Tensile properties of AZ61 magnesium alloy produced by multi-pass friction stir processing: Effect of sample orientation

AZ61 magnesium alloy plate was prepared by multi-pass friction stir processing (M-FSP) with an overlapping ratio of 50%, and the microstructures and tensile properties of the M-FSP plate were studied with the tensile samples oriented in the processing direction (PD), transverse direction (TD) and 45° to the PD. The large-scale M-FSP AZ61 alloy plate was observed to be free of macro-defects. The grain size of as-cast AZ61 plate was significantly refined through FSP due to the presence of dynamic recrystallization. The subsequent passes could further refine the grain size of stir zones, while the periodic transition zones with non-uniform microstructures were present in the plate. Compared with the as-cast plate, an effective improvement in both strength and ductility was achieved in the M-FSP magnesium plate in both PD and TD because of the grain refinement and the elimination of cast defects. While the ductility was lower in the samples oriented along 45° to the PD, the strength was also higher than that of the as-cast plate. The orientation dependence of the tensile properties of M-FSP AZ61 magnesium plate was mainly attributed to the local non-uniform microstructure and texture.