Shear Tensile and High Cycle Fatigue Performance of MIG Brazed DP600-GI Steel Sheet Joint

MIG brazing is a potential process for joining coated automotive steel sheets over conventional fusion welding process such as gas metal arc welding (GMAW). However, understanding the process variables on the joint performance is not yet clear. This paper deals with details study on the effect of process parameters and two different modes of operation (push and pull) on bead geometry, microstructure, shear tensile strength and high cycle fatigue behavior of MIG brazed lap joint of 1.4 mm thick galvanized DP600 steel sheet using solid CuAl8 filler wire. It has been possible to obtain 98% joint efficiency due to dispersion hardening effect of fusion zone consisting of dispersed iron from base metal in copper matrix. Also, an interface region formed (~6 μm) inbetween fusion zone and steel substrate has been characterized. High cycle fatigue test of all MIG brazed joints showed fatigue endurance (2 million cycles) at 10% of tensile load and fatigue life increased with increasing heat input. Interestingly, three different fatigue failure paths were observed with different loading cycle, such as interfacial failure; fusion zone failure and fine grain heat affected zone failure where the bead geometry played an important role in brazed joint under dynamic loading condition.