Enhanced Stretch Formability of Magnesium Alloy Sheet by Prestretching at Various Speeds at Higher Temperature

Prestretch deformation of 6.48% with various initial speeds (1mm/min, 101mm/min, and 100mm/min) was carried out at 723K to improve the formability of AZ31Mg alloy sheet. After prestretching, the (0001) basal texture weakened with increase in the speed owing to activation of nonbasal slips during deformation, while the yield strength and anisotropy decreased simultaneously. Owing to the basal texture weakening, the Schmid factors of the basal slips and strain-hardening coefficient increased, while the Lankford value decreased, enhancing the stretch formability of the AZ31Mg alloy sheet. In addition, the Erichsen value was improved from 2.48mm for the as-received alloy to 4.36mm for the sample prestretched at 100mm/min (an enhancement of 75.8%). This may provide a new approach for industrial production of Mg alloy sheets with weakened basal texture and improved formability by applying a smaller prestrain at higher temperature.