Particle simulation of nugget formation process during steel/aluminum alloy dissimilar resistance spot welding and thickness estimation of intermetallic compounds

Abstract

A steel/aluminum alloy dissimilar resistance spot welding process was simulated by a three-dimensional smoothed particle hydrodynamics method. Furthermore, the time dependent increase of the intermetallic compound thickness on the joining interface was estimated using the numerical data of the temperature history obtained by the simulation. As a result, the steel sheet started to melt from the center of the sheet in the thickness direction and formed a nugget, while the aluminum alloy sheet started to melt from the joining interface and formed a nugget. The convection in the molten aluminum alloy caused by the electromagnetic force promoted the heat transfer at the solid-liquid interface because the temperature gradient become steeper due to the conduction, whereas the temperature near the nugget center decreased. Moreover, the numerical estimation indicated that the intermetallic compound layer was thicker near the center of the joining interface and thinner toward its edge. The maximum thickness was estimated to be approximately 1 μm, which was the same order of magnitude as the experimentally obtained value. These results support the validity of the computational model developed in this study for simulating the nugget formation process during dissimilar resistance spot welding and estimating the intermetallic compound thickness.