Formability enhancement in hot spinning of titanium alloy thin-walled tube via prediction and control of ductile fracture

The damage and fracture in hot spinning of titanium alloy is a very complex process under the combined effects of microstructure evolution and stress state. In this study, their dependences on processing parameters were investigated by an integrated FE model considering microstructure and damage evolution, and revealing the effects of microstructure and stress states on damage evolution. The results show that the inner surface of workpiece with the largest voids volume fraction is the place with the greatest potential of fracture. This is mainly attributed to the superposition effects of positive stress triaxiality and the smallest dynamic recrystallization (DRX) fraction and β phase fraction at the inner surface. The damage degree is decreased gradually with the increase of initial spinning temperature and roller fillet radius. Meanwhile, it is first decreased and then increased with the increases of spinning pass and roller feed rate, which can be explained based on the variations of β phase fraction, DRX fraction, stress state and tensile plastic strain with processing parameters. In addition, the dominant influencing mechanisms were identified and discussed. Finally, the thickness reduction without defect in the hot spinning of TA15 alloy tube is greatly increased by proposing an optimal processing scheme.