热循环对 TC4 钛合金窄间隙焊接接头组织和性能的影响

Thermal cycling has a significant impact on the microstructure and properties of narrow-gap welded joints in titanium alloy thick plates. In this study, a 60 mm-thick TC4 titanium alloy welded joint was fabricated using oscillating-wire magnetic-controlled arc narrow-gap welding technique. The evolution of the microstructure (α phase, β phase, and grain boundary α_GB), as well as changes in microhardness and its tensile properties under typical thermal cycling conditions were investigated through numerical simulation. The results show that high-temperature thermal cycling induces a complete α→β transformation, promoting the preferential growth of the α phase and forming coarse and uniformly-oriented α colonies. In contrast, subsequent low-temperature thermal cycling causes an incomplete α→β transformation, where lower cooling rate and temperature gradient weaken the preferential orientation, leading to the refinement of lamellar α phase. After the entire thermal cycling process, the thickness of lamellar α phase increases from 0.91±0.09 μm to 1.02±0.18 μm, and the proportion of residual β phase increases from 0.02% to 1.89%. The weld root layer exhibits the highest microhardness, attributed to grain refinement strengthening. The root layer also demonstrates the highest tensile strength, while the cap layer shows the highest elongation. The joints exhibit ductile fracture behavior overall.