Novel postweld heat treatment method for improving mechanical properties of resistance spot weld

A novel postweld heat treatment method by applying cross-direction welding current (cross-current) was applied on the resistance spot weld. The effect of cross-current on the nugget shape, microstructure and mechanical properties was investigated. The results show that the cross-current postweld heat treatment enhances the efficiency of postweld heat treatment and improves the mechanical performance of nugget. The cross-current promotes the recrystallisation of nugget microstructure, which induced the transformation of microstructure from column crystal to quasi equiaxed grain. The quasiequiaxed grains of martensite in the weld nugget significantly increase the microhardness of weld nugget and the tensile shear force of weld joint.