Investigation of the microstructure and mechanical properties of Mg-Al-Zn alloy joints formed by different laser welding processes

The microstructure and mechanical properties of Mg-Al-Zn alloy joints by using autogenous laser beam welding (LBW) and laser-MIG hybrid welding, respectively, are investigated. The results show that the weld formation of the hybrid welding joint is relatively good, and there are mainly alpha-Mg matrix phases and beta-Mg17Al12 strengthening phases in the weld metal. The microstructure in the fusion zone (FZ) of the two joints is different. The LBW joint is composed of columnar crystal and equiaxed dendrite. The hybrid welding joint consists of fine equiaxed grains, and the grain size in the laser zone is larger than that in the arc zone. The microhardness in FZ is higher due to the precipitation of the beta-Mg17Al12 phase in this region. Under the optimized welding procedure, the strength coefficient of the two joints is >90%. There are many dimples on the tensile fracture surface of the hybrid welding joint, which is characterized by the pattern of the ductile fracture.