Microstructure homogeneity and mechanical properties of laser-arc hybrid welded AZ31B magnesium alloy

Laser-arc hybrid welding of AZ31B magnesium alloy was carried out, the effects of welding parameters on weld formation, microstructure homogeneity and mechanical properties were investigated. The results showed that laser-arc hybrid welding was beneficial to improve the weld formation of magnesium alloy by inhibiting the defect of undercut and pores. The weld microstructure was mainly columnar grains neighboring the fusion line and equiaxed grains at the weld center. It was interesting that the grain size at the upper arc zone was smaller than that at the lower laser zone, with the difference mainly affected by laser power rather than welding current and welding speed. The welding parameters were optimized as laser power of 3.5 kW, welding current of 100 A and welding speed of 1.5 m/min. In this case, the weld was free of undercut and pores, and the tensile strength and elongation rate reached 252 MPa and 11.2%, respectively. Finally, the microstructure homogeneity was illustrated according to the heat distribution, and the evolution law of tensile properties was discussed basing on the weld formation and microstructure characteristics.