Effect of Multi-pass Submerged Friction Stir Processing on Microstructure Evolution and Mechanical Properties of AZ61 Magnesium Plate

In this work, the effect of multi-pass submerged friction stir processing (MSFSP) on a casting AZ61 Mg plate was investigated. AZ61 plate was successfully prepared by repeating the processing with the subsequent pass FSP overlapped the retreating side with an overlapping ratio of 50%. The microstructure and resulting mechanical properties at room temperature were studied. The results revealed that the fine and equiaxed grains with an average grain size of 10.7 μm obtained in stirring zone (SZ) through MSFSP, and the second-phase Mg17Al12 was broken into small particles. Compared to BM, MSFSP specimens achieved an improvement in microhardness, tensile strength and elongation but exhibited obvious mechanical anisotropy, especially the ductility. It is considered that the enhancement in mechanical properties is benefit from grain refinement and the texture evolution may be responsible for the mechanical anisotropy.