Structure and Hardness of Friction Stir Welds out of High-Strength Non-Heat Hardenable Cast and Wrought Aluminum Alloys

Optical and electron microscopy analyses of friction stir welds out of commercial cast and deformable Al-Mg-x alloys have shown the typical onion-like macrostructure consisting of alternating layers of both the alloys. Maximum microhardness of ~120 Hv has been found in the center of the welds owing to strong grain refinement and exceeding values for both the initial alloys. Mechanisms of structure transformations, as well as hardness changes in the nugget and thermo-mechanically affected zones are discussed.