Microstructure and mechanical property improvement of dissimilar metal joints for TC4 Ti alloy to 301L stainless steel

Pulsed laser welding of Ti alloy to stainless steel (SS) has been applied using pure V as an interlayer. Microstructures and mechanical properties of joints were improved by changing laser offset. Two-pass welding was applied, and two weld zones were produced in the joint. The unmelted V interlayer acted as a barrier to mixing of the two base materials during welding. The melting amount of base materials and V interlayer was controlled by changing laser offset to control the fusion ratio and thus to improve joint microstructure. σ-Phase was present in V–SS weld zone of joint with laser offset of zero, which resulted in failure of the joint. Through changing laser offset, V concentration in V–SS weld zone of SS-0.2 mm offset joint was decreased and σ-phase was eliminated in the joint. ω-Phase was discovered in Ti alloy–V weld zone of zero-offset joint, which had an adverse effect on mechanical property of the joint. Through changing laser offset, V concentration in Ti alloy–V weld zone of V-0.2 mm offset joint was increased and precipitation of ω-phase was prevented. Three joints (zero-offset joint, SS-0.2 mm offset joint and V-0.2 mm offset joint) exhibited the tensile strength of 504, 548 and 599 MPa, respectively.