Effects of Cu-Zn alloy additions on microstructure and strength of welded joints between magnesium alloy and mild steel

Experimental investigations on lap welding of magnesium alloy to steel using resistance spot welding with Cu-Zn alloy interlayer are carried out. The effect of welding time, welding current and interlayer thickness on the bonding mode of interface and joint strength has been investigated using mechanical testing and metallurgical examination. The results show that the strength of Mg-steel joints without an interlayer could reach 30 MPa by the optimization of welding current and time. The addition of alloy elements, realized by adjustment of interlayer thickness, has a noticeable effect on mechanical properties and microstructure of the joints. Particularly, with the addition of Cu-Zn interlayer (0.1 mm in thickness), the tensile strength could attain 62 MPa. Owning to the addition of the Cu-Zn alloy interlayer, a metallurgical bonding between Mg alloy and steel is achieved based on the formation of intermetallic compounds of CuMgZn and solid solutions of Cu in Fe. In addition, the formation of pores at the interface of Mg alloy and steel is adverse for the strength improvement of joints.