Microstructure and mechanical properties of laser welded wrought ZK21 magnesium alloy

The as-rolled ZK21 magnesium alloy sheets of 2 mm in thickness were successfully joined by laser welding. The effects of the welding parameters including the laser power and the welding speed on the microstructure and mechanical properties of the joints were investigated. A sound bead, with the ultimate tensile strength (UTS) of 289 MPa and up to 94% of the base metal, was obtained with the optimized welding parameters. The fusion zone (FZ) was characteristic of equiaxed dendritic grains of about 15 μm in size and fine Mg₂Zn₃ precipitates dispersed among the dendritic arms. Besides, a few columnar grains grew from the fusion boundary epitaxially. The fine grains in the heat-affected zone (HAZ) were ascribed to recrystallization.