Effects of Welding Speed and Post-weld Hot Rolling on Microstructure and Mechanical Properties of Friction Stir-Welded AZ31 Magnesium Alloy

The as-rolled AZ31 Mg alloy sheets are welded by friction stir welding (FSW) in this study, followed by annealing and hot rolling with different reductions. The effects of welding speed and the rolling reduction on the microstructure, tensile properties, microhardness and fracture surfaces of the specimens are investigated. The results show that the microstructures of the FSW joint in different regions become more and more consistent as the hot rolling reduction increases. The mechanical properties of the FSW joints and the joint coefficient are improved with increasing rolling reduction; however, the hardness value in the stirred zone decreases firstly and then increases. When the rolling reduction is 50%, the tensile strength of FSW joint is close to that of base metal. The sample L-3 achieves the best comprehensive properties, with the yield strength, ultimate tensile strength and elongation of 162, 287.9 MPa, and 17.9%, respectively.