Friction stir welding of a commercial 7075-T6 aluminum alloy: Grain refinement, thermal stability and tensile properties

Commercial 7075-T6 aluminum alloy was subjected to friction stir welding (FSW), resulting in development of a fine-grained structure with average size of about 3 pm in the nugget zone. Static annealing at temperatures ranging from 623 to 773 K for 30 min showed that the fine-grain microstructure was stable at temperatures not higher than 723 K. Increase in annealing temperature up to 773 K led to an abnormal grains growth, followed by the development of mm-scale grains. The specimens obtained from the nugget zone demonstrated a superplastic behavior at temperatures ranging from 623 to 723 K and at strain rates ranging from I X 10(-4) to I X 10(-2) s(-1). Large elongation of about 440% was observed at a temperature of 673 K and at a strain rate of I x 10(-3) s(-1).