High-cycle fatigue behavior of MIG brazed galvanized DP600 steel sheet joint—effect of process parameters

Abstract

Metal inert gas (MIG) brazing is a potential process for joining coated automotive steel sheets over conventional fusion welding process. 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, microhardness, nano-hardness, shear tensile strength, and high-cycle fatigue behavior of MIG brazed lap joint of 1.4-mm-thick zinc-coated (galvanized) DP600 steel sheet using Cu-Al filler wire. It has been possible to obtain 98 % joint efficiency using Cu-Al filler wire 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) in-between fusion zone and steel substrate has been characterized by X-ray and nano-hardness testing which confirmed the presence FeAl intermetallic compound. 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.