Effect of post-weld heat treatment on mechanical properties of local weld-affected zones in friction stir welded AZ31 plates

This study explored the mechanical, microstructural, and textural characteristics of friction stir welded (FSWed) AZ31 magnesium alloy plates. The joints were subsequently annealed at various temperatures in the range of 300-500 degrees C for 1 h. Reduction in yield strength was found, though simultaneous improvement in tensile strength and elongation was achieved by annealing at 300 degrees C and 400 degrees C. The digital image correlation (DIC) analysis clearly showed a gradual expansion of the strain localized area toward the base material (BM) zone with an increase of the annealing temperature. The texture-dependent Hall-Petch relationship was established and discussed together with the dislocation density. The nanoindentation maps in concert with the kernel average misorientation (KAM) reveal that the difference of dislocation density in stir zone (SZ), thermo-mechanically affected zone (TMAZ), and BM zone is responsible for different grain growth trends which links to the improvement in mechanical properties.