Interfacial Characteristics of Ti/Steel Joints Welded by Resistance Spot Welding with Bi-Interlayer of Nb-Ni

Resistance spot welding was performed to join 2 mm thick TA2 titanium plate and Q235 steel plate using an Nb-Ni bi-interlayer. The microstructure of the interfacial zone was observed and analyzed, and the tensile shear load of the joint was evaluated. The joints obtained display double-nugget-type and penetration-type joints. For the double-nugget-type joint, Ni6Nb7 and Ni3Nb layers have been formed in the region between the residual Nb layer and the steel, while for the penetration-type joint, a mixed nugget composed of Ti-Fe intermetallic compounds was formed at the center zone of the weld. As the welding current increased or welding time extended, the tensile shear load of the joint exhibited a trend of initially increasing and subsequently decreasing. When a bi-interlayer consisting of 0.05 mm-Nb and 0.04 mm-Ni is utilized, the tensile shear load of the joint reached the maximum value of approximately 8.7 kN under the condition of 11 kA welding current, 300 ms welding time, and 3 kN electrode pressure. The results indicate that the Nb layer can effectively impede the cross-interface diffusion of Ti atoms and Ni-Nb intermetallic compound layers are formed in the interface region in the case that the interlayer thickness and the welding parameters are well-matched when resistance spot welding of Ti/steel is performed with a bi-interlayer of Nb-Ni.