Effects of Post-Annealing Heat Treatment on the Microstructure and Performance of TC4 Titanium Alloy in Curved Path Laser Wire Filling Welding

This study investigates the effect of post-annealing heat treatment on the microstructure and properties of welded joints in TC4 titanium alloy after curved path laser wire filling welding. The results reveal that in the untreated joint, the base metal exhibits an α + β lamellar structure, the weld zone contains α′ acicular martensite, and the heat-affected zone (HAZ) shows a mixed α and α′ structure. Post-annealing leads to coarsening of the α′ martensite structure, with increasing temperature and duration resulting in grain growth. Microhardness decreases from the weld zone to the HAZ and base metal. After heat treatment, the weld zone’s microhardness increases by 12.2 HV and the HAZ by 10.8 HV. Tensile fracture in untreated joints occurs in the base metal, with joint strength exceeding that of the base material. At 650°C for 2 h, the tensile strength of the heat-treated joint improves compared to the untreated state, with ductile fracture observed. However, extending the holding time to 3 h results in coarser grains and reduced tensile strength.