A Novel Method Using Electromagnetic Stirring to Improve Resistance Spot Weld Quality of Advanced High Strength Steel (AHSS)

摘要

Electromagnetic stirring (EMS) has been demonstrated to have remarkable effects on the flow and crystallization of molten metal in casting and arc welding processes. In the present study, a novel method based on the use of EMS was proposed aiming on the quality improvement of resistance spot welded (RSW) advanced high strength steels (AHSS). Experimental results on advanced high strength dual phase (DP) steels showed that under the effect of EMS, the weld nugget diameter will be increased, the crystal orientations along the faying surface of workpieces will be less directional, the risk of shrinkage cavities will be lower, and the microstructures in the fusion zone will be refined. As a result, the overall mechanical performance of the welds under EMS effect will be improved in terms of strength, ductility, and fatigue life. Moreover, in order to understand the fluid flow driven by magnetic force and the temperature-dependent physical properties in RSW process, a multi-physics model, which comprehensively considers the coupling of electric, magnetic, thermal and flow fields, was proposed. Results showed the strong flow of the molten metal driven by the induced magnetic force will dramatically affect the heat transfer and reduce the temperature gradient in the weld nugget. It could be expected that after in-depth studies in the future, the EMS-bascd quality control method will have great potential in the application of RSW for AHSS, ultra-HSS, and even aluminum alloys.