Effect of external magnetic field on resistance spot welding of aluminium to steel

Resistance spot welding of aluminium to steel with magnetic-assisted apparatus was performed for the first time to understand the metallurgical joining mechanism in the melt region and at the material interface. The electromagnetic force promoted circular motion of the molten metal and accelerated the diffusion of Fe atoms to the aluminium sheet, which induced finer grains, thinner intermetallic compound layers, reduced interface defects, and elevated hardness of the resulting aluminium nugget. Coach peel tests revealed that welds made with an external magnetic field presented enhanced strength and ductility compared to welds made with no external magnetic field. The enhanced strength and ductility resulted in a transition of the fracture behaviour from brittle interfacial mode to ductile button pullout mode, and increased the peak load and the energy absorption by 90% and 1327%, respectively.