Aluminium-copper-lithium alloy sheets for producing aeroplane fuselages

Abstract

The invention concerns a sheet 0.5 to 8 mm thick made from aluminium alloy. The sheet can be obtained by a method comprising casting, homogenising, hot rolling and optionally cold rolling, solution heat treatment, quenching and tempering, the composition and the tempering being combined in such a way that the elasticity limit in the longitudinal direction R p0.2 (L) is between 395 and 435 MPa. A sheet according to the invention is particularly advantageous for producing aircraft fuselage panels.

1 . A sheet measuring 0.5 to 8 mm thick made of an aluminum-based alloy composition comprising
 2.6 to 3.0% by weight of Cu,   0.5 to 0.8% by weight of Li,   0.1 to 0.4% by weight of Ag,   0.2 to 0.7% by weight of Mg,   0.06 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 0.2% by weight, a quantity of Fe and Si less than or equal to 0.1% by weight each, and inevitable impurities having a content less than or equal to 0.05% by weight each and 0.15% by weight in total,   said sheet being obtained by a method comprising casting, homogenization, hot rolling and optionally cold rolling, solution heat treatment, quenching and aging, the composition and the aging being combined in such a way that the yield stress in the longitudinal direction R p0.2 (L) is between 395 and 435 Mpa.   
     
     
         2 . The sheet according to  claim 1 , the copper content of which lies between 2.8 and 3.0% by weight and optionally between 2.8 and 2.9% by weight. 
     
     
         3 . The sheet according to  claim 1 , the lithium content of which lies between 0.55 and 0.75% by weight and optionally between 0.60 and 0.73% by weight. 
     
     
         4 . The sheet according to  claim 1 , the silver content of which lies between 0.2 and 0.3% by weight. 
     
     
         5 . The sheet according to  claim 1 , the magnesium content of which lies between 0.25 and 0.50% by weight and optionally between 0.30 and 0.45% by weight. 
     
     
         6 . The sheet according to  claim 1  for which the aging is performed at “peak”. 
     
     
         7 . The sheet according to  claim 1 , with thickness between 0.5 and 3 3 mm and having the following properties
 a fracture toughness in plane strain K app , measured on test pieces of type CCT760 (2ao=253 mm), in the L-T direction of at least 120 MPa√m and   a fracture toughness in plane strain K app , measured on test pieces of type CCT1220 (2ao=253 mm), in the L-T direction of at least 120 MPa√m.   
     
     
         8 . The sheet according to  claim 7 , the granular structure of which is essentially recrystallized and having the following properties
 a fracture toughness in plane strain Kapp, measured on test pieces of type CCT760 (2ao=253 mm), in the L-T direction of at least 140 MPa√m and   a fracture toughness in plane strain Kapp, measured on test pieces of type CCT1220 (2ao=253 mm), in the L-T direction of at least 150 MPa√m.   
     
     
         9 . The sheet according to  claim 1 , with thickness between 3.4 and 6 mm and having the following properties
 a fracture toughness in plane strain K app , measured on test pieces of type CCT760 (2ao=253 mm), in the L-T direction of at least 150 MPa√m and optionally at least 155 MPa√m and   a fracture toughness in plane strain K app , measured on test pieces of type CCT1220 (2ao=253 mm), in the L-T direction of at least 170 MPa√m and optionally at least 180 MPa√m.   
     
     
         10 . The sheet according to  claim 1 , with thickness between 3.4 and 8 mm and optionally between 4 and 8 mm and the granular structure of which is essentially unrecrystallized. 
     
     
         11 . A method of manufacturing a sheet according to  claim 1  of thickness of 0.5 to 8 mm made of an aluminum based alloy composition, said method comprising, successively
 a) a molten metal bath is prepared comprising
 2.6 to 3.0% by weight of Cu, 
 0.5 to 0.8% by weight of Li, 
 0.1 to 0.4% by weight of Ag, 
 0.2 to 0.7% by weight of Mg, 
 0.06 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 0.2% by weight, a quantity of Fe and Si less than or equal to 0.1% by weight each, and inevitable impurities having a content less than or equal to 0.05% by weight each and 0.15% by weight in total, 
 
 b) a slab is cast from said molten metal bath; 
 c) said slab is homogenized at a temperature between 450° C. and 535° C.; 
 d) said slab is hot rolled and optionally cold rolled into a sheet of thickness between 0 5 mm and 8 mm; 
 e) said sheet is solution heat treated at a temperature of between 450° C. and 535° C. and quenched; 
 h) said sheet undergoes controlled stretching with a permanent deformation of 0.5 to 5%, total cold working after solution heat treatment and quenching being less than 15%; 
 i) aging is performed comprising heating to a temperature between 130° C. and 170° C. and optionally between 150° C. and 160° C. for 5 to 100 hours and optionally from 10 to 40 hours, the composition and aging being combined so that the yield stress in the longitudinal direction R p0.2 (L) is between 395 and 435 MPa. 
 
     
     
         12 . A sheet according to  claim 1  shaped into an aircraft fuselage panel.