Effect of high-density twinning induced by electromagnetic drive forming on plastic deformation of AZ31B magnesium alloy

Compared to the quasi-static stamping forming (QSF), high-rate impact forming improves the plastic deformation ability of material at room temperature. However, improvement mechanism of formability of magnesium alloys via high-rate impact forming has rarely been evaluated to date. This study investigated the plastic deformation mechanism and microstructural evolution of AZ31B alloy under electromagnetic drive forming (EMDF). Compared to the QSF, the maximum forming height under EMDF increased by 31 %. The results showed that the number of twins increased in both QSF and EMDF samples as forming height increased, but the twin density in EMDF sample was higher. It indicated that the EMDF progress activated more twin behaviors, and transformed a single dislocation slip under QSF into a combination of dislocation slip and twinning under EMDF. Further, more twin nucleation consumed more dislocations at grain boundaries and offered added regions for dislocation pile-up. This both weakened the stress concentration and promoted the uniformity of stress concentration distribution, which suppressed the premature fracture. Moreover, more twins underwent deformation and more dislocations were activated in the EMDF sample. This not only expanded the source of deformation of the AZ31B alloy, but also coordinated the c-axis strain, thus also increasing plastic deformation ability.