Formability enhancement of 5052 aluminium alloy sheet in electromagnetic impaction forming

Electromagnetic impaction forming of 5052 aluminium alloy sheets using a V-shaped die and a conical die was performed. The conventional quasi-static forming limit curve (QS-FLC) is obtained according to the linear loading condition, which can only describe linear strain paths. However, it cannot accurately evaluate the formability of electromagnetic impaction forming, especially strain paths that have become highly non-linear. In this study, the formability of electromagnetic impaction forming, which considers a bilinear strain path and a continuous highly non-linear strain path, was investigated. The conventional QS-FLC is no longer suitable to evaluate the formability of electromagnetic impaction forming. Therefore, modified FLCs were established in strain space that follow bilinear strain paths and continuous non-linear strain paths. The actual formability improvement was compared with the modified FLC. The maximum safe strain of bilinear strain paths near the sidewall of V-shaped specimens increased in formability by approximately 30% at the discharge voltage of 20 kV compared with conventional QS forming. The maximum safe strains near the apex of the conical specimens increased in formability by approximately 100% at the same discharge energy. It should be noted that the increase in formability above the modified FLC is a conservative estimate, because the limit strains at the necking location were not known in the electromagnetic impaction forming. The influencing factors of the formability improvement of 5052 aluminium alloy sheet in electromagnetic impaction forming were also discussed.