Physically-based constitutive models for hot gas pressure forming of laser-welded titanium alloy blank

Weld seam (WS) has a different microstructure with base metal (BM), which could result in nonuniform deformation of the welded titanium alloy blank during hot forming process. In this paper, physically-based constitutive models considering microstructure evolution during the hot deformation were developed for both WS and BM to improve prediction accuracy of simulation. Uniaxial tensile tests of WS and BM were carried out to get stress-strain curves at temperatures ranging from 850 to 950 °C and strain rates ranging from 0.001 to 0.1 s⁻¹. Microstructure evolutions of both WS and BM were characterized to reveal the deformation mechanisms. The developed models were validated by both strain rate jumping tensile tests and hot gas pressure forming of the welded blank. Results show that the physically-based constitutive models have good predictions of flow stress, globularization of WS and dynamic recrystallization of BM. The effect of WS on nonuniform deformation during the hot gas pressure forming of a laser-welded TA15 titanium alloy blank was accurately simulated. Physically-based constitutive models could reflect the effects of loading history on the microstructure evolution and flow stress. Therefore, compared with the simulation using the phenomenological constitutive models, the prediction accuracy of thickness distribution could be improved from 73.7 % to 90.8 % by the application of physically-based constitutive models.