Method of preparation prior to the welding of lithium-aluminium alloy products

Abstract

The present invention relates to aluminum-lithium alloys in general and, in particular, such products as used in the aircraft industry and the welding of these.

1 . Process for preparing an aluminum lithium alloy product to be fusion-welded comprising:
 (i) procuring a hot-worked aluminum alloy product including at least 0.8% of lithium by weight,   (ii) optionally cold-working the product so obtained,   (iii) cleaning at least one surface to be welded of the product so obtained,   (iv) covering at least one cleaned surface of the product so obtained with a coating whose characteristics when dry are a quantity ranging from 0.1 to 5 mg/cm 2  and a fluorine concentration of at least 10% by weight,   (v) performing a solution heat-treatment at a temperature greater than approximately 450° C. followed by quenching of the product so obtained.   
     
     
         2 . Process according to the  claim 1  in which said aluminum lithium alloy comprises at least 1.4% of lithium by weight. 
     
     
         3 . Process according to  claim 2  in which said aluminum lithium alloy is selected from the group consisting of alloys 2090, 2091, 2196, 2097, 2197, 2297, 2397, 2099, 2199, 8090, 8091, and 8093. 
     
     
         4 . Process according to  claim 1  in which the hot-worked and optionally cold-worked product is a flat-rolled or extruded product with thickness lower than 5 mm. 
     
     
         5 . Process according to  claim 1  in which the cleaning of (iii) is carried out by treating with an aqueous solution with a pH greater than 9. 
     
     
         6 . Process according to  claim 1  in which (iii) and (iv) are carried out on the majority of, or optionally on the whole, surface of said product. 
     
     
         7 . Process according to  claim 1  in which said coating comprises a binder whose concentration when dry ranges from 5% to 50% by weight. 
     
     
         8 . Process according to  claim 1  in which said coating comprises when dry, as a percentage by weight, from 75% to 95% of NaBF4, from 0 to 15% by weight of carboxymethyl cellulose and from 0 to 15% of a silane. 
     
     
         9 . Process according to  claim 1  in which said coating comprises after drying, as a percentage by weight, from 50% to 100% of KxAlyFz, from 0 to 5% by weight of CsxAlyFz and from 0 to 50% of a binder. 
     
     
         10 . Process according to  claim 9  in which said binder is an alkyl silicone resin. 
     
     
         11 . Process according to  claim 9  in which said coating is deposited by electrostatic powdering. 
     
     
         12 . Fusion-welded assembly between a first aluminum alloy member comprising at least 1.4% of lithium by weight and at least one second metal alloy member, said first member being a flat-rolled or extruded product of a thickness less than 5 mm, the first member having been prepared by the process according to  claim 1  wherein a weld between said members is substantially free from porosities. 
     
     
         13 . Welded assembly according to  claim 12  in which the thickness tolerance of said first member is plus or minus 0.20 mm. 
     
     
         14 . Welded assembly according to  claim 12  including at least one second aluminum alloy member including at least 0.8% of lithium by weight. 
     
     
         15 . Welded assembly according to  claim 12  in which said first member is an extruded section and said second member is a sheet or an extruded section. 
     
     
         16 . Fuselage panel including a welded assembly according to  claim 14 . 
     
     
         17 . Welded assembly according to  claim 12  in which the thickness tolerance of said first member is plus or minus 0.15 mm. 
     
     
         18 . Welded assembly according to  claim 12  in which the thickness tolerance of said first member is plus or minus 0.10 mm. 
     
     
         19 . Welded assembly of  claim 12 , wherein said first member comprises a flat-rolled or extruded product of a thickness less than 2 mm.