CMT welding-brazing of al/steel dissimilar materials using cycle-step mode

Cycle step (CS) process is an advanced mode in cold metal transfer (CMT) welding technology, in which allows to set both the numbers of individual droplets and the pause time between cycles. This novel mode enables a reduced weld heat input and exhibits clear-rippled beads with high degree of reproducibility and high tolerance for workpiece gaps. In the present study, the CMT-CS process was used for welding-brazing of AA5052 aluminum alloy to galvanized low carbon steel with Al-5Si filler wire. A visually acceptable weld with clear fish-scale ripples was successfully obtained in a lap joint configuration. The influence of CMT cycle and interval time on the weld heat input, weld morphology, microstructure and mechanical properties of aluminum/steel dissimilar joints was explored. The results showed that the increase of CMT cycles led to the increase of weld heat input and it in turn increased the braze width and deceased the contact angle; while, the increase of interval time resulted in the decrease of weld heat input and it increased the weld spot spacing and decreased the density of the fish-scale ripples. The change of CMT cycle and interval time had very limited impact on the phase composition of the interfacial reaction layer. The joint strength basically increased with the increased CMT cycle; while, it increased first then deceased with the increased interval time. Two kinds of fracture modes were observed, namely interfacial shear failure and fusion zone failure. The bending angle decreased with the increase of weld heat input.