Abnormal Grain Growth Suppression in AL Alloys

Abstract

The present invention provides a process for suppressing abnormal grain growth in friction stir welded aluminum alloys by inserting an intermediate annealing treatment (“IAT”) after the welding step on the article. The IAT may be followed by a solution heat treatment (SHT) on the article under effectively high solution heat treatment conditions. In at least some embodiments, a deformation step is conducted on the article under effective spin-forming deformation conditions or under effective superplastic deformation conditions. The invention further provides a welded article having suppressed abnormal grain growth, prepared by the process above. Preferably the article is characterized with greater than about 90% reduction in area fraction abnormal grain growth in any friction-stir-welded nugget.

1 . A welded article having good strength and ductility because of fine grain microstructure based upon significantly suppressed abnormal grain growth, prepared by a process comprising:
 (a) providing an article comprising an aluminum alloy;   (b) friction-stir-welding the article under effective friction-stir-welding conditions;   (c) inserting an intermediate annealing treatment (“IAT”) after the welding step on the article under effective intermediate annealing conditions comprising an effective time period and an IAT temperature lower than a solidus line on a phase diagram for the aluminum alloy;   (d) conducting solution heat treatment on the article under effective solution heat treatment conditions; and   (e) recovering the article characterized with greater than about 90% reduction in area fraction abnormal grain growth in any friction-stir-welded nugget.   
     
     
         2 . The article of  claim 1 , further prepared by the step comprising conducting deformation on the article under effective spin-forming deformation conditions or under effective superplastic deformation conditions. 
     
     
         3 . The article of  claim 1 , wherein the aluminum alloy is selected from the group consisting of 2xxx series, 7xxxx series, and combinations thereof. 
     
     
         4 . The article of  claim 3 , wherein the aluminum alloy is 2xxx series. 
     
     
         5 . The article of  claim 4 , wherein the aluminum alloy is 2195 and is recovered with a high strength temper selected from the group consisting of T6 and T8.