Influence of the electric pulse on springback during stretch U-bending of Ti6Al4V titanium alloy sheets

摘要

Electrically assisted stretch U-bending tests have been conducted in this research to analyze the influence of electrical parameter duty cycle cycle on the springback of Ti6Al4V sheets. It is found 30% duty cycle brings about 50% increase in residual height of split angle of U-bending specimen compared with that obtained in room temperature. Meanwhile, 30% duty cycle causes additional 13% effect on springback relief than that treated in 10% duty cycle at the same temperature, which indicates elevated temperature alone is insufficient to account for overall decrease on springback during the treatment of electric current. Subsequent electrically assisted stress relaxation test under the same condition gives further explanation on the decrease of springback in short period numerically. Microstructure evolution observed in both tests illustrates grain growth along with dislocation motion activated by thermal expansion results in stress softening in the duty cycle less than 20%. As for the duty cycle of 30%, the precipitated alpha' phase reveals that the accelerated phase transformation alpha -beta can provide additional stress drop and such observation is also certified by hardness investigation conducted in this research.