Study on the mixed dynamic recrystallization mechanism during the globularization process of laser-welded TA15 Ti-alloy joint under hot tensile deformation

In this article, the hot deformation mechanism of a laser-welded near α TA15 Ti-alloy joint was studied by hot tensile tests conducted at temperatures ranging from 800 °C to 900 °C with strain rates ranging from 1.0 × 10− 1 s− 1 to 1.0 × 10− 3 s− 1. The results show that the main hot deformation mechanism of the laser-welded TA15 Ti-alloy joint is continuous globularization, but dynamic recrystallization (DRX) plays an important role during the globularization process. The morphology of α phase exerts considerable influence on the DRX mechanism. When the lamella microstructure is dominant in the weld seam, continuous dynamic recrystallization (CDRX) is the active mechanism; whereas with the increasing fraction of equiaxed grains in the weld seam, discontinuous dynamic recrystallization (DDRX) seems to be the dominant mechanism during the tensile deformation. The globularization process can be divided into three stages based on the characteristics of the microstructure. Under such a deformation mechanism, the laser-welded TA15 Ti-alloy joint tends to have a good formability at high temperature and small strain rate. A maximum elongation of 292% was achieved at 900 °C, 0.001 s− 1, which exhibits superplastic characteristics.