Microstructure evolution and mechanical properties of friction stir welded dissimilar joints of Mg-Zn-Gd and Mg-Al-Zn alloys

Friction stir welding (FSW) of dissimilar welds between ZG61 alloy and AZ91D alloy was investigated. Severe deformation and metal flow occur in the stir zone under high strain rates and high temperatures. No distinct reaction layer or intermetallic compounds are observed at the interface of two alloys. When AZ91D was arranged in the advancing side and ZG61 in the retreating side, the joints quality was very poor with all parameters. Microstructure and texture evolution during the FSW and relationship of microstructure, texture and mechanical properties are discussed. The tensile properties of the weld of joints are significantly influenced by the materials positions, grain size and crystallographic orientation. Materials positions and plasticity of base metals is of importance during the FSW of dissimilar alloys. It can be seen that defects cannot be avoided when the heat input were too low to make the metal flow.