Dissimilar metal joining of Q235 mild steel to Ti6Al4V via resistance spot welding with Ni–Cu interlayer

Abstract

Dissimilar metal joining between Q235 mild steel and TC4 titanium alloy was carried out via resistance spot welding with Ni–Cu alloy as filler metal (abbreviated as resistance welding with interlayer). The results were compared with the welded joints obtained by directly conventional resistance spot welding without interlayer (abbreviated as D-RSW). The effect of Ni–Cu alloy on the macro-characteristics, interfacial structure, and microstructure, mechanical properties (including shearing force and microhardness) of the welded joints were investigated. Also, the temperature field in the actual welding process was dynamically simulated using MSC.Marc software, which validity of the numerical results was confirmed by the actual temperature collected at the same location via the infrared thermal imaging. The results showed that the maximum temperature was less than the melting point of TC4, Q235, and interlayer. The reaction layer and diffusion layer were formed between TC4 and Q235 by atomic diffusion due to the introduction of the interlayer, which replaced the welding nugget generated in the D-RSW welding process. Ti2Ni, Cu3Ti2, TiNi, TiCu, and TiFe2 intermetallic compounds (IMCs) could be generated at the welded joints by resistance welding with interlayer. Moreover, there were no other welding defects in the welded joints. The maximum ultimate shearing force was up to 12,726 N in this way, which was more than twice that obtained by D-RSW. Correspondingly, the interfacial fracture was obtained for the former instead of the brittle facture for the latter. There was a narrow range of highest-value microhardness according to the reaction layer.