On the effect of Zn, Cu, and brass interlayers in friction stir welded St37 and AZ31 dissimilar joints

In this research, dissimilar friction stir welding of AZ31 magnesium alloy and St37 steel sheets was performed to investigate the effect of Zn, Cu, and brass interlayers on the microstructure and mechanical properties of the joint. After conducting microstructural and mechanical evaluations, welding with a Zn interlayer exhibited the best strength and bonding efficiency, achieving 161 MPa and 60%, respectively. Since mechanical and metallurgical bonding at the interface plays a complementary role in improving welding properties, the presence of the Zn interlayer, by deoxidizing and enhancing reactions at the interface, increases the thickness of the Fe-Al-based intermetallic compound layer from 110 nm in welding without an interlayer to 300 nm. This results in improved mechanical properties of the welds. Examination of the fracture surfaces from the tensile test samples shows that all samples exhibit brittle fracture, except for the sample with the Zn interlayer, which displays a combination of ductile and brittle fracture.