Microstructure and Mechanical properties of Mg96Zn2Y2 joints welded by resistance spot welding

Mg96Zn2Y2 is widely studied due to its high tensile yield strength and elongation. These excellent properties were considered to relate to the nanostructure of the alloy such as fine-grained alpha-Mg matrix and bent long period stacking ordered (LPSO) structure. In order to extend the application of this Mg alloy, development of the welding technique is indispensable. In the light of the reliability and productivity, resistance spot welding is an attractive method to join this Mg alloy. In this study, we joined the Mg alloys by the resistance spot welding with cover plates. Mechanical properties and structures of the nugget of the joints were investigated. In the case of the joints welded with cover plates, the welded region of the Mg alloy sheets were covered with steel plates to supply adequate heat for welding. Joints of extruded Mg96Zn2Y2 were obtained at relatively low welding current. The tensile strength of Mg96Zn2Y2 alloy was higher than that of the commercial Mg alloy AZ318 joints. Mg96Zn2Y2 base alloy had extended LPSO phase along extruded direction in alpha-Mg grains. At the nugget, net-like secondary phase was produced in the Mg grains. The relationship between the microstructure in the joints and mechanical properties were discussed.