Effect of external magnetic field on resistance spot welding of aluminum alloy AA6061-T6

An external magnetic field is applied in resistance spot welding (RSW) of 3 mm thick AA 6061-T6 sheets to improve the weld quality. Under the action of the external magnetic field, an additional circumferential flow is generated, resulting in the reduction of cooling rate and the change of solidification mode, and it finally influences the nugget profiles, microstructural evolutions, and mechanical properties. The profile of the magnetically assisted resistance spot welding (MA-RSW) nugget became more regular and freer of defects, e.g., the internal shrinkage defects and eyelash-like hot cracks. Moreover, a double-layered columnar grain zone and a nearly single-structured equiaxed grain zone were finally obtained. The tensile properties of the MA-RSW welds were significantly improved by increasing nugget diameter, eliminating defects, and complicating the crack propagation path. As a result, the application of the external magnetic field could achieve an energy-saving effect.