Microstructural evolution and formability of Ti−6Al−4V alloy sheet during electropulsing-assisted bending

Abstract

The electropulsing-assisted bending test was carried out on Ti−6Al−4V alloy sheet with the effective current density of 0−3.2 A/mm2 and duty ratio of 10%−70%. The results show that the bending forming displacement increased from 9.15 to 15.60 mm with increasing effective current density from 0 to 2.4 A/mm2. The crack changed to be shallow and small at the same time. Besides, the springback angle decreased as the effective current density increased at the bending displacement of 8 mm. Duty ratio also affected bending angle, where 30% duty ratio led to the lowest bending angle of 135.0°. The thermal stability temperature increased with increasing effective current density and varied non-monotonically with duty ratio. In addition, grain coarsening, {0001} texture strengthening and sub-grain development were observed during electropulsing-assisted bending. The electropulsing decreased dislocation density and accelerated dislocation rearrangement, the rearranged and piled-up dislocation inside α grains promoted sub-grain structure formation, which improved the formability. The contribution of athermal effect made the low-temperature formability of Ti−6Al−4V alloy comparable to that at high temperature.