Investigation of influence of direct-current pulses on springback during V-bending of AZ31B magnesium alloy sheet

The influence of electrical parameters pulse frequency (f) and peak current density (J) on the springback of AZ31B magnesium alloy sheet was studied through electrical pulse-assisted (EPA) V-bending at 373 K. To do this, a current pulse generator and a bending setup were designed and manufactured. In the test, controlling variable method in which only f or J can be changed while other testing parameters were kept constant was adopted. The results show that at the same testing temperature 373 K, varying f or J, different springback angle can be deserved: the higher the f or J, the smaller the springback angles. In addition, at 373 K, increase of effective current also leads to evident reduction in springback angle. It demonstrates that athermal effect of the electrical pulses exists in EPA V-bending of this material. To understand the mechanism of the EPA V-bending, microstructure evolution in the bent part was studied through optical microscope. The results indicate that the electrical parameters f and J not only decrease the grain size at the bent part, the higher the f or J, the finer the crystals but also decrease the number of twinning crystals during EPA V-bending. Both the decrease of grain size and the number of twinning crystals are considered to contribute to springback reduction.