Workpiece property effects on nugget microstructure determined by heat transfer and solidification rate during resistance spot welding

Abstract

This study theoretically investigates workpiece property effects on nugget microstructure determined by temperature gradient and solidification rate during resistance spot welding. Dimensionless properties include Curie temperature, thermal conductivity and specific heat ratios between solid and liquid, equilibrium partition coefficient, and electrical and thermal conductivity ratios between electrode and workpiece. Based on a previous realistic transport model, the computed results show that a lower morphology parameter due to smaller heat flux and higher solidification rate in radial direction near the faying surface than that in axial direction near the axisymmetric axis is responsible for equiaxed grains usually observed in the central region. Morphological parameters decrease as the liquid-to-solid specific heat ratio and equilibrium partition coefficient increase, and Curie temperature decreases. Cooling rates responsible for the primary and secondary dendrite arm spacings, however, are uncertain. Other property parameters exhibit definite and uncertain effects on cooling rate and morphology parameter, respectively. The effects of workpiece properties on weld microstructures are revealed.