Fracture mechanism of Mg–3Al–1Zn sheet at the biaxial state with respect to forming temperatures

•Formability of AZ31 sheet was evaluated in the limit dome height test.•The limit height at 523 K increases 192% compared with one at room temperature.•Fracture mechanism changes from brittle to ductile.•Under the biaxial stretching state, dominant texture does not change.

Magnesium (Mg) sheet has been of great interest in automobile industries to make a light-weight design although it has low formability at the room temperature compared with steel sheets. It is required to elevate forming temperature to enhance the formability of Mg sheet, which enables increase of active slip systems in Hexagonal close packed (HCP) crystal structure. This paper demonstrates the effect of forming temperature on the formability of Mg–3Al–1Zn sheet, which is evaluated by the Limit Dome Height (LDH) test at temperature of 423 K, 523 K, and room temperature. The variation of dome heights depending on the forming temperature has been investigated to stand for its formability, and punch stroke and loads have been compared with each other. It has been tried to correlate the fracture mechanism with formability of AZ31 sheet with respect to the forming temperature by investigating the fracture surfaces with optical microscopy (OM) and orientation imaging microscopy (OIM) analyses.