EP3201372B1 - Isotropic sheets of aluminium-copper-lithium alloys for the fabrication of fuselages of aircrafts and method of manuacturing same - Google Patents

Description

Field of the invention

The invention relates to aluminum-copper-lithium alloy rolled products, more particularly such products, their manufacturing and use processes, intended in particular for aeronautical and aerospace construction.

State of the art

Rolled aluminum alloy products are developed to produce fuselage elements intended in particular for the aeronautical industry and the aerospace industry.

Aluminum - copper - lithium alloys are particularly promising for manufacturing this type of product.

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, increases the mechanical strength.

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 by means of suitable hardening and tempering. This patent recommends in particular the composition, in percentage by weight, Cu = 3.0 - 4.5, Li = 0.7 - 1.1, Ag = 0 - 0.6, Mg = 0.3-0.6 and Zn = 0 - 0.75.

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 a compromise between toughness and mechanical resistance.

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.

The patent application US 2009/142222 A1 describes alloys comprising (in weight%), 3.4 to 4.2% Cu, 0.9 to 1.4% Li, 0.3 to 0.7% Ag, 0.1 to 0, 6% Mg, 0.2-0.8% Zn, 0.1-0.6% Mn and 0.01-0.6% of at least one element for control of granular structure. This application also describes a process for manufacturing spun products.
The patent application US 2011/0247730 describes alloys comprising (in wt%), 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 of between 6.1 and 17, this alloy being not very sensitive to wringing.
The patent application CN101967588 describes alloys of composition (wt%) 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, she teaches the combined addition of zirconium and manganese.
The patent application US 2011/209801 relates to wrought products such as extruded, rolled and / or forged products, made of an aluminum-based alloy comprising, in% by weight, Cu: 3.0-3.9; Li: 0.8-1.3; Mg: 0.6 - 1.0; Zr: 0.05-0.18; Ag: 0.0 - 0.5; Mn: 0.0 - 0.5; Fe + Si <= 0.20; at least one of Ti: 0.01-0.15; Sc: 0.05 - 0.3; Cr: 0.05 - 0.3; Hf: 0.05 - 0.5; other elements <= 0.05 each and <= 0.15 in total, remainder of aluminum, the products being particularly useful for producing thick aluminum products intended to produce structural elements for the aeronautical industry.

The characteristics required for aluminum sheets intended for fuselage applications are described for example in the patent EP 1,891,247 . It is particularly desirable that the sheet has a high elastic limit (to resist buckling) as well as a tenacity under high plane stress, characterized in particular by a high value of intensity factor of apparent stress at break (K _app ) high and a long curve R.

The patent EP 1 966 402 describes an alloy comprising 2.1 to 2.8 wt% Cu, 1.1 to 1.7 wt% Li, 01 to 0.8 wt% Ag, 0.2 to 0.6 wt% 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 inevitable impurities at a content of less than or equal to 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.

WO2006131627 discloses a low density aluminum-based alloy useful in an aircraft structure for fuselage sheet applications exhibiting high mechanical strength, high toughness and high corrosion resistance, containing in% by weight, 2, 7 to 3.4 Cu, 0.8 to 1.4 Li, 0.1 to 0.8 Ag, 0.2 to 0.6 Mg and an element such as Zr, Mn, Cr, Sc , Hf, Ti or a combination thereof, the amount of which, in% by weight, is 0.05 to 0.13 for Zr, 0.05 to 0.8 for Mn, 0.05 to 0.3 for Cr and Sc, 0.05 to 0.5 for Hf and 0.05 to 0.15 for Ti. The amount of Cu and Li is determined according to the formula Cu (% by weight) + 5/3 Li (% by weight) <5.2.

Tsivoulas D. et al. “Effects of combined Zr and Mn additions on dispersoid formation and recrystallization behavior of 2198” in the journal “Advanced Materials Research” (Vol. 89-91, 2010, pp568-573 ) have shown that the addition of Mn to an AA2198 aluminum alloy sheet containing Zr increases the propensity for recrystallization.
Tsivoulas D. et al. "The effect of Mn and Zr dispersoid forming additions on recrystallization resistance in Al-Cu-Li AA2198 sheet" in the journal "Acta Materialia" (77 (2014), pp1-16 ) mentioned that the anti-recrystallizing power of Zr decreases with the addition of Mn and that this effect increases if the content of Zr decreases and the content of Mn increases.
The fuselage sheets can be stressed in several directions, and isotropic thin sheets having high and balanced properties in mechanical strength in the L and TL directions and in toughness for the LT and TL directions are in great demand. In addition, it has been observed that thin sheets obtained with certain alloys exhibiting high properties at certain thicknesses, for example 4 mm, may in certain cases have lower or anisotropic properties at another thickness, for example 2.5 mm. It is not it is often not industrially advantageous to use different alloys for different thicknesses and an alloy making it possible to achieve high and isotropic properties whatever the thickness would be particularly advantageous.

There is a need for thin sheets, in particular 0.5 to 9 mm thick, made of an aluminum-copper-lithium alloy having improved and isotropic properties compared to those of known products, in particular in terms of mechanical resistance in L and TL directions and in tenacity for the LT and TL directions, and this over the whole of this thickness range.

Object of the invention

The object of the invention is a sheet of thickness 0.5 to 9 mm with an essentially recrystallized granular structure according to claim 1.

Another object of the invention is the method of manufacturing a sheet according to the invention of thickness 0.5 to 9 mm in aluminum-based alloy according to claim 10.

Yet another object of the invention is the use of a sheet according to the invention in a fuselage panel for an aircraft.

Description of figures

• Figure 1 - R curves obtained in the LT direction on sheets 4 to 5 mm thick for specimens of 760 mm width.
• Figure 2 - R curves obtained in the LT direction on 1.5 to 2.5 mm thick sheets for 760 mm wide specimens.

Description of the invention

Unless otherwise indicated, all indications concerning the chemical composition of 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. Unless stated otherwise, the definitions of metallurgical states given in European standard EN 515 apply.
The static mechanical properties in tension, 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 NF EN ISO 6892-1, the sampling and direction of the test being defined by standard EN 485-1. In the context of the present invention, an essentially non-recrystallized granular structure is called a granular structure such that the rate of recrystallization at ½ thickness is less than 30% and preferably less than 10% and an essentially recrystallized granular structure is called a structure. granular 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 surface fraction on a metallographic section occupied by recrystallized grains.
Grain sizes are measured according to ASTM E112.

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 K _C , in d ' other terms the intensity factor which makes the crack unstable, is calculated from the curve R. The stress intensity factor K _CO is also calculated by attributing the initial crack length to the onset of the monotonic load, to the critical load. These two values are calculated for a specimen of the required shape. K _app represents the factor Kco corresponding to the test piece which was used to carry out the curve test R. K _eff represents the factor K _C corresponding to the test piece which was used to carry out the curve test R. Kr60 represents the factor of effective stress intensity for an effective crack extension Δaeff of 60 mm. Unless stated otherwise, the crack size at the end of the fatigue pre-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.

Unless stated otherwise, the definitions of standard EN 12258 apply.

The copper content of the products according to the invention is between 2.8 and 3.2% by weight. In an advantageous embodiment of the invention, the copper content is between 2.9 and 3.1% by weight.

The lithium content of the products according to the invention is between 0.5 and 0.8% by weight and preferably between 0.55% and 0.75% by weight. Advantageously, the lithium content is at least 0.6% by weight. In one embodiment of the invention, the lithium content is between 0.64% and 0.73% by weight. 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 high value of toughness and / or a sufficient elastic limit.

The magnesium content of the products according to the invention is between 0.2 and 0.7% by weight, preferably between 0.3 and 0.5% by weight and preferably between 0.35 and 0.45%. in weight.

The manganese content is between 0.2 and 0.35% by weight and preferably between 0.25 and 0.35% by weight. The addition of manganese in the claimed amount makes it possible to control the granular structure while avoiding the detrimental effect on the toughness that would generate too high a content.

The silver content is between 0.1 and 0.3% by weight. In an advantageous embodiment of the invention, the silver content is between 0.15 and 0.28% by weight.

The titanium content is between 0.01 and 0.15% by weight. Advantageously, the titanium content is at least 0.02% by weight and preferably at least 0.03% by weight. In an advantageous embodiment of the invention, the titanium content is at most 0.1 % by weight and preferably not more than 0.05% by weight. The addition of titanium helps to control the granular structure, especially during casting.

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 improving the trade-off between mechanical resistance and tolerance to damage.

The zinc content is 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.
Unavoidable impurities are kept at a content of less than or equal to 0.05% by weight each and 0.15% by weight in total.
In particular, the zirconium content is less than or equal to 0.05% by weight, preferably less than or equal to 0.04% by weight and preferably less than or equal to 0.03% by weight.
The process for manufacturing sheets according to the invention comprises stages of production, casting, rolling, dissolving, quenching, controlled traction and tempering.
In a first step, a liquid metal bath is produced so as to obtain an aluminum alloy of composition according to the invention.
The liquid metal bath is then cast in a rolling plate form.
The rolling plate is then homogenized at a temperature between 480 ° C and 535 ° and preferably between 490 ° C and 530 ° C and preferably between 500 ° C and 520 ° C. The homogenization time is preferably between 5 and 60 hours.
In the context of the invention, a homogenization temperature that is too low or the absence of homogenization does not make it possible to achieve improved and isotropic properties compared to those of known products, in particular in terms of mechanical resistance in L and TL directions and toughness for the LT and TL directions, over the whole of this thickness range.
After homogenization, the rolling plate is generally cooled to room temperature before being preheated with a view to being hot-deformed. Preheating has for objective of reaching a temperature preferably between 400 and 500 ° C allowing deformation by hot rolling.
Hot rolling and optionally cold rolling is carried out so as to obtain a sheet thickness 0.5 to 9 mm.
Advantageously, during hot rolling, a temperature above 400 ° C. is maintained up to the thickness of 20 mm and preferably a temperature above 450 ° C. up to the thickness of 20 mm. Intermediate heat treatments during rolling and / or after rolling can be carried out in some cases. Preferably, however, the process does not include an intermediate heat treatment during rolling and / or after rolling. The sheet thus obtained is then placed in solution by heat treatment between 450 and 535 ° C, preferably between 490 ° C and 530 ° C and preferably between 500 ° C and 520 ° C, preferably for 5 min to 2 hours , then soaked. Advantageously, the duration of the solution is at most 1 hour so as to minimize the surface oxidation.
It is known to those skilled in the art that the precise conditions for dissolving must be chosen as a function of the thickness and of the composition so as to place the hardening elements in solid solution.
The sheet then undergoes cold deformation by controlled traction with a permanent deformation of 0.5 to 5% and preferably of 1 to 3%. Known steps such as rolling, leveling, smoothing, straightening and shaping can optionally be carried out after dissolving and quenching and before or after controlled traction, however total cold deformation after dissolving and quenching should remain below 15% and preferably below 10%. High cold deformations after dissolving and quenching in fact cause the appearance of numerous shear bands crossing several grains, these shear bands not being desirable.
Typically, the hardened sheet may be subjected to a smoothing or leveling step, before or after the controlled traction. The term “smoothing / leveling” is understood here to mean a cold deformation step without permanent deformation or with a permanent deformation less than or equal to 1%, making it possible to improve the flatness.

Tempering is carried out comprising heating at a temperature between 130 and 170 ° C and preferably between 150 and 160 ° C for 5 to 100 hours and preferably 10 to 40 hours. Preferably, the final metallurgical state is a T8 state.

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 returned.

The granular structure of the sheets according to the invention is essentially recrystallized. The combination of the composition according to the invention and the transformation parameters makes it possible to control the anisotropy index of the recrystallized grains. Thus the sheets according to the invention are such that the anisotropy index of the grains measured at mid-thickness according to standard ASTM E112 by the method of intercepts in the L / TC plane is less than 20, preferably less than 15 and preferably less than 10. Advantageously for sheets whose thickness is less than or equal to 3 mm, the anisotropy index of the grains measured at mid-thickness according to standard ASTM E112 by the method of intercepts in the L plane / TC is less than or equal to 8, preferably less than or equal to 6 and preferably less than or equal to 4.

• une ténacité en contrainte plane Kapp, mesurée sur des éprouvettes de type CCT760 (2ao = 253 mm), dans la direction L-T et dans la direction T-L d'au moins 140 MPa√m et préférentiellement d'au moins 150 MPa√m et une limite R_P0,2 dans les directions L et TL d'au moins 360 MPa et de préférence d'au moins 365 MPa,
• une ténacité en contrainte plane Kr60, mesurée sur des éprouvettes de type CCT760 (2ao = 253 mm), dans la direction L-T et dans la direction T-L supérieur à 190 MPa√m et préférentiellement supérieur à 200 MPa√m et une résistance à rupture Rm dans les directions L et TL d'au moins 410 MPa et de préférence d'au moins 415 MPa,
  et au moins une des propriétés suivantes :
  • un rapport entre la ténacité en contrainte plane Kapp, mesurée sur des éprouvettes de type CCT760 (2ao = 253 mm), dans les direction T-L et L-T, Kapp(T-L) / Kapp (L-T), compris entre 0,85 et 1,15 et de préférence entre 0,90 et 1,10
  • un rapport entre la résistance à rupture Rm dans les directions L et TL, Rm(L) / Rm(TL), inférieur à 1,06 et de préférence inférieur à 1,05.

The sheets according to the invention have advantageous properties whatever the thickness of the products.
The sheets according to the invention, the thickness of which is between 0.5 and 9 mm and particularly between 1.5 and 6 mm, advantageously exhibit in the T8 state at least one of the following pairs of properties

• a plane stress tenacity Kapp, measured on specimens of the CCT760 type (2ao = 253 mm), in the LT direction and in the TL direction of at least 140 MPa√m and preferably at least 150 MPa√m and a limit R _P0.2 in the L and TL directions of at least 360 MPa and preferably at least 365 MPa,
• a plane stress tenacity Kr60, measured on specimens of the CCT760 type (2ao = 253 mm), in the LT direction and in the TL direction greater than 190 MPa√m and preferably greater than 200 MPa√m and a tensile strength Rm in the L and TL directions of at least 410 MPa and preferably at least 415 MPa,
  and at least one of the following properties:
  • a ratio between the tenacity in plane stress Kapp, measured on specimens of type CCT760 (2ao = 253 mm), in the direction TL and LT, Kapp (TL) / Kapp (LT), between 0.85 and 1.15 and preferably between 0.90 and 1.10
  • a ratio between the breaking strength Rm in the L and TL directions, Rm (L) / Rm (TL), less than 1.06 and preferably less than 1.05.

Without being bound by a particular theory, the present inventors believe that the combination between the composition, in particular the limited content of zirconium, the addition of manganese and the selected amount of magnesium and the transformation process, in particular the homogenization temperature and hot rolling, allows to obtain the claimed advantageous properties.

The resistance to corrosion, in particular to intergranular corrosion, to leaf corrosion and to stress 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.

The use of sheets according to the invention in a fuselage panel for an aircraft is advantageous. The sheets according to the invention are also advantageous in aerospace applications such as the manufacture of rockets.

Example

In this example, Al-Cu-Li alloy sheets were prepared. 7 plates whose composition is given in Table 1 were cast. Table 1. Composition in% by weight of the plates Alloy Cu Li Mg Zr Mn Ag Fe Yes Ti AT 3.2 0.73 0.68 0.14 <0.01 0.26 0.03 0.04 0.03 B 3.0 0.70 0.64 0.17 <0.01 0.27 0.02 0.03 0.03 VS 3.0 0.73 0.35 0.15 <0.01 0.27 0.02 0.03 0.03 D 2.7 0.75 0.58 0.14 <0.01 0.28 0.03 0.02 0.03 E 2.9 0.73 0.45 0.14 <0.01 0.29 0.04 0.02 0.03 F 2.9 0.68 0.42 0.03 0.28 0.28 0.03 0.02 0.03 G 2.9 0.75 0.44 0.05 0.28 0.26 0.03 0.02 0.03

The plates were homogenized for 12 hours at 505 ° C. The plates were hot rolled to obtain sheets with a thickness between 4.2 to 6.3 mm. Some sheets were then cold rolled to a thickness between 1.5 and 2.5 mm. Details of the sheets obtained and the tempering conditions are given in Table 2. Table 2: detail of the sheets obtained and the tempering conditions Sheet metal Thickness after hot rolling (mm) Thickness after cold rolling (mm) Tempering time at 155 ° C (h) A # 1 4.2 - 36 A # 2 4.4 1.5 36 B # 1 4.6 - 36 B # 2 4.4 1.5 36 C # 1 4.3 - 24 C # 2 4.4 1.5 24 D # 1 4.3 - 40 D # 2 6.3 2.5 40 E # 1 4.3 - 36 E # 2 6.3 2.5 36 F # 1 4.2 - 28 F # 2 4.2 2.5 28 G # 1 4.2 - 28 G # 2 4.2 2.5 28

After hot and optionally cold rolling, the sheets were put into solution at 505 ° C. then smoothed, pulled with a permanent elongation of 2% and tempered. The tempering conditions are not all the same because the increase in the yield strength with the tempering time differs from one alloy to another. An attempt has been made to obtain a “peak” elasticity limit while limiting the period of tempering. The income conditions are given in Table 2.

The granular structure of the samples was characterized from the microscopic observation of the cross sections after anodic oxidation under polarized light. The grain structure of the plates was essentially non-recrystallized for all plates except for the D # 2 E # 2 F # 1, F # 2, G # 1 and G # 2 plates where the grain structure was essentially recrystallized.
For sheets whose granular structure was essentially recrystallized, the grain size was determined in the L / TC plane at mid-thickness according to the standard ASTM E112 by the method of intercepts from the microscopic observation of the cross sections after oxidation. anodic under polarized light. The anisotropy index is the ratio of the grain size measured in the L direction divided by the grain size measured in the TC direction. The results are shown in Table 3. Table 3: Grain sizes measured for samples whose granular structure was essentially recrystallized Sheet metal Direction L (µm) Direction TC (µm) Anisotropy index D # 2 1260 21 60 E # 2 1100 23 48 F # 1 540 59 9 F # 2 135 37 4 G # 1 678 56 12 G # 2 317 46 7

The samples were mechanically tested to determine their static mechanical properties as well as their toughness. The mechanical characteristics were measured at full thickness.

The tensile yield strength, ultimate strength and elongation at break are provided in Table 4. Table 4: Mechanical characteristics expressed in MPa (R _p0,2, R _m) 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 _m (L) / R _m (TL) A # 1 469 513 12.2 439 481 15.8 1.07 A # 2 475 522 11.7 441 489 14.0 1.07 B # 1 431 483 13.5 419 462 16.1 1.05 B # 2 431 486 12.9 414 460 17.1 1.06 C # 1 430 471 13.6 411 455 15.5 1.04 C # 2 423 472 12.2 399 451 15.9 1.05 D # 1 420 462 13.0 384 428 16.3 1.08 D # 2 403 437 11.6 371 428 13.9 1.02 E # 1 453 487 12.5 428 464 15.9 1.05 E # 2 433 464 11.4 395 458 11.4 1.01 F # 1 392 430 12.5 369 420 12.4 1.02 F # 2 400 437 11.9 368 419 13.4 1.04 G # 1 402 432 13.4 372 424 12.7 1.02 G # 2 412 440 12.9 378 426 13.1 1.03

Table 5 summarizes the results of the toughness tests on 760 mm wide CCT specimens for these samples. Table 5 results of the R curves for the CCT specimens with a width of 760 mm. Sheet metal Kapp Kr60 Kapp (TL) / Kapp (LT) [MPa√m] [MPa√m] TL LT TL LT A # 1 187 161 247 213 1.16 A # 2 160 114 210 151 1.40 B # 1 180 178 238 238 1.01 B # 2 167 124 223 166 1.35 C # 1 182 165 242 219 1.10 C # 2 154 127 203 162 1.21 D # 1 174 150 230 200 1.16 D # 2 147 151 196 201 0.97 E # 1 181 159 240 213 1.14 E # 2 137 164 181 219 0.84 F # 1 154 169 203 223 0.91 F # 2 158 168 208 224 0.94 G # 1 153 172 202 228 0.89 G # 2 158 172 208 229 0.92

The Figures 1 and 2 illustrate the remarkable tenacity of Examples F and G according to the invention, in particular in the LT direction.
Examples F and G demonstrate that it is possible to obtain thin sheets according to the invention which exhibit improved and isotropic properties compared to those obtained from the other Examples A to E, and in particular compared to Example C , and this over a wide range of typical thickness of said thin sheets.

Claims (13)

1. Plate having a thickness from 0.5 to 9 mm and a granular structure such that the degree of recrystallisation at half thickness is greater than 70% where the degree of recrystallisation is the proportion of surface on a metallographic section occupied by recrystallised grains, made from an aluminium-based alloy comprising

   2.8 to 3.2% by weight Cu,

   0.5 to 0.8% by weight Li,

   0.1 to 0.3% by weight Ag,

   0.2 to 0.7% by weight Mg,

   0.2 to 0.35% by weight Mn,

   0.01 to 0.15% by weight Ti,

   a quantity of Zn of less than 0.2% by weight, a quantity of Fe and Si of less than or equal to 0.1% by weight each, and unavoidable impurities, including zirconium, to a proportion of less than or equal to 0.05% by weight each and 0.15% by weight in total, the remainder aluminium,
   said plate being obtained by a method comprising casting, homogenisation, hot rolling and optionally cold rolling, solution heat treatment, quenching and aging.
2. Plate according to claim 1, the copper content of which is between 2.9 and 3.1% by weight.
3. Plate according to claim 1 or claim 2, the lithium content of which is between 0.55 and 0.75% by weight and preferably between 0.64 and 0.73% by weight.
4. Plate according to any of claims 1 to 3, the silver content of which is between 0.15 and 0.28% by weight.
5. Plate according to any of claims 1 to 4, the magnesium content of which is between 0.3 and 0.5% by weight and preferably between 0.35 and 0.45% by weight.
6. Plate according to any of claims 1 to 5, the zirconium content of which is less than or equal to 0.03% by weight.
7. Plate according to any of claims 1 to 6, the manganese content of which is between 0.25 and 0.35% by weight.
8. Plate according to any of claims 1 to 7, characterised in that the anisotropy index of the grains measured at half thickness in accordance with ASTM E112 by the intercept method in the L/TC plane is less than 20, and preferably less than 15 and preferably less than 10.
9. Plate according to any of claims 1 to 8, the thickness of which is between 0.5 and 9 mm and particularly between 1.5 and 6 mm have in the T8 temper at least one of the following pairs of properties:

   - a toughness under plane strain stress Kapp, measured in accordance with ASTM E 561 on test pieces of the CCT760 2ao = 253 mm type, in the L-T direction and in the T-L direction, of at least 140 MPa√m and preferentially at least 150 MPa√m and a tensile yield strength R_P0.2 measured in accordance with NF EN ISO 6892-1 in the L and TL directions in accordance with EN 485-1 of at least 360 MPa and preferably at least 365 MPa,

   - a toughness under plane strain stress Kr60, measured in accordance with ASTM E 561 on test pieces of the CCT760 2ao = 253 mm type, in the L-T direction and in the T-L direction, greater than 190 MPa√m and preferentially greater than 200 MPa√m and an ultimate tensile strength Rm measured in accordance with NF EN ISO 6892-1 in the L and TL directions in accordance with EN 485-1 of at least 410 MPa and preferably at least 415 MPa,

   and at least one of the following properties:

   - a ratio between the toughness under plane strain stress Kapp, measured in accordance with ASTM E 561 on test pieces of the CCT760 2ao = 253 mm type, in the T-L and L-T directions, Kapp (T-L) /Kapp (L-T), of between 0.85 and 1.15 and preferably between 0.90 and 1.10

   - a ratio between the ultimate tensile strength Rm measured in accordance with NF EN ISO 6892-1 in the L and TL directions in accordance with EN485-1, Rm(L)/Rm(TL), of less than 1.06 and preferably less than 1.05.
10. Method for manufacturing a plate with a thickness of 0.5 to 9 mm according to any of claims 1 to 8, in which, successively

    a) a liquid metal bath is produced so as to obtain an aluminium alloy comprising

    2.8 to 3.2% by weight Cu,

    0.5 to 0.8% by weight Li,

    0.1 to 0.3% by weight Ag,

    0.2 to 0.7% by weight Mg,

    0.2 to 0.35% by weight Mn,

    0.01 to 0.15% by weight Ti,

    a quantity of Zn of less than 0.2% by weight, a quantity of Fe and Si of less than or equal to 0.1% by weight each, and unavoidable impurities, including zirconium, to a proportion of less than or equal to 0.05% by weight each and 0.15% by weight in total, the remainder aluminium;

    b) an ingot is cast from said bath of liquid metal;

    c) said ingot is homogenised at a temperature of between 480°C and 535°C;

    d) said ingot is rolled by hot rolling and optionally cold rolling into a plate having a thickness of between 0.5 mm and 9 mm;

    e) solution heat treatment is carried out at a temperature of between 450°C and 535°C and said plate is quenched;

    h) said plate is stretched in a controlled manner with a permanent deformation set of 0.5 to 5%, the total cold deformation set after solution heat treatment and quenching being less than 15%;

    i) aging is carried out, comprising heating to 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 hours.
11. Method according to claim 10, in which the homogenisation temperature is between 490° and 530°C and preferably between 500° and 520°C.
12. Method according to claim 10 or claim 11, in which, during the hot rolling, a temperature above 400° is maintained up to the thickness of 20 mm and preferably a temperature of 450° up to the thickness of 20 mm.
13. Use of a plate according to any of claims 1 to 9 in an aircraft fuselage panel.

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