Effect of pre-strain levels and high temperature annealing on the formability of AZ31 Mg alloy thin sheet during stretch deformation

Abstract

Pre-compression deformation at different strain levels (1.58%, 3.32%, 5.38% and 7.78%) along transverse direction (TD) are conducted to introduce (10–12) tensile twins at room temperature. The static recrystallization process is induced by annealing at 450 °C for 2 h. Then the stretch deformation is conducted at room temperature to investigate the fracture and formability of Mg sheet. The c-axis of grains tiltes from normal direction (ND) to transverse direction (TD) due to the tensile twins; however, the TD-rotated texture is inherited by the new recrystallized grains. The grains grow up and the size increases gradually as the pre-strain levels increasing. Due to the rotated orientation, the basal slips are favored and a larger Schmid factor is obtained on the pre-strained samples. The yield strength reduces, and the ductility increases. Besides, the strain hardening coefficient (n-value) increases and Lankford value (r-value) decreases at the same time. Owing to the TD-rotated orientation, the increased n-value and reduced r-value, the stretch formability is enhanced greatly. The Erichen value (IE-value) increases largestly from 2.83 mm to 5.74 mm which improves by 102.8%.