Promoting dissimilar resistance spot weldability of Ti6Al4V alloy to 316L stainless steel by means of employment of Cu55Ni45 alloy interlayer

• Ti6Al4V and 316L were resistance spot welded with Cu55Ni45 interlayer. • Formation of brittle Ti-Fe intermetallics was inhibited with interlayer. • Temperature field was regulated by employing Cu55Ni45 interlayer. • A great enhancement in tensile shear load of joints was achieved with interlayer. • The welded joint with Cu55Ni45 interlayer exhibited hybrid fractured features. Resistance spot welding (RSW) of Ti6Al4V alloy to 316L stainless steel (SS) was carried out with the introduction of Cu55Ni45 alloy interlayer. The weld nuggets with Cu55Ni45 interlayers displayed a significant promotion in the morphology featured by less defect formation than that of the interlayer-free nuggets. Compared with the RSW joints without interlayer, the RSW joint with Cu55Ni45 interlayers with thickness of 200 μm displayed a thinner reactive transition layer with thickness of ∼10 μm in the weld nugget/Ti interfacial zone, and an interfacial reactive transition layer being of serration-like structured features with thickness of ∼2 μm in the weld nugget/SS interfacial zone, respectively. The intermetallics primarily containing FeTi, TiNi 3 , TiNi, Ti 2 Cu and TiCu were formed in the RSW joints with Cu55Ni45 interlayers. The RSW joint with Cu55Ni45 interlayers exhibited a more uniform current field and lower peak temperature during welding process compared with that without interlayers. Moreover, a maximum tensile shear load being 4.3 kN was acquired for the RSW joint with Cu55Ni45 interlayer with thickness of 200 μm, which reaching 87 % greater than that of the RSW joint without interlayers. The RSW joints with Cu55Ni45 interlayers displayed hybrid ductile and brittle fractured features.