Aluminum magnesium lithium alloy with improved fracture toughness

Abstract

Wrought product made of aluminum alloy composed as follows, as a percentage by weight Mg: 4.0-5.0; Li: 1.0-1.6; Zr: 0.05-0.15; Ti: 0.01-0.15; Fe: 0.02-0.2; Si: 0.02-0.2; Mn: ≦0.5; Cr≦0.5; Ag: ≦0.5; Cu≦0.5; Zn≦0.5; Sc≦0.01; other elements <0.05; the rest aluminum.

1 . A wrought product comprising an aluminum alloy of a composition, as a percentage by weight,
 Mg: 4.0-5.0   Li: 1.0-1.6   Zr: 0.05-0.15   Ti: 0.01-0.15   Fe: 0.02-0.2   Si: 0.02-0.2   Mn: ≦0.5   Cr ≦0.5   Ag: ≦0.5   Cu ≦0.5   Zn ≦0.5   Sc <0.01   other elements <0.05, each   remainder aluminum;   
     
     
         2 . A wrought product according to  claim 1 , comprising at least one element selected from the group consisting of Mn and Cr with the following contents if chosen, as a percentage by weight
 Mn: 0.05-0.5   Cr: 0.05-0.3, and   an element not chosen from among Mn and Cr having a content less than 0.05% by weight.   
     
     
         3 . The wrought product according to  claim 1 , comprising at least one element selected from the group consisting of Cu and Ag with the following contents if chosen, as a percentage by weight
 Cu: 0.05-0.3   Ag: 0.05-0.3, and   an element not chosen from among Cu and Ag having a content less than 0.05% by weight.   
     
     
         4 . The wrought product according to  claim 1 ,wherein the Li content is, as a percentage by weight
 Li: 1.1-1.5.and optionally Li: 1.2-1.4.   
     
     
         5 . The wrought product according to  claim 1 , wherein the Mg content is, as a percentage by weight
 Mg: 4.4-4.7.   
     
     
         6 . The wrought product according to  claim 1 , comprising a maximum Be content of 5 ppm and/or a maximum Na content of 10 ppm and/or a maximum Ca content of 20 ppm. 
     
     
         7 . The wrought product according to  claim 1 , comprising a Zn content less than 0.2% by weight and optionally less than 0.05% by weight. 
     
     
         8 . The wrought product according to  claim 1 , wherein said Fe content and/or said Si content are, as a percentage by weight
 Fe: 0.04-0.15   Si: 0.04-0.15.   
     
     
         9 . The wrought product according to  claim 1 , wherein said product has been worked and the working is carried out by rolling. 
     
     
         10 . The wrought product according to  claim 9 , comprising a thickness ranging from 0.5 to 15 mm, at mid-thickness having at least one static mechanical strength property among properties (i) to (iii) and at least one damage tolerance property among properties (iv) to (vi)
 (i) a tensile yield stress R p0.2 (L)≧280 MPa and optionally R p0.2 (L)≧310 MPa,   (ii) a tensile yield stress R p0.2 (LT)≧260 MPa and optionally R p0.2 (LT)≧290 MPa,   (iii) a tensile yield stress R p0.2 (45°)≧200 MPa and optionally R p0.2 (45°)≧240 MPa,   (iv) a fracture toughness for test-specimens of width W=760 mm K app  (L-T)≧90 MPa√m for a thickness less than 3 mm and K app  (L-T)≧110 MPa√m for a thickness of at least 3 mm,   (v) a fracture toughness for test-specimens of width W=760 mm K app  (T-L)≧100 MPa√m for a thickness less than 3 mm and K app  (T-L)≧120 MPa√m for a thickness of at least 3 mm,   (vi) a crack extension of the last valid point of R curve for test-specimens of width W=760 mm Δa eff(max)  (T-L)≧80 mm for a thickness of less than 3 mm and Δa eff(max)  (T-L)≧110 mm for a thickness of at least 3 mm.   
     
     
         11 . The manufacturing process for a wrought product according to  claim 1 , comprising:
 preparing a molten metal bath in order to obtain an aluminum alloy,   casting said alloy in a rough shape to form a cast product,   optionally homogenizing of the cast product,   hot and optionally cold working said product,   optionally heat treating the product at a temperature ranging from 300 to 420° C. in at least one step,   solution heat-treating the product so worked, and quenching,   optionally cold working the product that has been solution heat treated and quenched,   conducting artificial aging at a temperature of not more than 150° C.   
     
     
         12 . The process according to  claim 11 , wherein said quenching is carried out in air. 
     
     
         13 . The product according to  claim 1 , capable of being used to produce an aircraft structural element, optionally a fuselage skin, a fuselage framework, a stringer or a rib. 
     
     
         14 . The process of  claim 11 , which is conducted in the order given. 
     
     
         15 . The process of  claim 11 , wherein working is conducted by rolling.