Microstructure and mechanical properties of the laser-welded Mg-3Nd-0.2Zn-0.4Zr (NZ30K) magnesium alloy

4 mm thick Mg-3Nd-0.2Zn-0.4Zr (NZ30K) and AZ31 magnesium alloy plates were laser beam welded. The microstructures of NZ30K and AZ31 joints were compared and the distribution of Nd in NZ30K was emphatically investigated. Besides, microhardness distributions and tensile properties at room temperature and high temperature (200 °C) of NZ30K and AZ31 joints were tested and fracture features were observed and analyzed. The results indicate that NZ30K rare-earth magnesium alloy shows better properties especially at high temperature (200 °C) benefitting from the strengthening phase than AZ31 joints. Microhardness in fusion zone of NZ30K changes a little compared to that in base metal, while microhardness in fusion zone of AZ31 decreases a lot. The grain of NZ30K in fusion zone is significantly refined with strengthening phase distributing on grain boundary. Tensile strength of NZ30K laser beam welded joints at high temperature (200 °C) decreases by 29% compared to that at room temperature, while tensile strength of AZ31 joint at high temperature (200 °C) decreases by 53% compared to that at room temperature, which is mainly because of the stable existence of the strengthening phase Mg12Nd in NZ30K rare-earth magnesium alloy while the strengthening phase Mg17Al12 in AZ31 would soften and coarsen with the temperature going up.84