Correlation between softening mechanisms and deformation non-uniformity of laser-welded titanium alloy tube during gas bulging process

In this paper, post-weld annealing was carried out to adjust the flow stress difference between weld seam and base material (BM). Deformation non-uniformity of laser-welded titanium alloy tubes before and after annealing was evaluated by gas bulging at 800 °C. Results show that after double annealing (950 °C/2 h, air cooling + 600 °C / 2 h, air cooling), weld seam and BM had similar peak stress at first during tensile test at 800 °C, 0.001 s− 1, then the flow stress difference between them changed dynamically due to different softening rates. The maximum flow stress difference ratio was reduced from 36% to 17% after annealing. Deformation uniformity of the bulged tube was improved by 24.6% after annealing, but the higher softening rate of BM during gas bulging confined its further improvement. At early stage of gas bulging of the annealed tube, the main softening mechanism for weld seam was dynamic recovery and that for BM was globularization of secondary α and phase transformation of α to β. At middle-late stage of gas bulging, the main softening mechanism for weld seam was partial globularization of lamella α and that for BM was wide dynamic recrystallization.