Loading path and microstructure study of Ti-3Al-2.5V tubular components within hot gas forming at 800 °C

Abstract

Hot tube gas forming is a forming technology, whose ultimate goal is forming a uniform cross-section blank tube into a complex shape die cavity with varying cross-sections without necking, wrinkling, or buckling by applying of axial feeding and internal pressure at elevated temperature. In this paper, the effects of feeding speed and internal pressure on the quality of formed tubular components were studied by theoretical analysis, FEM simulation, and experiment. The microstructure evolutions at four typical positions were analyzed by electron back-scattered diffraction (EBSD). The mechanical properties of tubular component were tested by the uniaxial tensions and hardness tests. A good tubular component can be formed under a two-stage loading path at 800 °C, the feeding speed is 0.1 mm/s and the internal pressure is 5 MPa during the first feeding stage while the feeding speed is 0.2 mm/s and the internal pressure is 7 MPa during the second feeding stage. At the forming zone, the grains are significantly elongated along the hoop direction. Compared with the as-received tube, the tensile strength of parts reduces about 6 % along axial direction.