Method for manufacturing products made of magnesium-lithium-aluminum alloy

Abstract

The invention relates to a method for manufacturing a wrought product. The invention further provides, a wrought product able to be obtained according to the method of the invention as well as the use of said wrought product to produce aircraft structural elements.

1 . Method for manufacturing a wrought product wherein:
 (a) an unprocessed form of aluminum alloy is cast, which has the composition, in % by weight: Mg: 4.0-5.0; Li: 1.0-1.8; Zr: 0.05-0.15; Mn: ≦0.6; Ag: ≦0.5; Fe: ≦0.1; Ti: <0.15; Si: ≦0.05; other elements ≦0.05 each and ≦0.15 in association; the remainder is aluminum;   (b) optionally, said unprocessed form is homogenized;   (c) said unprocessed form is hot worked to obtain a hot-worked product;   (d) optionally, said hot-worked product is solution heat treated at a temperature from 360° C. to 460° C., optionally from 380 to 420° C., for 15 minutes to 8 hours;   (e) said hot-worked product is quenched;   (f) optionally, said hot-worked and quenched product is straightened or flattened;   (g) said hot-worked and quenched product is artificially aged;   (h) the aged as such worked product is cold worked under controlled conditions to obtain permanent cold working set in stretching from 1 to 10%, optionally from 2 to 6%, optionally from 3 to 5%.   
     
     
         2 . Method according to  claim 1  wherein the hot working of (c) is a working by extrusion of the unprocessed form. 
     
     
         3 . Method according to  claim 1  wherein the hot working of (c) is carried out at an initial temperature greater than 400° C., optionally from 420° C. to 450° C. 
     
     
         4 . Method according to  claim 1  wherein the quenching of the (e) is a press quenching. 
     
     
         5 . Method according to  claim 1  wherein the quenching of the (e) is carried out with air. 
     
     
         6 . Method according to  claim 1  wherein the artificial aging of the product hot worked and quenched in (g) is carried out by heating, in one or several steps, at a temperature less than 150° C., optionally at a temperature from 70° C. to 140° C., for 5 to 100 hours. 
     
     
         7 . Method according to  claim 1  wherein said unprocessed form made of aluminum alloy has a Mn content, in % by weight, from 0.2 to 0.6, optionally from 0.35 to 0.5. 
     
     
         8 . Method according to  claim 1  wherein said unprocessed form made of aluminum alloy has a Zn content, in % by weight, less than 0.04%, optionally less than or equal to 0.03%. 
     
     
         9 . Method according to  claim 1  wherein said unprocessed form made of aluminum alloy has an Fe content, in % by weight, less than 0.08%, optionally less than or equal to 0.07%, optionally less than or equal to 0.06%. 
     
     
         10 . Method according to  claim 1  wherein said unprocessed form made of aluminum alloy has a Li content, in % by weight, less than 1.6%, optionally less than or equal to 1.5%, optionally less than or equal to 1.4%. 
     
     
         11 . Wrought product able to be obtained according to a method of  claim 1 . 
     
     
         12 . Wrought product according to  claim 11  having at mid-thickness, for a thickness between 0.5 and 15 mm, at least one static mechanical resistance property among the properties (i) to (iii) and at least one damage tolerance property among the properties (iv) to (v):
 (i) an ultimate tensile strength, Rm (L)≧440 MPa, optionally Rm (L)≧445 MPa and, optionally, Rm (L)≧450 MPa; 
 (ii) a tensile yield strength Rp0.2 (L)≧360 MPa and optionally Rp0.2 (L)≧380 MPa and, optionally, Rp0.2 (L)≧400 MPa; 
 (iii) a tensile yield strength Rp0.2 (TL)≧330 MPa and optionally Rp0.2 (TL)≧340 MPa and, optionally, Rp0.2 (TL)≧370 MPa; 
 (iv) a toughness, measured according to standard ASTM E399 with specimens CT8 of width W=16 mm and of thickness=8 mm, KQ (L-T) 20 MPa√m, optionally KQ (L-T)≧22 MPa√m; 
 (v) a stress intensity factor corresponding to the maximum force Pmax, measured according to standard ASTM E399 with specimens CT8 of width W=16 mm and of thickness=8 mm, Kmax (L-T)≧20 MPa√m, optionally Kmax (L-T)≧25 MPa√m. 
 
     
     
         13 . A wrought product obtained according to a method of  claim 1  that is used in an aircraft structural element, optionally a fuselage skin, a circumferential frame, a fuselage stiffener or stringer or a wing skin, a wing stiffener, a rib or a spar.