Interfacial layer regulation and its effect on mechanical properties of Ti6Al4V titanium alloy and T2 copper dissimilar joints by cold metal transfer welding

TC4 titanium alloy and T2 copper sheets were joined by cold metal transfer welding with ERCuMnNiAl filler metal, and the influence of interfacial microstructure on the mechanical properties and fracture behavior of resultant joints was investigated. β-Ti phase and various intermetallic compounds, such as Ti2Cu, TiCu, and AlCu2Ti phases, were orderly formed in Ti/Cu reaction zone. The AlCu2Ti phase has blocky and island-like morphology, and increasing welding heat input accelerated the transformation of AlCu2Ti phase from blocky to island-like, resulting in a significant change in the properties of joints. All the joints fractured along the interface on Ti side due to the inferior performance of AlCu2Ti phase. The fracture behavior was strongly related to the thickness and distribution of AlCu2Ti phases. And the joints with different welding heat input of 2.06 kJ/cm, 3.40 kJ/cm, and 4.28 kJ/cm exhibited cleavage, ductile-brittle-mixing, and quasi-cleavage fracture, respectively. The suitable thickness (10.22 μm) of blocky AlCu2Ti and the dispersive distribution of island-like AlCu2Ti were formed when the welding heat input was 3.40 kJ/cm, and the average tensile strength of the joint reached 186 MPa.