Effects of Si element on the weld formation and microstructure of titanium/steel dissimilar joints

Welding of 1mm thick TC4 titanium alloy and 304 stainless steel was performed using T2Cu and CuSi3 welding wires under the same process parameters. The metallurgical behavior of the TC4/304 dissimilar metal weld pool was studied using optical microscopy(OM) and scanning electron microscopy(SEM). A comparative analysis was conducted on the effects of different wire compositions, particularly the addition of silicon (Si), on the macro formation of the TC4/304 dissimilar metal joints, the microstructure at the interface, and the mechanical properties. The results showed that the addition of Si significantly enhanced the fluidity of the liquid weld pool, eliminated defects such as depressions and pores, and addressed issues of poor fusion at the back of the weld, leading to substantial improvements in macro formation of the welds. Both types of welding wires effectively hindered the diffusion of Ti and Fe atoms, preventing the formation of Ti-Fe compounds at the Ti/Cu interface, although a small amount of Ti-Fe phase was present at the center of the weld and at the Cu/Fe interface. The sufficient Si content in CuSi3 welding wire not only promoted more effective nucleation and growth of the Ti₅Si₃ phase but also allowed for its uniform distribution throughout the weld due to the flow of the weld pool, providing a dispersion strengthening effect for the joint. Compared to T2Cu welding wire, the joints obtained with CuSi3 welding wire exhibited a tensile strength increase of 81.4%, reaching a maximum of 366.8 MPa.