Influence of Different Process Parameters on Microstructural and Mechanical Properties of Cold Metal Transfer Joining of DP 600 Steel and Al 5052 Alloy

In this paper, cold metal transfer (CMT) welding-brazing of automotive grade dual phase steel with Al 5052 alloy using ER 4043 filler wire was studied. The present work objective is to discuss about the influence of different process parameters such as wire feed rate (WFR) and generated heat input on joint quality and microstructure of the dissimilar metal and to predict the current-voltage characteristics to analyse process stability of the process. The Cyclogram and current-voltage transient graphs exhibit the stability of the CMT process, suitable for joining dissimilar metals like Al and steel. The mechanical and microstructural properties of an overlap joint were examined by using shear-tensile test, microhardness test and metallographic technique. At WFR 5 m/min and torch position 0.6 mm, the highest failure load of 4.0 kN was achieved due to the better wettability of molten filler on base metal and increased interfacial area of deposited bead. The microstructure shows the variation in the intermetallic (IM) layer at different WFR and the zinc accumulation at the toe of the bead. The microstructural morphology and EDS analysis show the presence of hard and brittle Al-Fe-Si ternary phases and IM layer at the brazing interface of the joint. In addition, spillage, and clusters of needle-shaped IM phases into the bead were also seen due to the high turbulence in the weld pool when WFR increased. Variation in IM layer thickness and zinc accumulation was also observed in microstructural analysis of the bead and joint. Failure load increased initially while raising the WFR but then decreased at torch position of − 0.6 mm at WFR 5 m/min despite an increase in wettability, it was due to the presence of hard and brittle IMCs and cracks developed in the IMC layer due to the residual stress and solidification shrinkage.