Thin sheets made of an aluminium-copper-lithium alloy for producing airplane fuselages

1. A method for producing a sheet of thickness 0.5 to 3.3 mm of essentially unrecrystallized structure made of an aluminum-based alloy said method comprising, successively

a) a molten metal bath is prepared comprising

2.6 to 3.4% by weight of Cu,

0.5 to 1.1% by weight of Li,

0.1 to 0.4% by weight of Ag,

0.2 to 0.8% by weight of Mg,

0.11 to 0.20% by weight of Zr,

0.01 to 0.15% by weight of Ti,

optionally at least one element chosen among Mn, V, Cr, Sc, and Hf, the quantity of element, if chosen, being from 0.01 to 0.8% by weight for Mn, 0.05 to 0.2% by weight for V, 0.05 to 0.3% by weight for Cr, 0.02 to 0.3% by weight for Sc, 0.05 to 0.5% by weight for Hf,

a quantity of Zn less than 0.6% by weight, a quantity of Fe and Si less than or equal to 0.1% by weight each, and inevitable impurities with a content less than or equal to 0.05% by weight each and 0.15% by weight in total,

b) casting a slab from said molten metal bath

c) homogenizing said slab at a temperature between 450° C. and 515° C.;

d) hot rolling said slab into a plate of thickness between 4 and 12 mm;

e) cold rolling said plate into a sheet of final thickness between 0.5 and 3.3 mm, the reduction in thickness by cold rolling being between 1 and 3.5 mm;

f) performing heat treatment during which the sheet reaches a temperature between 300° C. and 450° C. for at least thirty minutes;

g) solution heat treating said sheet at a temperature between 450° C. and 515° C. and quenching;

h) controlled stretching said sheet with a permanent deformation of 0.5 to 5%, cold working after solution heat treatment being less than 15%;

i) performing aging at a temperature between 130° C. and 170° C. and optionally between 150° C. and 160° C. for 5 to 100 hours and preferably for 10 to 40 hours.

2. The method according to claim 1 , wherein the copper content lies between 2.8 and 3.1% by weight and optionally between 2.8 and 3.0% by weight.

3. The method according to claim 1 , wherein the lithium content lies between 0.55 and 0.75% by weight and optionally between 0.60 and 0.73% by weight.

4. A sheet of essentially unrecrystallized granular structure, wherein the sheet is obtained by a process comprising the following performed in succession,

a) preparing a molten metal bath comprising

2.6 to 3.4% by weight of Cu,

0.5 to 1.1% by weight of Li,

0.1 to 0.4% by weight of Ag,

0.2 to 0.8% by weight of Mg,

0.11 to 0.20% by weight of Zr,

0.1 to 0.15% by weight of Ti,

optionally at least one element chosen among Mn, V, Cr, Sc, and Hf, the quantity of element, if chosen, being from 0.01 to 0.8% by weight for Mn, 0.05 to 0.2% by weight for V, 0.05 to 0.3% by weight for Cr, 0.02 to 0.3% by weight for Sc, 0.05 to 0.5% by weight for Hf,

a quantity of Zn less than 0.6% by weight, a quantity of Fe and Si less than equal to 0.1by weight each, and inevitable impurities with a content less than or equal to 0.05% by weight each and 0.15% by weight in total,

e) casting a slab from said molten metal bath

f) homogenizing said slab at a temperature between 450° C. and 515° C.;

g) hot rolling said slab into a plate of thickness between 4 and 12 mm;

e) cold rolling said plate into a sheet of final thickness between 0.5 and 3.3 mm, the reduction in thickness by cold rolling being between 1 and 3.5 mm;

f) performing heat treatment during which the sheet reaches a temperature between 300° C. and 450° C. for at least thirty minutes;

g) solution heat treating said sheet at a temperature between 450° C. and 515° C. and quenching;

h) controlled stretching said sheet with a permanent deformation of 0.5 to 5%, cold working after solution heat treatment being less than 15%;

i) performing aging at a temperature between 130° C. and 170° C. and optionally between 150° C. and 160° C. for 5 to 100 hours and preferable for 10 to 40 hours,

wherein the yield stress R p0.2 in the T-L direction is at least 395 MPa, and the fracture toughness in plane strain K app , measured on test pieces of type CCT760 (2ao=253 mm) in the T-L direction is at least 150 MPa√m.

5. The sheet according to claim 4 wherein the lithium content lies between 0.55 and 0.75% by weight, the elongation of which is at least 14% in the T-L direction.

6. The sheet according to claim 5 , wherein the magnesium content lies between 0.40 and 0.65% by weight, whose yield stress R p0.2 in the T-L direction is at least 405 MPa, whose fracture toughness in plane strain K app , measured on test pieces of type CCT760 (2ao=253 mm) in the T-L direction is at least 160 MPa√m.

7. The sheet according to claim 5 wherein the copper content lies between 2.8 and 3.0% by weight, and the elongation of which is at least 15% in the T-L direction.

8. The sheet according to claim 5 , wherein the magnesium content lies between 0.40 and 0.65% by weight, the copper content of which lies between 2.8 and 3.0%, the yield stress R p0.2 in the T-L direction is at least 410 MPa, whose fracture toughness in plane strain K app , measured on test pieces to type CCT760 (2ao=253 mm), in the T-L direction of at least 163 MPa√m and whose elongation in the T-L direction is at least 16%.

9. A sheet according to claim 4 shaped into an aircraft fuselage panel.

10. The sheet according to claim 4 , wherein recrystallization rate at half thickness is less than 10%.

11. The sheet according to claim 4 , wherein the lithium content is between 0.60 and 0.73% by weight.

12. The sheet according to claim 4 , wherein the Ag content is between 0.2 and 0.3% by weight.

13. The sheet according to claim 4 , wherein the final thickness is between 1.2 and 2.8 mm.

14. The sheet according to claim 4 , wherein the reduction in thickness by cold rolling is between 1 and 3.0 mm.

15. The sheet according to claim 4 , wherein cold working after solution heat treatment is less than 10%.

16. The sheet according according to claim 4 , wherein the molten metal bath consists essentially of

a. 2.6 to 3.4% by weight of Cu,

b. 0.5 to 1.1% by weight of Li,

c. 0.1 to 0.4% by weight of Ag,

d. 0.2 to 0.8% by weight of Mg,

e. 0.11 to 0.20% by weight of Zr,

f. 0.01 to 0.15% by weight of Ti,

optionally at least one element chosen among Mn, V, Cr, Sc, and Hf, the quantity of element, if chosen, being from 0.01 to 0.8% by weight for Mn, 0.05 to 0.2% by weight for V, 0.05 to 0.3% by weight for Cr, 0.02 to 0.3% by weight for Sc, 0.05 to 0.5% by weight for Hf,

a quantity of Zn less than 0.6% by weight, a quantity of Fe and Si less than or equal to 0.1% by weight each, and inevitable impurities with a content less than or equal to 0.05% by weight each and 0.15% by weight in total.

17. The sheet according according to claim 4 , wherein the molten metal bath consists of

a. 2.6 to 3.4% by weight of Cu,

b. 0.5 to 1.1% by weight of Li,

c. 0.1 to 0.4% by weight of Ag,

d. 0.2 to 0.8% by weight of Mg,

e. 0.11 to 0.20% by weight of Zr,

f. 0.01 to 0.15% by weight of Ti,

optionally at least one element chosen among Mn, V, Cr, Sc, and Hf, the quantity of element, if chosen, being from 0.01 to 0.8% by weight for Mn, 0.05 to 0.2% by weight for V, 0.05 to 0.3% by weight for Cr, 0.02 to 0.3% by weight for Sc, 0.05 to 0.5% by weight for Hf,

a quantity of Zn less than 0.6% by weight, a quantity of Fe and Si less than or equal to 0.1% by weight each, and inevitable impurities with a content less than or equal to 0.05% by weight each and 0.15% by weight in total.

18. The sheet according to claim 5 , wherein the yield stress R p0.2 in the T-L direction is at least 410 MPa, and the fracture toughness in plane strain K app , measured on test pieces to type CCT760 (2ao =253 mm), in the T-L direction is at least 165 MPa√m.

19. The sheet according to claim 17 , wherein the lithium content is from 0.55 and 0.75% by weight, the magnesium content is from 0.40 and 0.65% by weight, the copper content is from 2.8 and 3.0% by weight, the Ag content is from 0.2 and 0.3% by weight; and

wherein the yield stress R p0.2 in the T-L direction is at least 410 MPa, whose fracture toughness in plane strain K app , measured on test pieces to type CCT760 (2ao =253 mm), in the T-L direction of at least 163 MPa√m and whose elongation in the T-L direction is at least 16%.

20. The sheet according to claim 19 , wherein the final thickness of the sheet is from 1.2 and 2.8 mm.