Influence of Microstructure and Mechanical Properties on Formability in High Strain Rate Rolled AZ31 Magnesium Alloy Sheets

High strain-rate rolling (≥ 10 s⁻¹) has been successfully employed to produce AZ31 magnesium alloy sheets to a high reduction of 82% with a fine grain structure in a single pass. The rolled sheets inevitably undertake various forming processes such as press and deep forming in the fabrication stage. To investigate the formability, the Erichsen tests were carried out on high strain rate rolled AZ31 magnesium alloy sheets at room temperature. The relationship among mechanical properties, microstructure and formability were investigated. The crack behavior during Erichsen tests was also studied. It was found that the formability was related to the lowest in-plane tensile strengthen and dislocation density of initial microstructure. The competitive relationship between micro-crack and twinning/shear bands would also influence the formability of high strain rate rolled magnesium alloy sheets. Deformed shear band with substaintial twins prohibits the crack extension and enhances strengthen of materials in front of crack tip.