Aluminum-copper-lithium alloy thin sheets with improved toughness, and process for manufacturing an aluminum-copper-lithium alloy thin sheet

A method for manufacturing a sheet with a thickness of between 4 and 12.7 mm made from aluminum-based alloy wherein, successively,

• a) producing a liquid metal bath consisting of
• 2.2 to 2.7% by weight Cu,
• 1.3 to 1.6% by weight Li,
• no more than 0.1% by weight Ag,
• 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 or equal to 0.3% by weight, a quantity of Fe and of Si of less than or equal to 0.1% by weight each, the remainder being aluminum and unavoidable impurities with a content of less than or equal to 0.05% by weight each, and 0.15% by weight in total, the remainder aluminum,
• b) casting a slab from said liquid-metal bath;
• c) homogenizing said slab at a temperature of between 490° C. and 535 ° C.;
• d) rolling said homogenized slab by hot rolling into a sheet having a thickness of between 4 and 12.7 mm, a hot-rolling input temperature being between 420° C. and 445° C. and a hot-rolling output temperature being less than 300° C.;
• e) solution heat treating said sheet at a temperature of between 450° C. and 535° C. for at least 5 min, with a mean rate of heating of said sheet of at least 17° C./min between 300° C. and 400° C., and said solution heat treated sheet is quenched in water;
• f) stretching said quenched sheet in a controlled manner with a permanent deformation of 0.5 to 6%, a cold deformation after solution heat treatment being less than 15%;
• g) aging said sheet, said aging comprising heating at a temperature of between 130 and 170° C. so that yield strength in a long-transverse direction Rp0.2 (LT) is between 350 and 380 MPa, and wherein the sheet is recrystallized.