Effect of thickness of transition layer on the microstructure and properties of the titanium/stainless steel welds with oscillating laser

Titanium (Ti)/stainless steel weld joints with copper (Cu) transition layer thicknesses of 0.2, 0.4, and 0.6 mm were studied through combined experimental and finite element methods. Then, the formation mechanism and distribution of the Ti–Cu compounds (intermetallic compounds, IMCs) were analyzed. The results showed that the thicknesses of the Ti–Cu IMCs decreased with increasing thickness of the Cu layer, and the tensile strength and elongation increased when welding was conducted under a ring oscillation laser with a spot diameter of 0.3 mm, an oscillating diameter of 0.1 mm, a welding speed of 220 cm/min, and a laser power of 2000 W. In the 0.2 and 0.4 mm Cu layers, Ti–Fe IMCs appeared in the welds, and the thicknesses of the Cu–Ti IMC layers were 60 and 30 μm, respectively. When the 0.6 mm Cu transition layer was used, a pure Cu layer appeared in the weld, which effectively inhibited the formation of Ti–Fe IMCs. The thickness of the Cu–Ti IMC layer was reduced owing to the faster cooling rate at the Cu–Ti interface. Furthermore, the Cu4Ti phase was distributed in a thin area of 15 μm, which improved the mechanical properties of the welded joint and allowed the tensile strength to reach 330 MPa. Compared to the welding joints with Cu layer thickness less than or equal to laser irradiation width, the joints with Cu layer thickness larger than laser irradiation width have a significantly improved tensile strength.