Microstructure and properties of steel/magnesium joint for adhesive layer-Ni foil assisted laser welding

DP590 dual-phase steel with thickness of 1.4 mm and AZ31B magnesium alloy with thickness of 1.5 mm were welded by adhesive layer-Ni foil assisted laser welding technology in an overlap steel-on-Mg configuration. Foil elements were selected based on thermodynamic calculation, weld morphology, microstructure and mechanical properties of the joint were analyzed, and the temperature field and flow field of molten pool were simulated. The results show that under the conditions of laser power of 1 800 W, welding speed of 30 mm/s, defocusing amount of + 2 mm and flow rate of 15 L/min, the metallurgical connection between magnesium and steel can be realized by adding Ni foil. While adding adhesive layer and Ni foil, the average shear strength of the joint is increased by 1.73 times compared with that of single Ni foil. The weld is continuous and smooth with the addition of adhesive layer, the melt width of magnesium side molten pool increases, the transverse bonding area of steel/magnesium increases, the transverse and longitudinal temperature gradient at interface decreases, the flow velocity of molten pool increases, and the element distribution uniformity is improved, which promotes the diffusion and metallurgical reaction of interfacial elements. Hence, the performance of the steel/magnesium joint is improved greatly.