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 crosssections 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.Titanium alloys are found extensive applications including aerospace, marine, chemical, and medical industries due to their excellent properties such as good high temperature performance, high specific strength, good creep resistance, biocompatibility, and good corrosion resistance [1]. Ti-alloy complex tubular components are widely used in petrochemical equipment, vehicle exhaust system, sports equipment and piping system of ship, air-inlet system, and hydraulic control system of aerospace and aviation [2, 3]. However, for titanium alloy, it is hard to be formed at room temperature because of high springback and low plasticity. The problems can be counteracted by improving the forming temperature. In recent years, superplastic forming (SPF) were popularly used to form complex components at elevated temperature [1,4,5]. Nevertheless, the disadvantages of localized thinning, expensive microstructure refining processing, low productive efficiency, and high deforming temperature in superplastic forming limit applications of Ti-alloy SPF. Thus, it is urgent need to develop a forming technology with low energy consumption, high efficiency, and without microstructure refining processing.Quick plastic forming, developed by General Motors to form AA5083 aluminum automobile body panels, affords comparable capabilities yet at higher production rates due to lower forming temperature, higher strain rates, and without refining grains [5,6]. R. Neugebauer [7], A.W. Dykstr [8], W. Xin [9], and B. Dykstra [10] set up hot metal gas forming (HMGF), and mainly investigated and applied the process on forming of aluminum and magnesium alloy components. J. Liu [11,12], utilizing the mechanical pre-forming, investigated the AA5083 sheet gas forming using argon gas at 400°C. W.J. Kim [13] formed an Al-Mg-Cr aluminum suspension component successfully at 520°C under a constant gas pressure of 7 MPa d...

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