Grain refinement process in commercial 7075-T6 aluminum alloy under friction stir welding and superplasticity

Process of grain refinement taking place during friction stir welding of a 7075-T6 Al alloy was studied. It appears that the fine-grained structure is formed by the grain fragmentation process, i.e., grains split by the development of internal boundaries with medium to high angle misorientations, mainly caused by dynamic recrystallization, followed by the evolution of new fine grains. The fine-grained alloy shows superplasticity at around 673K at strain-rate of 1 x 10(-3)s(-1).