Microstructure and mechanical properties of TC4 titanium alloy and 316L stainless steel joint by MIG welding with mortise structure

This work designed a new mortise structure on the to-be-welded side of TC4 titanium alloy sheet and successfully obtained MIG-welded joint of TC4 titanium alloy (TC4) to 316 L stainless steel (316 L) with high strength and toughness through the synergy of mortise structure and metallurgical bonding. The effect of mortise structure on the interfacial microstructure, mechanical properties and fracture behaviour of dissimilar joints was investigated. Various intermetallic compounds, like Ti2Cu, Ti2Cu + TiCu, and AlCu2Ti phases, formed in Ti/Cu reaction interface. The Ti/Cu interfacial layer perpendicular to the horizontal direction was generated in the mortise structure on Ti side, and the Ti-Cu phases in the inner layer of mortise sidewall evolved from coarse columnar to spherical morphology. The results showed that the mortise structure significantly improved the strength of joints. The joint with mortise structure had a maximum tensile strength of 549 MPa, which was 93.8% of the strength of the stainless steel substrate. Simultaneously, the joint with mortise structure deformed significantly before failure, and the fracture surface revealed numerous dimples on the 316 L side.