Quality improvement in resistance spot weld of advanced high strength steel using external magnetic field

Electromagnetic stirring method has been used in casting and arc welding processes to refine crystal grains. In this paper, the authors describe an experiment where an external magnetic field (EMF) produced by a pair of permanent magnets was used to study the effect of electromagnetic stirring on resistance spot welding of advanced high strength steel DP780. Experimental results show that under the same welding current, the EMF could refine the crystal grains, increase the weld nugget diameter, reduce the risk of shrinkage cavities and significantly improve the joint's tensile–shear strength and ductility. However, when the welds with and without the EMF were compared under the same weld diameter, because of the greatly reduced nugget thickness, the tensile–shear strength of the weld made under the EMF is a little bit lower than the normal weld.