Microstructures and mechanical properties of ZK40 high strength magnesium alloy joints by CO_2 laser beam welding

The as-rolled ZK40 magnesium alloy sheets were joined by laser beam welding. The effects of welding parameters on the microstructures and mechanical properties of the joints were studied. The results show that a sound bead, with the ultimate tensile strength of 315 MPa, up to 91.3% of that of base metal, can be obtained with the optimized welding parameters. No columnar grains can be found at the fusion boundary, and the fusion zone (FZ) is characteristic of equiaxed dendritic grains and fine Mg51Zn20 precipitates disperse along the grain boundaries and among the dendritic arms. With the heat input increasing, the grains in FZ get coarser and more dendritic.