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

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 Rp0.2 in the T-L direction is at least 395 MPa, and the fracture toughness in plane strain Kapp, measured on test pieces of type CCT760 (2ao=253 mm) in the T-L direction is at least 150 MPa√m.