Characteristics of Torch-Offset Cold Metal Transition-Cycle Step Welding of 5052Al Alloy with T2 Copper via Al-12Si Filler

CMT cycle-step (CMT-CS) is a novel mode in CMT welding. It has the characteristics of minimal heat input, droplet size control and a high degree of automation. This work proposed a torch-offset CMT-CS welding method to join 5052 Al alloy to T2 copper with Al-12Si filler in different joint configurations. The influence of joint configuration was investigated, in terms of weld heat input, weld appearance, weld defect, interfacial microstructure, joint mechanical properties and fracture mode. The results indicated that offset distance to copper increased the weld heat input and promoted the wettability of Al-Si liquid filler wire on the substrate. The change of offset distance and joint configuration will change the melting amount and heat transfer form of copper, thus changing the composition of the reaction layer. The average joint strength of the Al/Cu (Aluminum alloy on top) joint was slightly higher than that of the Cu/Al (pure copper on top) joint. The maximum values were 129 N/mm and 127 N/mm, respectively. As the offset increases, the joint failure shifts from the fusion zone to the interface; moreover, the fracture mode was changed from brittle fracture to ductile fracture.