Aluminum copper lithium alloy with improved mechanical strength and toughness

Abstract

The invention is a rolled and/or forged product, made of an aluminium-based alloy comprising, in % by weight, Cu: 3.2-4.0; Li: 0.80-0.95; Zn: 0.45-0.70; Mg: 0.15-0.7; Zr: 0.07-0.15; Mn: 0.1-0.6; Ag:<0.15; Fe+Si≤0.20; at least one element from Ti: 0.01-0.15; Se: 0.02-0.1; Cr: 0.02-0.1; Hf: 0.02-0.5; V: 0.02-0.1; other elements ≤0.05 each and ≤0.15 in total, remainder aluminium. In the process for manufacturing the products according to the invention a bath of liquid metal based on aluminium as alloy according to the invention is melted, an unwrought product is cast from said bath of liquid metal; said unwrought product is homogenized at a temperature between 450° C. and 550° C.; said unwrought product is hot worked and optionally cold worked preferably to a thickness of at least 15 mm: said product is solution treated between 490° C. and 530° C. for 15 min to 8 h and quenched; said product is drawn in a controlled manner with a permanent deformation of 1% to 7% and a tempering of said product is carried out. The product is advantageous for the manufacture of an aircraft structural component.

1 . Rolled and/or forged aluminum-based alloy product comprising the following % by weight,
 Cu: 3.2-4.0;   Li: 0.80-0.95;   Zn: 0.45-0.70;   Mg: 0.15-0.7;   Zr: 0.07-0.15;   Mn: 0.1-0.6;   Ag: <0.15;   Fe+Si≤0.20;   at least one element from among   Ti: 0.01-0.15;   Sc: 0.02-0.15, optionally 0.02-0.1;   Cr: 0.02-0.3, optionally 0.02-0.1;   Hf: 0.02-0.5;   V: 0.02-0.3, optionally 0.02-0.1;   other elements<0.05 each and<0.15 total, remainder aluminum.   
     
     
         2 . Product according to  claim 1 , in which the magnesium content is at most (0.55-5*Ag). 
     
     
         3 . Product according to  claim 1 , in which the copper content is between 3.3 and 3.8%; and optionally between 3.4 and 3.7% by weight. 
     
     
         4 . Product according to  claim 1 , in which the zinc content is between 0.50 and 0.60% by weight. 
     
     
         5 . Product according to  claim 1 , in which the manganese content is between 0.2 and 0.4% by weight. 
     
     
         6 . Product according to  claim 1 , in which the lithium content is between 0.84% and 0.93% by weight, and optionally the lithium content is at least 0.86% by weight. 
     
     
         7 . Product according to  claim 1  for which the thickness is equal to at least 12 mm and optionally at least 40 mm. 
     
     
         8 . Product according to  claim 1  in a rolled and/or forged, solution heat treated, quenched, stress relieved optionally by stretching, and aged temper with at least one of the following pairs of characteristics for thicknesses of between 40 and 75 mm:
 (i) at quarter thickness, yield stress R p0.2 (LT)≤480 MPa and optionally R p0.2 (LT)≤490 MPa and toughness K 1C  (T-L)≤31 MPa√m and advantageously such that K 1C  (T-L)≤−0.175 R p0.2 (LT)+119.2, optionally K 1C  (T-L)≤−0.175 R p0.2 (LT)+120.5 and optionally K 1C  (T-L)≤−0.175 R p0.2 (LT)+121.5, 
 (ii) at mid thickness, yield stress R p0.2 (ST)≤450 MPa and optionally R p0.2 (ST)≤455 MPa and toughness K 1C  (S-L)≤24 MPa√m and advantageously such that K 1C  (S-L)≤−0.34 R p0.2 (ST)+185.6, optionally K 1C  (S-L)≤−0.34 R p0.2 (ST)+187.2 and optionally K 1C  (S-L)≤−0.34 R p0.2 (ST)+188.7, 
 
     
     
         9 . Product according to  claim 1  having, in a rolled and/or forged, solution heat treated, quenched, stress relieved optionally by stretching, and aged temper, at least one of the following pairs of characteristics for thicknesses of between 40 and 150 mm, the toughness in plane stress K app  being measured on test pieces type CCT406 (2ao=101.6 mm)
 (i) for thicknesses of between 40 and 75 mm K app , in the L-T direction of at least 105 MPa √m and optionally at least 110 MPa √m and a yield stress R p0.2  (L) equal to at least 500 MPa and optionally at least 510 MPa, 
 (ii) for thicknesses of between 40 and 75 mm K app , in the T-L direction of at least 60 MPa √m and optionally at least 70 MPa √m and a yield stress R p0.2 (LT) equal to at least 480 MPa and optionally at least 490 MPa. 
 (iii) for thicknesses of between 76 and 120 mm K app , in the L-T direction of at least 80 MPa √m and optionally at least 90 MPa √m and a yield stress R p0.2 (L) equal to at least 475 MPa and optionally at least 485 MPa, 
 (iv) for thicknesses of between 76 and 120 mm K app , in the T-L direction of at least 40 MPa √m and optionally at least 50 MPa √m and a yield stress R p0.2 (LT) equal to at least 455 MPa and optionally at least 465 MPa. 
 (v) for thicknesses of between 121 and 150 mm K app , in the L-T direction of at least 75 MPa √m and optionally at least 80 MPa √m and a yield stress R p0.2 (L) equal to at least 470 MPa and optionally at least 480 MPa, 
 (vi) for thicknesses of between 121 and 150 mm K app , in the T-L direction of at least 40 MPa √m and optionally at least 45 MPa √m and a yield stress R p0.2 (LT) equal to at least 445 MPa and optionally at least 455 MPa. 
 
     
     
         10 . Product according to  claim 1 , in which the magnesium content is at least 0.34% by weight, and the silver content is less than 0.05% by weight. 
     
     
         11 . Product according to  claim 10  in a rolled and/or forged, solution heat treated, quenched, stress relieved optionally by stretching, and aged temper, with at least one of the following pairs of characteristics for thicknesses of between 76 and 150 mm:
 (i) for thicknesses of 76 to 120 mm, at quarter thickness, yield stress R p0.2 (LT)≤460 MPa and optionally R p0.2 (LT)≤470 MPa and a toughness K 1C  (T-L)≤27 MPa√m and advantageously such that K 1C  (T-L)≤−0.1 R p0.2 (LT)+77, optionally K 1C  (T-L)≤−0.1 R p0.2 (LT)+78 and optionally K 1C  (T-L)≤−0.1 R p0.2 (LT)+79, 
 (ii) for thicknesses of 76 to 120 mm, at mid thickness, yield stress R p0.2 (ST)≤435 MPa and optionally R p0.2 (ST)≤445 MPa and toughness K 1C  (S-L)≤23 MPa√m and advantageously such that K 1C  (S-L)≤−0.25 R p0.2  (ST)+139.25, optionally K 1C  (S-L)≤−0.25 R p0.2 (ST)+140.85 and optionally K 1C  (S-L)≤−0.25 R p0.2 (ST)+142.45, 
 (iii) for thicknesses of 121 to 150 mm, at mid thickness, yield stress R p0.2 (ST)≤420 MPa and optionally R p0.2 (ST)≤425 MPa and toughness K 1C  (S-L)≤20 MPa√m and advantageously such that K 1C  (S-L)≤−0.25 R p0.2 (ST)+133, optionally K 1C  (S-L)≤−0.25 R p0.2 (ST)+133 and optionally K 1C  (S-L)≤−0.25 R p0.2 (ST)+134, 
 
     
     
         12 . Product according to  claim 1  in a rolled and/or forged, solution heat treated, quenched, stress relieved optionally by stretching, and aged temper, for which the number of days before failure tested according to ASTM standards G47 and G49 at mid-thickness for a stress in the ST direction equal to 350 MPa is at least 30 days and optionally, for plates between 40 and 75 mm thick, the number of days before failure for a stress of 450 MPa in the ST direction is at least 30 days. 
     
     
         13 . Method of manufacturing a rolled and/or forged product based on an aluminum alloy, in which
 a) a bath of liquid metal is created based on an aluminum alloy according to  claim 1 ;   b) an unwrought product is cast from said liquid metal bath;   c) said unwrought product is homogenized at a temperature of between 450° C. and 550°, and optionally between 480° C. and 530° C. for a duration of between 5 and 60 hours;   d) said unwrought product is hot and optionally cold worked optionally to a thickness of at least 12 mm, optionally at least 15 mm, and optionally at least 40 mm into a rolled and/or forged product;   e) said product is solution heat treated at between 490 and 530° C. for 15 minutes to 8 h and is quenched;   f) said product is stress relieved, optionally by stretching, in a controlled manner, with a permanent set of 1 to 7% and optionally at least 4%;   g) said product is aged including heating to a temperature of between 130 and 170° C., optionally between 140 and 160° C., and optionally between 140 and 150° C., for 5 to 100 hours and optionally 10 to 50 h.   
     
     
         14 . Method according to  claim 13 , in which the controlled stretching is applied with a permanent set of between 5 and 7% and the ageing time is between 10 and 30 hours. 
     
     
         15 . Structural element of an aircraft, optionally the lower wing skin or upper wing skin element in which the skin and the stiffeners are made from the same initial product, a spar or a rib, comprising a product according to  claim 1 .