Microstructure and Properties of Laser Welding-brazing Joint of Magnesium Alloy and Copper, Nickel Plated Steels

The laser brazing of magnesium alloy/Ni（Cu） plated steel was carried out by using AZ31 magnesium alloy welding wire, and the effects of Cu layer and Ni layer on the microstructure and properties of laser welding brazed joints were discussed. The results indicate that whether the Cu layer or the Ni layer is plated on the surface of Q235 steel, the macroscopic morphology of the laser welded joint is good. The tensile strength of the welded joint obtained by plating Cu layer on the Q235 steel plate is 145.4 MPa, reaching 60.6% of the strength of the magnesium alloy. Compared with the welded joint obtained by plating Ni layer on Q235 steel, it is increased by 20.8%. Through scanning electron microscopy, it is observed that the flocculent structure is formed at the interface of Cu-plated steel, while the granular structure is formed at the interface of Ni-plated steel. Through SEM and XRD analysis, the fracture at the side of magnesium in the joint of copper plated steel plate mainly has CuMg₂, Cu₃Al₂ and Al₅Mg₁₁Zn₄ phases, and the fracture at the side of magnesium in the joint of nickel plated steel plate mainly has MgNi₂, Al₃Ni₂ and Al_0.58Mg_0.42 phases.