of the stress intensity factor apparent at rupture (K app ) and a long R curve.

Le brevet EP 1 966 402 décrit un alliage comprenant 2,1 à 2,8 % en poids de Cu, 1,1 à 1,7 % en poids de Li, 0,1 à 0,8 % en poids de Ag, 0,2 à 0,6 % en poids de Mg, 0,2 à 0,6 % en poids de Mn, une quantité de Fe et de Si inférieure ou égale à 0,1 % en poids chacun, et des impuretés inévitables à une teneur inférieure ou égale à 0,05% en poids chacune et 0,15% en poids au total, l'alliage étant sensiblement exempt de zirconium, particulièrement adapté pour l'obtention de tôles minces recristallisées.
Pour certaines applications de fuselage, il est particulièrement important que la ténacité soit élevée dans la direction T-L. En effet, une grande partie du fuselage est dimensionnée pour résister à la pression interne de l'avion. La direction longitudinale des tôles étant en général positionnée dans la direction de la longueur de l'avion, celles-ci sont contrainte dans la direction transverse par la pression. Les fissures sont alors sollicitées dans la direction T-L. Il peut être également avantageux que les tôles présentent une faible anisotropie de propriétés mécaniques, notamment entre les directions L et TL.The patent EP 1 966 402 describes an alloy comprising 2.1 to 2.8 wt% Cu, 1.1 to 1.7 wt% Li, 0.1 to 0.8 wt% Ag, 0.2 to 0.6 % by weight of Mg, 0.2 to 0.6% by weight of Mn, an amount of Fe and Si less than or equal to 0.1% by weight each, and unavoidable impurities at a content less than or equal to 0 0.05% by weight each and 0.15% by weight in total, the alloy being substantially free of zirconium, particularly suitable for obtaining recrystallized thin sheets.
For some fuselage applications, it is particularly important that the toughness be high in the TL direction. Indeed, a large part of the fuselage is dimensioned to resist the internal pressure of the aircraft. The longitudinal direction of the sheets being generally positioned in the direction of the length of the aircraft, these are constrained in the transverse direction by the pressure. The cracks are then stressed in the direction TL. It may also be advantageous for the sheets to have low anisotropy of mechanical properties, in particular between the L and TL directions.

Il est connu du brevet EP 1 891 247 que pour les tôles dont l'épaisseur est comprise entre 4 et 12 mm, il peut être avantageux que la microstructure soit complètement non-recristallisée. Cependant l'effet de la structure granulaire sur les propriétés peut être différent à différentes épaisseurs.It is known from the patent EP 1 891 247 that for sheets whose thickness is between 4 and 12 mm, it may be advantageous for the microstructure to be completely non-recrystallized. However the effect of the grain structure on the properties may be different at different thicknesses.

Il existe un besoin pour des tôles minces, d'épaisseur 0,5 à 8 mm, en alliage aluminium-cuivre-lithium présentant des propriétés améliorées par rapport à celles des produits connus, en particulier en termes de ténacité dans la direction T-L, de propriétés de résistance mécanique statique et de résistance à la corrosion, tout en ayant une faible densité et une faible anisotropie des propriétés mécaniques. Par ailleurs il existe un besoin pour un procédé simple et économique d'obtention de ces tôles minces.There is a need for thin sheets, with a thickness of 0.5 to 8 mm, in aluminium-copper-lithium alloy having improved properties compared to those of known products, in particular in terms of toughness in the T-L direction, of properties of static mechanical strength and corrosion resistance, while having low density and low anisotropy of mechanical properties. Furthermore, there is a need for a simple and economical process for obtaining these thin sheets.

Objet de l'inventionObject of the invention

Un objet de l'invention est un procédé de fabrication d'une tôle mince d'épaisseur 0,5 à 8 mm en alliage à base d'aluminium dans lequel, successivement

  1. a) on élabore un bain de métal liquide comprenant
    • 2,3 à 2,7 % en poids de Cu,
    • 1,3 à 1,6 % en poids de Li,
    • 0,2 à 0,5 % en poids de Mg,
    • 0,1 à 0,5 % en poids de Mn,
    • 0,01 à 0,15 % en poids de Ti,
    une quantité de Zn inférieure à 0,3 % en poids, une quantité de Fe et de Si inférieure ou égale à 0,1 % en poids chacun, et des impuretés inévitables à une teneur inférieure ou égale à 0,05% en poids chacune et 0,15% en poids au total,
  2. b) on coule une plaque à partir dudit bain de métal liquide ;
  3. c) on homogénéise ladite plaque à une température comprise entre 490°C et 535°C;
  4. d) on lamine ladite plaque par laminage à chaud et optionnellement par laminage à froid en une tôle ayant une épaisseur comprise entre 0,5 et 8 mm, la température d'entrée de laminage à chaud étant comprise entre 400°C et 445°C et la température de sortie de laminage à chaud étant inférieure à 300°C;
  5. e) on met en solution à une température comprise entre 450°C et 515 °C et on trempe ladite tôle ;
  6. f) on tractionne de façon contrôlée ladite tôle avec une déformation permanente de 0,5 à 6 %, la déformation à froid après mise en solution étant inférieure à 15% ;
  7. g) on effectue un revenu comprenant un chauffage à une température comprise entre 130 et 170°C et de préférence entre 150 et 160°C pendant 5 à 100 heures et de préférence de 10 à 40h.
An object of the invention is a process for manufacturing a thin sheet 0.5 to 8 mm thick in aluminum-based alloy in which, successively
  1. a) a liquid metal bath comprising
    • 2.3 to 2.7% by weight of Cu,
    • 1.3 to 1.6% by weight of Li,
    • 0.2 to 0.5% by weight of Mg,
    • 0.1 to 0.5% by weight of Mn,
    • 0.01 to 0.15% by weight of Ti,
    an amount of Zn less than 0.3% by weight, an amount of Fe and Si less than or equal to 0.1% by weight each, and unavoidable impurities at a content less than or equal to 0.05% by weight each and 0.15% by weight in total,
  2. b) casting a plate from said liquid metal bath;
  3. c) said plate is homogenized at a temperature between 490°C and 535°C;
  4. d) said plate is rolled by hot rolling and optionally by cold rolling into a sheet having a thickness of between 0.5 and 8 mm, the hot rolling entry temperature being between 400°C and 445°C and the hot rolling exit temperature being less than 300°C;
  5. e) solution is placed at a temperature between 450° C. and 515° C. and said sheet is quenched;
  6. f) the said sheet is pulled in a controlled manner with a permanent deformation of 0.5 to 6%, the cold deformation after solution treatment being less than 15%;
  7. g) tempering is carried out comprising heating at a temperature of between 130 and 170° C. and preferably between 150 and 160° C. for 5 to 100 hours and preferably from 10 to 40 hours.

Un autre objet de l'invention est une tôle obtenue par le procédé selon l'invention dont la taille de grain moyenne dans l'épaisseur mesurée par la méthode des intercepts sur une coupe L/TC dans la direction L selon la norme ASTM E112 et exprimée en µm est inférieure à 66 t + 200 où t est l'épaisseur de la tôle exprimée en mm.Another object of the invention is a sheet obtained by the process according to the invention, the average grain size of which in the thickness measured by the method of intercepts on an L/TC section in the direction L according to the standard ASTM E112 and expressed in µm is less than 66 t + 200 where t is the thickness of the sheet expressed in mm.

Encore un autre objet de l'invention est l'utilisation d'une tôle mince selon l'invention dans un panneau de fuselage pour aéronef.Yet another object of the invention is the use of a thin sheet according to the invention in a fuselage panel for an aircraft.

Description des figuresDescription of figures

  • Figure 1 : Coupe métallographique de la tôle A-1. Figure 1 : Metallographic section of sheet A-1.
  • Figure 2: Coupe métallographique de la tôle C-2. Figure 2 : Metallographic section of sheet C-2.
  • Figure 3 : Relation entre la limite d'élasticité dans le sens TL et le facteur d'intensité de contrainte KR60 T-L mesuré sur des échantillons de largeur 760 mm pour les tôles de l'exemple 1. Figure 3 : Relationship between the elastic limit in the direction TL and the stress intensity factor KR60 TL measured on samples 760 mm wide for the plates of example 1.
Description de l'inventionDescription 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. La densité dépend de la composition et est déterminée par calcul plutôt que par une méthode de mesure de poids. Les valeurs sont calculées en conformité avec la procédure de The Aluminium Association, qui est décrite pages 2-12 et 2-13 de « Aluminum Standards and Data » . Sauf mention contraire les définitions des états métallurgiques indiquées dans la norme européenne EN 515 (1993) s'appliquent.Unless otherwise stated, all indications regarding the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy. The expression 1.4 Cu means that the copper content expressed in % by weight is multiplied by 1.4. The designation of the alloys is made in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The density depends on the composition and is determined by calculation rather than by a method of measuring weight. 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” . Unless otherwise stated otherwise the definitions of metallurgical tempers given in European standard EN 515 (1993) apply.

Les caractéristiques mécaniques statiques en traction, 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 déterminés par un essai de traction selon la norme NF EN ISO 6892-1 (2016), le prélèvement et le sens de l'essai étant définis par la norme EN 485-1 (2016).The static mechanical characteristics in tension, in other words the breaking 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 NF EN ISO 6892-1 (2016), the sampling and direction of the test being defined by standard EN 485-1 (2016).

Dans le cadre de l'invention, les caractéristiques mécaniques sont mesurées en pleine épaisseur.In the context of the invention, the mechanical characteristics are measured at full thickness.

Une courbe donnant le facteur d'intensité de contrainte effectif en fonction de l'extension de fissure effective, connue comme la courbe R, est déterminée selon la norme ASTM E 561. Le facteur d'intensité de contrainte critique Kc, en d'autres termes le facteur d'intensité qui rend la fissure instable, est calculé à partir de la courbe R. Le facteur d'intensité de contrainte KCO est également calculé en attribuant la longueur de fissure initiale au commencement de la charge monotone, à la charge critique. Ces deux valeurs sont calculées pour une éprouvette de la forme requise. Kapp représente le facteur KCO correspondant à l'éprouvette qui a été utilisée pour effectuer l'essai de courbe R. Keff représente le facteur Kc correspondant à l'éprouvette qui a été utilisée pour effectuer l'essai de courbe R. KR60 représente le facteur d'intensité de contrainte correspondant à l'extension de fissure Δaeff = 60 mm. Δaeff(max) représente l'extension de fissure du dernier point de la courbe R, valide selon la norme ASTM E561. Le dernier point est obtenu soit au moment de la rupture brutale de l'éprouvette, soit éventuellement au moment où la contrainte sur le ligament non fissuré excède en moyenne la limite d'élasticité du matériau. Sauf mention contraire, la taille de fissure à la fin du stade de pré-fissurage par fatigue est W/3 pour des éprouvettes du type M(T), dans laquelle W est la largeur de l'éprouvette telle que définie dans la norme ASTM E561 (ASTM E561-10-2).A curve giving the effective stress intensity factor as a function of the effective crack extension, known as the R-curve, is determined according to ASTM E 561. The critical stress intensity factor Kc, in other terms the intensity factor which makes the crack unstable, is calculated from the R curve. The stress intensity factor K CO is also calculated by assigning the initial crack length at the beginning of the monotonic load, to the load critical. These two values are calculated for a specimen of the required shape. K app represents the K CO factor corresponding to the specimen that was used to perform the R curve test. K eff represents the Kc factor corresponding to the specimen that was used to perform the R curve test. K R60 represents the stress intensity factor corresponding to the crack extension Δa eff = 60 mm. Δa eff (max) represents the crack extension of the last point of the R-curve, valid according to ASTM E561. The last point is obtained either at the moment of the sudden rupture of the specimen, or possibly at the moment when the stress on the uncracked ligament exceeds on average the elastic limit of the material. Unless otherwise stated, the crack size at the end of the pre-fatigue cracking stage is W/3 for type M(T) specimens, where W is the width of the specimen as defined in the ASTM standard E561 (ASTM E561-10-2).

Sauf mention contraire, les définitions de la norme EN 12258 (2012) s'appliquent.Unless otherwise stated, the definitions of EN 12258 (2012) apply.

Dans le cadre de la présente invention, on appelle structure granulaire essentiellement recristallisée une structure granulaire telle que le taux de recristallisation à ½ épaisseur est supérieur à 70% et de préférence supérieur à 90%. Le taux de recristallisation est défini comme la fraction de surface sur une coupe métallographique occupée par des grains recristallisés.In the context of the present invention, an essentially recrystallized granular structure is a granular structure such that the rate of recrystallization at ½ thickness is greater than 70% and preferably greater than 90%. The recrystallization rate is defined as the fraction of area on a metallographic section occupied by recrystallized grains.

Les présents inventeurs ont obtenus des tôles d'épaisseur 0,5 à 8 mm présentant un compromis avantageux entre la résistance mécanique et la ténacité en utilisant le procédé selon l'invention qui comprend notamment la combinaison de

  • une sélection étroite de la composition,
  • une déformation par laminage à chaud dans des conditions rigoureusement contrôlées.
The present inventors have obtained sheets with a thickness of 0.5 to 8 mm having an advantageous compromise between mechanical strength and toughness by using the method according to the invention which comprises in particular the combination of
  • a narrow selection of the composition,
  • deformation by hot rolling under rigorously controlled conditions.

Les tôles minces ainsi obtenues ont des propriétés particulièrement avantageuses, notamment en ce qui concerne la ténacité dans la direction T-L et l'anisotropie des propriétés mécaniques.The thin sheets thus obtained have particularly advantageous properties, in particular as regards the toughness in the T-L direction and the anisotropy of the mechanical properties.

Dans le procédé selon l'invention, on élabore un bain de métal liquide dont la composition est la suivante :

  • 2,3 à 2,7 % en poids de Cu,
  • 1,3 à 1,6 % en poids de Li,
  • 0,2 à 0,5 % en poids de Mg,
  • 0,1 à 0,5 % en poids de Mn,
  • 0,01 à 0,15 % en poids de Ti,
In the process according to the invention, a bath of liquid metal is produced, the composition of which is as follows:
  • 2.3 to 2.7% by weight of Cu,
  • 1.3 to 1.6% by weight of Li,
  • 0.2 to 0.5% by weight of Mg,
  • 0.1 to 0.5% by weight of Mn,
  • 0.01 to 0.15% by weight of Ti,

une quantité de Zn inférieure à 0,3 % en poids, une quantité de Fe et de Si inférieure ou égale à 0,1 % en poids chacun, et des impuretés inévitables à une teneur inférieure ou égale à 0,05% en poids chacune et 0,15% en poids au total,an amount of Zn less than 0.3% by weight, an amount of Fe and Si less than or equal to 0.1% by weight each, and unavoidable impurities at a content less than or equal to 0.05% by weight each and 0.15% by weight in total,

La teneur en cuivre des produits selon l'invention est comprise entre 2,3 et 2,7 % en poids. Dans un mode de réalisation avantageux de l'invention la teneur en cuivre est au moins de 2,4 % en poids, de préférence au moins 2,45% en poids et préférentiellement au moins 2,50% en poids. Dans une réalisation avantageuse de l'invention, la teneur en cuivre est comprise entre 2,45 et 2,65 % en poids et de préférence entre 2,50 et 2,60 % en poids. Dans un mode de réalisation avantageux de l'invention la teneur en cuivre est au plus de 2,65 % en poids et préférentiellement au plus 2,60% en poids. Dans un mode de réalisation de l'invention la teneur en cuivre est au plus de 2,53 % en poids. Lorsque la teneur en cuivre est trop élevée, une valeur très élevée de ténacité dans la direction T-L peut ne pas être atteinte. Lorsque la teneur en cuivre est trop faible, les caractéristiques mécaniques statiques minimales ne sont pas atteintes.The copper content of the products according to the invention is between 2.3 and 2.7% by weight. In an advantageous embodiment of the invention, the copper content is at least 2.4% by weight, preferably at least 2.45% by weight and preferably at least 2.50% by weight. In an advantageous embodiment of the invention, the copper content is between 2.45 and 2.65% by weight and preferably between 2.50 and 2.60% by weight. In an advantageous embodiment of the invention the copper content is at most 2.65% by weight and preferably at most 2.60% by weight. In one embodiment of the invention the copper content is at most 2.53% by weight. When the copper content is too high, a very high value of toughness in the TL direction may not be achieved. When the copper content is too low, the minimum static mechanical characteristics are not achieved.

La teneur en lithium des produits selon l'invention est comprise entre 1,3 et 1.6 % en poids. Avantageusement, la teneur en lithium est comprise entre 1,35 et 1,55 % en poids et de préférence entre 1,40 % et 1,50 % en poids. Une teneur minimale de lithium de 1,35 % en poids et de préférence 1,40 % en poids est avantageuse. Une teneur maximale de lithium de 1,55 % en poids et de préférence 1,50 % en poids est avantageuse, notamment pour améliorer le compromis entre ténacité et résistance mécanique. L'addition de lithium peut contribuer à l'augmentation de la résistance mécanique et de la ténacité, une teneur trop élevée ou trop faible ne permet pas d'obtenir une valeur très élevée de ténacité dans la direction T-L et/ou une limite d'élasticité suffisante. Par ailleurs l'addition de lithium permet de diminuer la densité. Avantageusement la densité des produits selon l'invention est inférieure à 2,65.The lithium content of the products according to the invention is between 1.3 and 1.6% by weight. Advantageously, the lithium content is between 1.35 and 1.55% by weight and preferably between 1.40% and 1.50% by weight. A minimum lithium content of 1.35% by weight and preferably 1.40% by weight is advantageous. A maximum lithium content of 1.55% by weight and preferably 1.50% by weight is advantageous, in particular to improve the compromise between toughness and mechanical strength. The addition of lithium can contribute to the increase in mechanical strength and toughness, too high or too low a content does not make it possible to obtain a very high value of toughness in the T-L direction and/or a limit of sufficient elasticity. Moreover, the addition of lithium makes it possible to reduce the density. Advantageously, the density of the products according to the invention is less than 2.65.

La teneur en magnésium des produits selon l'invention est comprise entre 0,2 et 0,5 % en poids et de manière préférée entre 0,25 et 0,45 % en poids et de préférence entre 0,25 et 0,35 % en poids. Une teneur minimale de magnésium de 0,25 % en poids est avantageuse. Une teneur maximale de magnésium de 0,45 % en poids et de préférence 0,40 % en poids et préférentiellement 0,35 % en poids ou même 0,30 % en poids est avantageuse.The magnesium content of the products according to the invention is between 0.2 and 0.5% by weight and preferably between 0.25 and 0.45% by weight and preferably between 0.25 and 0.35% in weight. A minimum magnesium content of 0.25% by weight is advantageous. A maximum magnesium content of 0.45% by weight and preferably 0.40% by weight and preferably 0.35% by weight or even 0.30% by weight is advantageous.

La teneur en manganèse est comprise entre 0,1 et 0,5 % en poids, de préférence entre 0,2 et 0,4% en poids et préférentiellement entre 0,25 et 0,35 % en poids. Une teneur minimale de manganèse de 0,2 % en poids et de préférence 0,25 % en poids est avantageuse. Une teneur maximale de manganèse de 0,4 % en poids et de préférence 0,35 % en poids ou même de 0,33 % en poids est avantageuse.The manganese content is between 0.1 and 0.5% by weight, preferably between 0.2 and 0.4% by weight and preferably between 0.25 and 0.35% by weight. A minimum manganese content of 0.2% by weight and preferably 0.25% by weight is advantageous. A maximum manganese content of 0.4% by weight and preferably 0.35% by weight or even 0.33% by weight is advantageous.

La teneur en titane est comprise entre 0,01 et 0,15 % en poids. L'addition de titane, éventuellement combiné avec du bore et/ou du carbone, contribue à contrôler la structure granulaire, notamment lors de la coulée.The titanium content is between 0.01 and 0.15% by weight. The addition of titanium, optionally combined with boron and/or carbon, contributes to controlling the granular structure, in particular during casting.

De préférence, les teneurs en fer et en silicium sont chacune au plus de 0,1 % en poids. Dans une réalisation avantageuse de l'invention les teneurs en fer et en silicium sont au plus de 0,08 % et préférentiellement au plus de 0,04 % en poids. Une teneur en fer et en silicium contrôlée et limitée contribue à l'amélioration du compromis entre résistance mécanique et tolérance aux dommages.Preferably, the iron and silicon contents are each at most 0.1% by weight. In an advantageous embodiment of the invention, the iron and silicon contents are at most 0.08% and preferably at most 0.04% by weight. A controlled and limited iron and silicon content contributes to the improvement of the compromise between mechanical resistance and damage tolerance.

La teneur en zinc est inférieure à 0,3 % en poids, préférentiellement inférieure à 0,2 % en poids et de préférence inférieure à 0,1 % en poids. La teneur en zinc est avantageusement inférieure à 0,04 % en poids.The zinc content is less than 0.3% by weight, preferably less than 0.2% by weight and preferably less than 0.1% by weight. The zinc content is advantageously less than 0.04% by weight.

Les impuretés inévitables sont maintenues à une teneur inférieure ou égale à 0,05% en poids chacune et 0,15% en poids au total.The unavoidable impurities are maintained at a content less than or equal to 0.05% by weight each and 0.15% by weight in total.

Le procédé de fabrication des tôles minces selon l'invention comprend ensuite des étapes de coulée, homogénéisation, laminage à chaud et optionnellement à froid, mise en solution, traction contrôlée, trempe et revenu.The process for manufacturing thin sheets according to the invention then comprises steps of casting, homogenization, hot and optionally cold rolling, solution treatment, controlled traction, quenching and tempering.

Le bain de métal liquide élaboré est coulé sous une forme de plaque de laminage.The formed liquid metal bath is cast in a rolling plate form.

La plaque de laminage est ensuite homogénéisée à une température comprise entre 490°C et 535°C. De préférence, la durée d'homogénéisation est comprise entre 5 et 60 heures. Avantageusement, la température d'homogénéisation est au moins 500 °C. Dans un mode de réalisation, la température d'homogénéisation est inférieure à 515 °C.The rolling plate is then homogenized at a temperature between 490°C and 535°C. Preferably, the homogenization time is between 5 and 60 hours. Advantageously, the homogenization temperature is at least 500°C. In one embodiment, the homogenization temperature is less than 515°C.

Après homogénéisation, la plaque de laminage est en général refroidie jusqu'à température ambiante avant d'être préchauffée en vue d'être déformée à chaud. Le préchauffage a pour objectif d'atteindre une température d'entrée de laminage à chaud comprise entre 400 et 445 °C et de préférence comprise entre 420°C et 440°C permettant la déformation par laminage à chaud.After homogenization, the rolling plate is generally cooled to ambient temperature before being preheated in order to be hot deformed. The purpose of the preheating is to reach a hot rolling inlet temperature of between 400 and 445° C. and preferably of between 420° C. and 440° C. allowing the deformation by hot rolling.

Le laminage à chaud est effectué de manière à obtenir une tôle d'épaisseur typiquement 4 à 8 mm. La température de sortie de laminage à chaud est inférieure à 300 °C et de préférence inférieure à 290 °C. Les conditions spécifiques de laminage à chaud en combinaison avec la composition selon l'invention permettent notamment d'obtenir un compromis avantageux entre la résistance mécanique et la ténacité et une faible anisotropie des propriétés mécaniques.The hot rolling is carried out so as to obtain a sheet typically 4 to 8 mm thick. The hot rolling exit temperature is below 300°C and preferably below 290°C. The specific hot rolling conditions in combination with the composition according to the invention make it possible in particular to obtain a advantageous compromise between mechanical strength and toughness and low anisotropy of mechanical properties.

Après laminage à chaud, on peut optionnellement laminer à froid la tôle obtenue notamment pour obtenir une épaisseur finale comprise entre 0,5 et 3,9 mm. Préférentiellement, l'épaisseur finale est au plus de 7,0 mm et de manière préférée au plus de 6,0 mm. Avantageusement l'épaisseur finale est au moins de 0,8 mm et de manière préférée au moins de 1,2 mm.After hot rolling, the sheet obtained can optionally be cold rolled, in particular to obtain a final thickness of between 0.5 and 3.9 mm. Preferably, the final thickness is at most 7.0 mm and more preferably at most 6.0 mm. Advantageously, the final thickness is at least 0.8 mm and preferably at least 1.2 mm.

La tôle ainsi obtenue est ensuite mise en solution entre 450 et 515 °C. La durée de mise en solution est avantageusement comprise entre 5 min à 8 h. La tôle ainsi mise en solution est ensuite trempée.The sheet thus obtained is then dissolved between 450 and 515°C. The dissolution time is advantageously between 5 min to 8 h. The sheet thus placed in solution is then quenched.

Il est connu de l'homme du métier que les conditions précises de mise en solution doivent être choisies en fonction de l'épaisseur et de la composition de façon à mettre en solution solide les éléments durcissants.It is known to those skilled in the art that the precise conditions for dissolving must be chosen according to the thickness and the composition so as to put the hardening elements in solid solution.

La tôle subit ensuite une déformation à froid par traction contrôlée avec une déformation permanente de 0,5 à 6 % et préférentiellement de 3 à 5%. Des étapes connues telles que le laminage, le planage, le redressage la mise en forme peuvent être optionnellement réalisées après mise en solution et trempe et avant ou après la traction contrôlée, cependant la déformation à froid totale après mise en solution et trempe doit rester inférieure à 15% et de préférence inférieure à 10%. Des déformations à froid élevées après mise en solution et trempe causent en effet l'apparition de nombreuses bandes de cisaillement traversant plusieurs grains, ces bandes de cisaillement n'étant pas souhaitables. De préférence on ne réalise pas de laminage à froid après la mise en solution.The sheet then undergoes cold deformation by controlled traction with a permanent deformation of 0.5 to 6% and preferably of 3 to 5%. Known steps such as rolling, planing, straightening and shaping can optionally be carried out after solution treatment and quenching and before or after controlled traction, however the total cold deformation after solution treatment and quenching must remain lower to 15% and preferably less than 10%. High cold deformations after solution treatment and quenching in fact cause the appearance of numerous shear bands crossing several grains, these shear bands not being desirable. Preferably, no cold rolling is carried out after solution treatment.

Un revenu est réalisé comprenant un chauffage à une température comprise entre 130 et 170°C et de préférence entre 140 et 160°C et de manière préférée entre 145 et 155 °C pendant 5 à 100 heures et de préférence de 10 à 40h. De manière préférée, l'état métallurgique final est un état T8.Tempering is carried out comprising heating at a temperature of between 130 and 170° C. and preferably between 140 and 160° C. and preferably between 145 and 155° C. for 5 to 100 hours and preferably from 10 to 40 hours. Preferably, the final metallurgical state is a T8 state.

Dan un mode de réalisation de l'invention, un traitement thermique court est réalisé après traction contrôlée et avant revenu de façon à améliorer la formabilité des tôles. Les tôles peuvent ainsi être mises en forme par un procédé tel que l'étirage-formage avant d'être revenues.In one embodiment of the invention, a short heat treatment is carried out after controlled traction and before tempering so as to improve the formability of the sheets. The sheets can thus be shaped by a process such as stretch-forming before being tempered.

Les tôles minces obtenues par le procédé selon l'invention ont une taille de grain caractéristique. Ainsi, la taille de grain moyenne dans l'épaisseur mesurée par la méthode des intercepts sur une coupe L/TC dans la direction L selon la norme ASTM E112 et exprimée en µm est inférieure à 66 t + 200 où t est l'épaisseur de la tôle exprimée en mm, de préférence inférieure à 66 t + 150 et de manière préférée inférieure à 66 t + 100, pour les tôles minces obtenues par le procédé selon l'invention. La structure granulaire des tôles est avantageusement essentiellement recristallisée.The thin sheets obtained by the process according to the invention have a characteristic grain size. Thus, the average grain size in the thickness measured by the method of intercepts on an L/TC cut in the L direction according to the ASTM E112 standard and expressed in µm is less than 66 t + 200 where t is the thickness of the sheet expressed in mm, preferably less than 66 t + 150 and preferably less than 66 t + 100, for the thin sheets obtained by the process according to the invention. The grain structure of the sheets is advantageously essentially recrystallized.

Les tôles minces obtenues par le procédé selon l'invention ont une ténacité dans la direction T-L particulièrement avantageuse. En particulier, les tôles minces obtenues par le procédé selon l'invention présentent avantageusement une limite d'élasticité Rp0,2 dans la direction TL d'au moins de 370 MPa, préférentiellement d'au moins 380 MPa et de manière préférée d'au moins 390 MPa, et une ténacité en contrainte plane KR60, mesurée sur des éprouvettes de type CCT760 (2ao = 253 mm), d'au moins 170 MPa√m, préférentiellement d'au moins 175 MPa√m et de manière préférée d'au moins 180 MPa√m. Les performances les plus favorables des tôles selon l'invention, notamment pour une épaisseur comprise entre 2 mm et 7 mm à savoir une limite d'élasticité Rp0,2 dans la direction TL d'au moins de 393 MPa, une ténacité en contrainte plane KR60, mesurée sur des éprouvettes de type CCT760 (2ao = 253 mm), dans la direction T-L d'au moins 180 MPa √m sont notamment obtenues lorsque la teneur en lithium est comprise entre 1,40 et 1,50 % en poids, la teneur en cuivre est comprise entre 2,45 et 2,55 % en poids et la teneur en magnésium est comprise entre 0,25 et 0,35 % en poids.The thin sheets obtained by the process according to the invention have a particularly advantageous toughness in the TL direction. In particular, the thin sheets obtained by the process according to the invention advantageously have an elastic limit R p0.2 in the direction TL of at least 370 MPa, preferentially of at least 380 MPa and preferably of at least 390 MPa, and a plane stress toughness K R60 , measured on CCT760 type specimens (2ao = 253 mm), of at least 170 MPa√m, preferentially of at least 175 MPa√m and preferably at least 180 MPa√m. The most favorable performances of the sheets according to the invention, in particular for a thickness of between 2 mm and 7 mm, namely an elastic limit R p0.2 in the direction TL of at least 393 MPa, a stress toughness plane K R60 , measured on CCT760 type specimens (2ao = 253 mm), in the TL direction of at least 180 MPa √m are obtained in particular when the lithium content is between 1.40 and 1.50% in weight, the copper content is between 2.45 and 2.55% by weight and the magnesium content is between 0.25 and 0.35% by weight.

Les tôles selon l'invention présentent également une faible anisotropie. Ainsi, le rapport entre la différence de limite d'élasticité entre les directions L et TL et la limite d'élasticité dans la direction L est inférieur à 6% et de préférence inférieur à 5%.The sheets according to the invention also exhibit low anisotropy. Thus, the ratio between the elastic limit difference between the L and TL directions and the elastic limit in the L direction is less than 6% and preferably less than 5%.

La résistance à la corrosion intergranulaire des tôles selon l'invention est élevée. Dans un mode de réalisation préféré de l'invention, la tôle de l'invention peut être utilisée sans placage.The resistance to intergranular corrosion of the sheets according to the invention is high. In a preferred embodiment of the invention, the sheet of the invention can be used without plating.

L'utilisation de tôles minces selon l'invention dans un panneau de fuselage pour aéronef est avantageuse. Les tôles minces selon l'invention sont également avantageuses dans les applications aérospatiales telles que la fabrication de fusées.The use of thin sheets according to the invention in a fuselage panel for an aircraft is advantageous. The thin sheets according to the invention are also advantageous in aerospace applications such as the manufacture of rockets.

ExempleExample

Dans cet exemple, 8 tôles minces ont été préparées.In this example, 8 thin sheets were prepared.

Des alliages dont la composition est donnée dans le Tableau 1 ont été coulés : Tableau 1- Composition (%en poids) Cu Li Mg Mn Ti Fe Si Zn A 2,51 1.43 0,28 0,30 0,03 0,04 0,03 < 0,01 B 2,56 1.54 0,26 0,30 0,04 0.04 0.03 < 0,01 C 2,52 1.46 0,35 0,36 0,04 0,04 0,03 < 0,01 D 2,59 1.46 0,34 0,36 0,04 0,04 0,02 < 0,01 Alloys whose composition is given in Table 1 were cast: Table 1- Composition (% by weight) Cu Li mg min You Fe Whether Zn HAS 2.51 1.43 0.28 0.30 0.03 0.04 0.03 < 0.01 B 2.56 1.54 0.26 0.30 0.04 0.04 0.03 < 0.01 VS 2.52 1.46 0.35 0.36 0.04 0.04 0.03 < 0.01 D 2.59 1.46 0.34 0.36 0.04 0.04 0.02 < 0.01

Les plaques ont été transformées selon les paramètres indiqués dans le tableau 2. Les conditions de transformation utilisées pour les tôles en alliage A-1, A-2, B-1 et B-2 sont conformes à l'invention. Les conditions de revenu ont été définies de façon à obtenir un état T8. Tableau 2. Paramètres de transformation des tôles Tôle A-1 A-2 B-1 B-2 C-1 C-2 D-1 D-2 Composition A A B B C C D D Homogénéisation 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C Température entrée laminage à chaud (°C) 434 430 430 432 452 451 447 448 Température sortie laminage à chaud (°C) 250 280 269 273 313 338 309 320 Laminage à froid Non Non Oui Non Oui Non Oui Non Epaisseur finale (mm) 6,4 4,0 1,6 4,0 3,2 6,4 2,2 4,0 Mise en solution 40min à 500°C 30min à 500°C 10min à 500°C 30min à 500°C 20min à 500°C 40min à 500°C 20min à 500°C 30min à 500°C Traction 4,1 à 4,5% 4.0 à 4.7% 4,5 à 4,9% 4.4 à 4.6% 4.2 à 4.6% 4.1 à 4.3% 3.8 à 4.6% 3.5 à 4.3% Revenu 34h à 155°C 34h à 155°C 34h à 155°C 34h à 155°C 28h à 155°C 28h à 155°C 28h à 155°C 28h à 155°C La structure granulaire des échantillons a été caractérisée à partir de l'observation microscopique des sections transversales après oxydation anodique, sous lumière polarisée sur des coupes L/TC. Les microstructures observées pour les échantillons A-1 et C-2 sont présentées sur les Figures 1 et 2, respectivement. La structure granulaire des tôles était essentiellement recristallisée. Les tailles de grain moyennes dans l'épaisseur mesurées par la méthode des intercepts selon la norme ASTM E112 sont présentées dans le Tableau 3. Tableau 3. Tailles de grain mesurées sur des coupes L/TC Tôle Taille de grain Aspect ratio L (µm) TC (µm) A-1 194 28 7 A-2 339 34 10 B-1 194 41 5 B-2 337 31 11 C-1 506 45 11 C-2 813 45 19 D-1 542 56 8 D-2 545 47 12 The plates were transformed according to the parameters indicated in table 2. The transformation conditions used for the sheets of alloy A-1, A-2, B-1 and B-2 are in accordance with the invention. The income requirements have been set to obtain a T8 state. Table 2. Plate processing parameters Sheet metal A-1 A-2 B-1 B-2 C-1 C-2 D-1 D-2 Composition HAS HAS B B VS VS D D Homogenization 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C 12h 505°C Hot rolling inlet temperature (°C) 434 430 430 432 452 451 447 448 Hot rolling outlet temperature (°C) 250 280 269 273 313 338 309 320 cold rolling Nope Nope Yes Nope Yes Nope Yes Nope Final thickness (mm) 6.4 4.0 1.6 4.0 3.2 6.4 2.2 4.0 Dissolution 40min at 500°C 30min at 500°C 10min at 500°C 30min at 500°C 20min at 500°C 40min at 500°C 20min at 500°C 30min at 500°C Traction 4.1 to 4.5% 4.0 to 4.7% 4.5 to 4.9% 4.4 to 4.6% 4.2 to 4.6% 4.1 to 4.3% 3.8 to 4.6% 3.5 to 4.3% Revenue 34h at 155°C 34h at 155°C 34h at 155°C 34h at 155°C 28h at 155°C 28h at 155°C 28h at 155°C 28h at 155°C The granular structure of the samples was characterized from the microscopic observation of the cross sections after anodic oxidation, under polarized light on L/TC sections. The microstructures observed for samples A-1 and C-2 are presented on the Figures 1 and 2 , respectively. The grain structure of the sheets was essentially recrystallized. The average grain sizes in the thickness measured by the intercept method according to the ASTM E112 standard are presented in Table 3. Sheet metal grain size aspect ratio L (µm) TC (µm) A-1 194 28 7 A-2 339 34 10 B-1 194 41 5 B-2 337 31 11 C-1 506 45 11 C-2 813 45 19 D-1 542 56 8 D-2 545 47 12

Les échantillons ont été testés mécaniquement afin de déterminer leurs propriétés mécaniques statiques ainsi que leur résistance à la propagation des fissures. La limite d'élasticité en traction, la résistance à la rupture et l'allongement à la rupture sont fournis dans le tableau 4. Tableau 4- Caractéristiques mécaniques exprimées en MPa (Rp0,2, Rm) ou en pourcentage (A%) Tôle Rp0,2 (L) Rm(L) A%(L) Rp0,2 (TL) Rm(TL) A%(TL) Rp0,2 (45°) Rm(45°) A%(45°) A-1 415 444 12,2 395 445 12,6 393 439 13,1 A-2 415 440 13,3 398 447 12,7 398 440 13,0 B-1 402 426 13,0 396 446 12,3 385 429 13,2 B-2 405 434 12,8 392 443 11,5 388 435 11,8 C-1 414 442 13,1 391 463 11,9 381 446 13,7 C-2 401 435 13,6 381 450 10,2 374 437 13,7 D-1 410 438 11,0 398 465 9,6 385 444 12,4 D-2 400 434 12,6 381 451 10,0 389 446 12,1 The samples were mechanically tested to determine their static mechanical properties as well as their resistance to crack propagation. The tensile yield strength, breaking strength and elongation at break are given in Table 4. Table 4- Mechanical characteristics expressed in MPa (R<sub>p0.2</sub>, R<sub>m</sub>) or in percentage (A%) Sheet metal R p0.2 (L) R m (L) A%(L) R p0.2 (TL) R m (TL) A%(TL) R p0.2 (45°) R m (45°) A%(45°) A-1 415 444 12.2 395 445 12.6 393 439 13.1 A-2 415 440 13.3 398 447 12.7 398 440 13.0 B-1 402 426 13.0 396 446 12.3 385 429 13.2 B-2 405 434 12.8 392 443 11.5 388 435 11.8 C-1 414 442 13.1 391 463 11.9 381 446 13.7 C-2 401 435 13.6 381 450 10.2 374 437 13.7 D-1 410 438 11.0 398 465 9.6 385 444 12.4 D-2 400 434 12.6 381 451 10.0 389 446 12.1

Le tableau 5 résume les résultats des essais de ténacité pour ces échantillons. Tableau 5 résultats des courbes R pour les éprouvettes de largeur 760 mm. Tôle KR app [MPa√m] KR60 [MPa√m] Δaeff max valid [mm] T-L L-T T-L L-T T-L L-T A-1 135 161 181 213 82 108 A-2 140 168 187 222 134 85 B-1 135 154 178 206 103 109 B-2 135 163 180 216 148 84 C-1 126 155 167 208 140 120 C-2 110 157 142 208 83 100 D-1 124 152 162 201 187 128 D-2 126 158 166 210 131 97 Table 5 summarizes the toughness test results for these samples. Table 5 results of the R curves for the specimens with a width of 760 mm. Sheet metal K R app [MPa√m] KR60 [MPa√m] Δa eff max valid [mm] TL LT TL LT TL LT A-1 135 161 181 213 82 108 A-2 140 168 187 222 134 85 B-1 135 154 178 206 103 109 B-2 135 163 180 216 148 84 C-1 126 155 167 208 140 120 C-2 110 157 142 208 83 100 D-1 124 152 162 201 187 128 D-2 126 158 166 210 131 97

Claims (12)

  1. Method for manufacturing a thin sheet with a thickness of 0.5 to 8 mm from an aluminium-based alloy wherein, successively
    a) a liquid metal bath is produced, comprising
    2.3 to 2.7% by weight Cu,
    1.3 to 1.6% by weight Li,
    0.2 to 0.5% by weight Mg,
    0.1 to 0.5% by weight Mn,
    0.01 to 0.15% by weight Ti,
    a quantity of Zn of less than 0.3% by weight, a quantity of Fe and Si of less than or equal to 0.1% by weight each, and unavoidable impurities with a content of less than or equal to 0.05% by weight each and 0.15% by weight in total,
    b) a plate is cast from said liquid metal bath;
    c) said plate is homogenised at a temperature of between 490°C and 535°C;
    d) said plate is rolled by hot rolling and optionally by cold rolling into a sheet having a thickness of between 0.5 and 8 mm, the entry temperature of the hot rolling being between 400°C and 445°C and the exit temperature of the hot rolling being less than 300°C;
    e) said sheet is solution heat treated at a temperature of between 450°C and 515°C and quenched;
    f) said sheet is stretched in a controlled manner with a permanent deformation of 0.5 to 6%, the cold deformation after solution heat treatment being less than 15%;
    g) aging is carried out, comprising heating at a temperature of between 130° and 170°C and preferably between 150° and 160°C for 5 to 100 hours and preferably 10 to 40 h.
  2. Method according to claim 1, wherein the copper content is between 2.45 and 2.65% by weight and preferably between 2.50 and 2.60% by weight.
  3. Method according to claim 1 or claim 2, wherein the lithium content is between 1.35 and 1.55% by weight and preferably between 1.40% and 1.50% by weight.
  4. Method according to any one of claims 1 to 3, wherein the magnesium content is between 0.25 and 0.45% by weight and preferably between 0.25 and 0.35% by weight.
  5. Method according to any one of claims 1 to 4, wherein the manganese content is between 0.2 and 0.4% by weight and preferably between 0.25 and 0.35% by weight.
  6. Method according to any one of claims 1 to 5, wherein the zinc content is less than 0.1% by weight and preferably less than 0.05% by weight.
  7. Method according to any one of claims 1 to 4, wherein the hot-rolling entry temperature is between 420°C and 440°C and/or the hot-rolling exit temperature is below 290°C.
  8. Thin sheet obtained by the method according to any one of claims 1 to 7, wherein the mean grain size in the thickness measured by the intercepts method on an L/TC section in the L direction in accordance with ASTM E112 and expressed in µm is less than 66 t + 200 where t is the thickness of the sheet expressed in mm, preferably less than 66 t + 150 and preferably less than 66 t + 100.
  9. Thin sheet according to claim 8, wherein the yield strength Rp0.2 of which in the TL direction is at least 370 MPa and the plane strain fracture toughness KR60 of which, measured on test pieces of the CCT760 type (2ao = 253 mm), is at least 170 MPa√m in the T-L direction and in the L-T direction.
  10. Thin sheet according to claim 8 or claim 9 having an yield strength Rp0.2 in the TL direction of at least 393 MPa, a plane strain fracture toughness KR60, measured on test pieces of the CCT760 type (2ao = 253 mm), in the T-L direction, of at least 180 MPa √m, a lithium content of between 1.40 and 1.50% by weight, a copper content of between 2.45 and 2.55% by weight and a magnesium content of between 0.25 and 0.35% by weight.
  11. Thin sheet according to one of claims 8 to 10 wherein the difference in yield strength between the directions L and TL and the yield strength in the direction L is less than 6% and preferably less than 5%.
  12. Use of a thin sheet according to any one of claims 8 to 11 in a fuselage panel for an aircraft.
EP19740635.8A 2018-06-08 2019-05-29 Thin sheets made of aluminium-copper-lithium alloy for aircraft fuselage manufacture Active EP3802897B1 (en)

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