Enhanced strength of laser welded steel/titanium butt joints with vanadium multi-layers and a copper plate as a composite intermediate layer

• A novel composite interlayer prepared with V multi-layers and a CrZrCu plate is introduced to join steel/Ti joint. • A sound steel/Ti joint is successfully obtained using the prepared composite interlayer. • The steel/Ti joint with 1.2 mm-thick V layer possesses the maximum UTS of 418 MPa and an EI of 15 %. • It can be found that Cu solid solution and V solid solution are generated in the FZ and FZ/V interface at TC4 alloy side. Vanadium (V) interlayers of 0.4 mm, 0.8 mm, and 1.2 mm thickness were firstly deposited on the TC4 alloy side using a laser metal deposition (LMD) process, which was then combined with a CuCrZr plate as a composite intermediate layer, for dissimilar laser welding of TC4 titanium alloys to 304 stainless steels (SS) successfully. The effects of different thicknesses of V interlayers on the weld shape, microstructure and mechanical properties of TC4/304SS joints were investigated. The results show that a sound TC4/304SS butt joint with full penetration is successfully obtained using the prepared composite interlayer. The TC4/304SS joint exhibits a maximum ultimate tensile strength (UTS) of 418 MPa and an elongation index (EI) of 15 % with a V layer thickness of 1.2 mm. With the V-layer thickness increasing, the size and content of the V-Cu solid solution in the fusion zone (FZ) on the TC4 alloy side are gradually increased without the formation of intermetallic compounds (IMCs) generated.