Improved thin sheet made of aluminium-copper-lithium alloy

Abstract

The invention relates to a thin sheet, the thickness of which is less than 12.7 mm, having an essentially recrystallized granular structure, made from an aluminum-based alloy comprising 2.5 to 3.5% by weight of Cu, 0.7 to 0.9% by weight of Li, 0.3 to 0.5% by weight of Mg, 0.2 to 0.5 by weight of Mn, 0.25 to 0.65% by weight of Zn, 0.01 to 0.15% by weight of Ti, 0 to 0.07% by weight of Ag, an amount of Fe and of Si of less than or equal to 0.1% by weight each, and inevitable impurities at a content of less than or equal to 0.05% by weight each and 0.15% by weight in total, with the remainder being aluminum.

1 . A thin sheet with a thickness of less than 12.7 mm with an essentially recrystallized granular structure made from an aluminum-based alloy comprising, as % by weight,
 2.5 to 3.5% Cu   0.7 to 0.9% Li   0.3 to 0.5% Mg   0.2 to 0.5% Mn   0.25 to 0.65% Zn   0.01 to 0.15% Ti   0 to 0.07% Ag   
       a quantity of Fe and of Si less than or equal to 0.1% each, and unavoidable impurities in a proportion of less than or equal to 0.05% each and 0.15% in total, the remainder aluminum. 
     
     
         2 . The thin sheet according to  claim 1 , the silver Ag content of which is less than or equal to 0.05% by weight, optionally less than or equal to 0.04% by weight, optionally less than or equal to 0.03% by weight. 
     
     
         3 . The thin sheet according to  claim 1 , the magnesium Mg content of which is between 0.30% and 0.45% by weight. 
     
     
         4 . The thin sheet according to  claim 1 , the lithium Li content of which is between 0.7% and 0.8% by weight, optionally from 0.70 to 0.80% by weight. 
     
     
         5 . The thin sheet according to  claim 1 , the copper Cu content of which is between 2.8 and 3.1% by weight. 
     
     
         6 . The thin sheet according to  claim 1 , the manganese Mn content of which is between 0.20 and 0.45% by weight and optionally from 0.25 to 0.45% by weight. 
     
     
         7 . The thin sheet according to  claim 1 , the zinc Zn content of which is between 0.45% and 0.65% by weight. 
     
     
         8 . The thin sheet according to  claim 1 , having in the T8 temper
 a flat strain toughness Kapp in the L-T direction and in the T-L direction, measured on test pieces of type CCT760 with 2ao precracking equal to 253 mm, of at least 120 MPa m, optionally at least 125 MPa m, optionally 130 MPa m,   a tensile elastic limit R p0.2  in the L direction and in the TL direction of at least 380 MPa, optionally at least 385 MPa,   a valid value of Δaeff max measured in the L-T direction and in the T-L direction on test pieces of type CCT760 with a 2ao pre-cracking equal to 253 mm, of at least 80 mm, optionally 90 mm, optionally 100 mm.   
     
     
         9 . A method for manufacturing a thin sheet with a thickness of less than 12.7 mm, optionally a thickness of between 0.5 and 9 mm, comprising successively
 a) producing a liquid metal bath so as to obtain an aluminum alloy comprising, as % by weight,
 2.5 to 3.5% Cu 
 0.7 to 0.9% Li 
 0.3 to 0.5% Mg 
 0.2 to 0.5% Mn 
 0.25 to 0.65% Zn 
 0.01 to 0.15% Ti 
 0 to 0.07% Ag 
   
       a quantity of Fe and of Si of less than or equal to 0.1% each, and unavoidable impurities in a proportion of less than or equal to 0.05% each and 0.15% in total, the remainder aluminum,
 b) casting a plate from said liquid metal bath, 
 c) homogenizing said plate at a temperature of between 480° C. and 535° C., 
 d) rolling said plate by hot rolling and optionally cold into a sheet having a thickness of less than 12.7 mm, optionally a thickness of 0.5 mm to 9 mm, 
 e) implementing solution heat treatment at a temperature of between 450° C. and 535° C. and quenching of said sheet; 
 f) tractioning said sheet is tractioned in a controlled manner with a permanent deformation of 0.5 to 5%; 
 g) aging comprising heating at a temperature of between 130 and 170° C. and optionally between 150 and 160° C. for 5 to 100 hours and optionally from 10 to 60 hours. 
 
     
     
         10 . The method for manufacturing a thin sheet according to  claim 9  such that the aging implemented at g) has an equivalent duration t1 eq   150°  of between 10 h and 80 h, optionally from 40 h to 75 h, an equivalent duration t1 eq   150°  calculated at the temperature of 150° C. in accordance with the formula 
       
         
           
             
               
                 t 
                 ⁢ 
                 
                   1 
                   eq 
                   
                     150 
                     ⁢ 
                     ° 
                     ⁢ 
                         
                     C 
                   
                 
               
               = 
               
                 
                   ∫ 
                   
                        
                      
                   
                   
                        
                      
                   
                 
                 
                   
                     dt 
                     . 
                     exp 
                   
                   ⁢ 
                   
                     ⌈ 
                     
                       
                         - 
                         
                           13600 
                           8.314 
                         
                       
                       · 
                       
                         ( 
                         
                           
                             1 
                             
                               
                                 
                                   T 
                                   
                                     ° 
                                     ⁢ 
                                         
                                     C 
                                   
                                 
                                 ( 
                                 t 
                                 ) 
                               
                               + 
                               273 
                             
                           
                           - 
                           
                             1 
                             
                               150 
                               + 
                               273 
                             
                           
                         
                         ) 
                       
                     
                     ⌉ 
                   
                 
               
             
           
         
       
       where T° C. (t) (in ° C.) is the instantaneous temperature of the sheet that changes with time (in seconds). 
     
     
         11 . A product for a fuselage structure comprising a sheet according to  claim 1 .