Optimization of magnetic oscillation system and microstructural characteristics in arc welding of Al/Mg alloys

AZ31B magnesium alloy and 6061 aluminum alloy were welded by the longitudinal magnetic field hybrid cold metal transfer (CMT) welding process. Three magnetic pole structures were designed and the distributions of magnetic field were simulated. The results show that the platform-shaped magnetic pole structure can improve the longitudinal direction of magnetic field in weld zone, which was suitable to redistribute welding heat source and decrease welding spatters. With the applied magnetic oscillation the welding width increased, the welding penetration and wetting angle decreased, meaning the wetting behavior of molten metal improved. The welding pores in the weld zone were suppressed with the increase of coil currents. The magnetic oscillation obviously reduced the thickness of Mg ₂ Al ₃ layer and dispersed the distribution of strengthening phases Mg ₂ Si that can prevent the crack propagation. The microhardness value at the interface layer was increased and the shear strength of the Al/Mg joints reached a maximum of 1411 N with magnetic oscillation, increasing by 30% compared to the normal welded joint. Fracture of the Al/Mg lap joints occurred at the Mg ₂ Al ₃ layer/weld interface and Al side around the fusion line.