Study on necking defects, microstructure and mechanical properties of TC4 alloy by cross wedge rolling

The TC4 alloy is an ideal material for the lower control arm of military vehicles due to its low density and high strength. The TC4 alloy lower control arm formed by cross wedge rolling (CWR) has high innovation and application value. Based on the Arrhenius equation, the constitutive equation for the α + β two-phase region of the TC4 alloy was established and applied to the finite element model (FEM). The effect of process parameters on the necking defects of TC4 alloy shaft parts formed by CWR was studied and verified by experiments. Additionally, the effects of process parameters on the microstructure and mechanical properties were investigated. The results showed that the softening effect of TC4 alloy makes the rolled workpiece prone to necking defects. Different forming and stretching angles changed the axial forces between the die and the workpiece and affected the relative diameter reduction (RDR) of TC4 alloy rolled parts. The axial force and contact area F2 between the die and the rolled workpiece increase with the increase in the area reduction, which further has a significant effect on the RDR. The increase in deformation temperature causes the metal to flow less in the axial direction and more in the circumferential direction, and thus reduces the RDR. Moreover, deformation temperature and area reduction have a significant effect on the volume fraction of the primary α phase (fα_e), the morphology and mechanical properties of the α phase. The strength properties of TC4 alloy can be improved by interleaving equiaxed α phase with disordered secondary α phase and increasing the fα_e. The grain refinement and strength properties can be improved by increasing the area reduction to more than 30%.