Formability and microstructure of TC4 titanium alloy hollow shafts formed by cross-wedge rolling with a mandrel

The formability and microstructure of TC4 titanium alloy hollow shafts formed by cross-wedge rolling (CWR) are being investigated to ensure that products manufactured for utilisation in the aviation sector are lightweight. The flow behaviour of the TC4 alloy was studied via isothermal hot compression tests. The constitutive equations in different phase regions were then established and applied to a finite element (FE) model to study the effect of process parameters on the ellipticity of the TC4 alloy hollow shafts formed by CWR. Corresponding CWR experiments were conducted to validate the FE model; further, the microstructure of the TC4 alloy hollow shafts was investigated. The results demonstrate that forming angle, stretching angle and area reduction considerably affect the ellipticity of the TC4 alloy hollow shafts by varying the contact area between a die and a workpiece. The ellipticity evidently increases as the relative wall thickness decreases, as the flattening deformation increases. An increase in the deformation temperature will result in a decrease in the deformation resistance of the TC4 alloy and an increase in the ellipticity. Moreover, the effect of the deformation temperature, area reduction and wall thickness of the workpiece on the microstructure of the TC4 alloy hollow shafts formed by CWR was investigated. The degree of kink or globularisation of the strip alpha phase increases with the above parameters. The volume fraction of the beta phase increases with the deformation temperature. The microstructure is typically equiaxed when the deformation temperature is 950 °C.