Numerical analysis of the effect of heat loss by zinc evaporation on aluminum alloy to hot-dip galvanized steel joints by electrode negative polarity ratio varied AC pulse gas metal arc welding

Abstract In joining of aluminum alloy to hot-dip galvanized (GI) steel by arc welding-brazing process, evaporation of zinc (Zn) layer and formation of brittle Fe Al intermetallic compound (IMC) layer can affect the joint quality both thermally and metallurgically. At this point, the alternate current pulse gas metal arc welding (AC pulse GMAW) process is an excellent joining method because of its relatively low heat input to the base metal by controlling the electrode negative polarity (EN) ratio in its current waveform. In this study, a numerical analysis of joining 1.2 mm-thick GI steel to 1.2 mm-thick AA5052 aluminum alloy in the lap configuration using AC pulse GMAW was conducted to determine the effect of the EN ratio and Zn evaporation on joint quality. Based on the finite element method (FEM) 3D heat transfer model, the heat conduction analysis and the estimation of the IMC layer growth at the joint interface were carried out. The calculated results were validated with the corresponding experimental results and demonstrated a fair agreement. The results indicated that the temperature-dependent Zn mass evaporation and the increased EN ratio decrease the heat input to the joint interface. In particular, the heat loss caused by Zn evaporation with its latent heat restricts the growth of the brittle Fe Al IMC layer, which follows a function of temperature variation per unit length and time, by decreasing the heat from the arc to the joint interface. A 7.83 μm-thick IMC layer was obtained at a welding current of 55 A with an EN ratio of 20%, and a sound dissimilar material joint was achieved.