Investigation on microstructure and mechanical properties of Al/Cu butt joints by CMT method in asymmetrical V-groove configuration

It is a challenge work for joining of Al to Cu by conventional fusion welding method. This study investigates butt joining of 6061 Al alloy to pure copper using cold metal transfer (CMT) process in asymmetrical V-groove configuration. The microstructure and mechanical properties of Al/Cu butt joints are revealed. The microstructure in the fusion zone mainly consists of alpha (Al) and Al2Cu phase accompanied with Si phase. The two-layer intermetallic compound (IMC) layers are exhibited at the Al/Cu interface. The first IMC layer near the copper is a thin layer in thickness of less than 5 mu m. The second IMC layer is in the irregular non-linear and zigzag shape with some particles dispersed at the boundaries. XRD analysis shows that the IMCs in the joints mainly contain Al2Cu, AlCu, Al3Cu4 and Al4Cu9 phase. The ultimate tensile strength (UTS) of the joints could reach 108 MPa. The fracture paths of the joints are along the Al/Cu interface. The pores and IMCs are main factors to determine the strength of the joints. Since the pores are at the Al/Cu interface, the UTS of the joint is lowered at low wire feed rate. The joints break along the Al/Cu interface due to the brittle IMC layer at high wire feed rate. It can be achieved Al/Cu butt joints with sufficient strength in asymmetrical V-groove configuration.