Improve resistance spot weld quality of advanced high strength steels using bilateral external magnetic field

Abstract Magnetically assisted resistance spot welding (MA-RSW) process has been verified capable of improving weld quality of advanced high strength steels. In the original MA-RSW process, a pair of axial mutually repulsive circular permanent magnets was adopted to produce a radial magnetic field in weld nugget region. However, the circular magnets lead to interference problems with surrounding work-pieces or fixtures in welding process, which restricts its wide use. To solve this problem, in this paper, a bilateral magnetically assisted apparatus was developed, which used a pair of axial mutually repulsive magnets with a volume of nearly 60 % smaller than that of the conventional circular one and thus could significantly avoid interference in production environment. To investigate the improvement effect of the small-sized magnetic assisted apparatus, two types of MA-RSW process, e.g. bilateral MA-RSW (BMA-RSW) process and circular MA-RSW (CMA-RSW) process were investigated on 1.6 mm thick bare dual-phase steel DP590 through comparing with the traditional RSW process. The results showed that although the stirring region in BMA-RSW process is much smaller due to its small volume, it could achieve almost the same improvement effect as the CMA-RSW process in terms of weld lobe, macro morphology, microstructure and mechanical properties, due to its stronger local stirring effect underneath the bilateral permanent magnets.