Characterization of newly developed friction stir-arc welding method for AM60/AZ31 dissimilar Mg alloy

Abstract

The dissimilar AM60/AZ31 Mg alloys joints were obtained via friction stir welding (FSW). Then, the upper and lower surfaces of the FSW joint were remelted by using tungsten inert gas (TIG) welding. The macrostructures, microstructure evolution and mechanical properties of the two kinds of joints were investigated. The results indicated that there was a TIG weld zone in both the upper and lower parts of the nugget zone (NZ) of the FSW joint after the arc heating. Further, the grain size in the NZ-middle grew to a certain extent, especially the area near the NZ-middle-center. Texture analysis showed that the texture in the NZ-middle was modified after the arc heating, especially in the TIG weld zones. However, there were no significant changes in texture and grain size near the NZ interface. The tensile results showed that the tensile strength and yield strength of the two joints were similar, but the joint elongation after arc heating was largely improved, by about 57%. The equivalent strength of the two kinds of joints was due to the similar texture and grain size near their NZ interfaces. The higher elongation was attributed to the increase of the Schmid factor values (basal slip and extension twinning) caused by the weakening of the texture, the growth of the grain size and the annihilation of the initial residual dislocation in the NZ-middle. As a result, the difficulty of deformation in the NZ-middle was reduced, which weakened the localized strain of the joint. This work could provide a new method for weakening the strain localization of FSW Mg joints.