Abstract
In this paper, an external magnetic field was introduced to resistance spot welding (RSW) to improve the weldability of A7N01 aluminum alloy. Comparative studies of the macro- and micro-structures, microhardness, and the static and dynamic mechanical properties between welds produced by traditional RSW and magnetically assisted RSW (MA-RSW) were completed. The results show that the external magnetic field could enable larger nugget diameter, the softened columnar grain zone (CGZ-I), the hardened columnar grain zone (CGZ-II) and the finer equiaxed grain zone (EGZ). As a result, compared to traditional RSW joints, the MA-RSW joints exhibited better strength, improved toughness, and greater energy absorption capacity. This resulted in a transition of the failure mode from an interfacial fracture (IF) to a partial thickness fracture (PTF) in lap-shear tests and a BP fracture in cross-tension tests, respectively. In fatigue tests, the larger nugget diameter, hardened CGZ-II and finer EGZ in the MA-RSW welds can inhibit cracks from propagating from EGZ, but from the softened CGZ to the base metal. This change of fracture mode greatly improved the fatigue life of MA-RSW welds under both high and low load conditions.
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