Aluminum—copper—lithium alloy product for a lower wing skin element with improved properties
The invention relates to a method for manufacturing a laminated or forged material, the thickness of which is 14 to 100 mm. The materials according to the invention are particularly suitable for manufacturing airplane underwing elements.
1. A rolled and/or forged product having a thickness of between 14 and 100 mm, wherein at mid-thickness the volume fraction of grains having a brass texture is between 25 and 40% and the texture index is between 12 and 18,
wherein the rolled and/or forged product is produced by a process comprising
(a) casting a slab of alloy comprising, as a percentage by weight,
Cu: 1.8-2.6
Li: 1.3-1.8
Mg: 0.1-0.5
Mn: 0.2-0.4 and Zr<0.04
Ag: 0-0.5
Zn<0.20
Ti: 0.01-0.15
Fe: <0.1
Si: ≤0.1
other elements <0.05 each and <0.15 total, the remainder aluminum with a density less than 2.670 g/cm 3 ,
(b) homogenizing said slab at 480 to 540° C. for 5 to 60 hours,
(c) hot working said slab by rolling and/or forging, the hot working conditions being such that the final hot working temperature is at least 400° C. to obtain a rolled and/or forged product having a thickness of between 14 and 100 mm,
(d) solution-heat treating said product at 490 to 530° C. for 15 minutes to 8 hours,
(e) quenching said product with water,
(f) controlled stretching said product with a permanent deformation of 1 to 6%,
(g) artificially aging said product by heat treatment at 120 to 170° C. for 5 minutes to 100 hours.
2. The rolled and/or forged product according to claim 1 , wherein the copper content of said alloy ranges between 1.9 and 2.3% by weight.
3. The rolled and/or forged product according to claim 1 , wherein the lithium content of said alloy ranges between 1.4 and 1.6% by weight.
4. The rolled and/or forged product according to claim 1 , wherein the magnesium content of said alloy ranges between 0.1 and 0.4% by weight.
5. The rolled and/or forged product according to claim 1 , wherein the silver content of said alloy ranges between 0.05 and 0.25% by weight.
6. The rolled and/or forged product according to claim 1 , wherein the zinc content of said alloy is less than 0.05% by weight, the silicon content of said alloy is less than 0.08% by weight and the iron content of said alloy is less than 0.08% by weight.
7. The rolled and/or forged product according to claim 1 wherein aging is such that the equivalent time t(eq) at 155° C. is between 20 and 40 hours, equivalent time t(eq) at 155° C. being defined by the formula:
t
(
eq
)
=
∫
exp
(
-
11400
/
T
)
dt
exp
(
-
11400
/
T
ref
)
where T (in Kelvin) is the instantaneous treatment temperature, which changes with time t (in hours), and T ref is a reference temperature set at 428 K, and t(eq) is expressed in hours.
8. The rolled and/or forged product according to claim 1 whose thickness is between 20 mm and 50 mm and whose tensile yield strength at mid-thickness TYS (L) is at least 390 MPa, the fracture toughness KappL-T (W=406 mm) is at least 105 MPa√m after aging for 3,000 hours at 85° C. and the number of cycles in condition 6.5 MPa√m<ΔK<16.6 MPa√m is at least 250,000 for a fatigue test performed according to ASTM E647 on CCT type specimens of width W=160 mm taken in direction L-T at ¼ thickness.
9. The rolled and/or forged product according to claim 8 , wherein the tensile yield strength at mid-thickness TYS (L) is at least 395 MPa.
10. The rolled and/or forged product according to claim 8 , wherein the number of cycles in condition 6.5 MPa√m<ΔK<16.6 MPa√m is at least 280,000.
11. The product according to claim 1 as a structural element in aircraft construction, optionally as an aircraft lower wing skin element.
12. The rolled and/or forged product according to claim 1 , wherein the titanium content of said alloy ranges between 0.02 and 0.10% by weight.
13. The rolled and/or forged product according to claim 1 , wherein the density of the slab of alloy is less than 2.640 g/cm 3 .
14. The rolled and/or forged product according to claim 1 , wherein in (b), said homogenizing is at a temperature between 490 to 510° C. for 5 to 60 hours.
15. The rolled and/or forged product according to claim 7 , wherein the equivalent time t(eq) at 155° C. is between 25 and 35 hours.
16. The rolled and/or forged product according to claim 1 , wherein in (a), the slab of alloy consists essentially of, as a percentage by weight,
Cu: 1.8-2.6
Li: 1.3-1.8
Mg: 0.1-0.5
Mn: 0.2-0.4 and Zr<0.04
Ag: 0-0.5
Zn<0.20
Ti: 0.01-0.15
Fe: <0.1
Si: ≤0.1
other elements <0.05 each and <0.15 total, the remainder aluminum with a density less than 2.670 g/cm 3 .
17. The rolled and/or forged product according to claim 1 , wherein the rolled and/or forged product is produced by a process comprising:
(c) hot working said slab by rolling and/or forging, the hot working conditions being such that the final hot working temperature is at least 410° C. to obtain a rolled and/or forged product having a thickness of between 14 and 100 mm.