Research On Large Strain Rolling Process Of AZ31Magnesium Alloy Sheets

Wrought magnesium alloy sheets have broad application prospects due to their excellent properties. However, the industrial applications of magnesium alloy sheets are greatly limited because of their poor formability owing to hexagonal close-packed crystal structure. Magnesium alloy sheets are conventionally produced by multipass rolling with small strain per pass accompanied by intermediate annealing, which is too inefficient and costly for commercial application. Therefore, it is important to investigate new technics which can produce high performance magnesium alloy sheets efficiently and inexpensively.Micro structure evolution and deformation mechanism of AZ31magnesium alloy sheets produce by large strain rolling (LSR) were studied in this paper. The result revealed that:magnesium alloy sheets with fine-grain microstructures can be processed via large strain rolling at temperature range of250-400℃, which had excellent mechanical properties although the grain size increased as the rolling temperature increasing. The highest yield strength (YS) and ultimate tensile strength (UTS) can be obtained at temperature of250℃and reduction of80%, which were267MPa and339MPa, respectively. AZ31magnesium alloy sheets with excellent mechanical properties (YS=309MPa, UTS=232MPa, elongation=26%) and average grain size of4.4μm were produced at temperature of400℃and reduction of80%, which also showed excellent thermal stability at200℃. At the deformation temperature of400℃, the critical strain for DRX was10%at the strain rate of50s-1, but50%at the strain rate of3s-1, therefore, the critical strain for dynamic recrystallization (DRX) can be reduced with the strain rate increasing at the same rolling temperature. Complete DRX microstructure can be obtained at300℃when reduction reached80%and strain rate higher than10s-1, otherwise, DRX grains can be finer with the strain rate increasing.Compared to conventional rolling technics, LSR can broaden rolling temperature range for magnesium alloy, which also can produce magnesium alloy sheets with homogenous fine grain structures and perfect mechanical properties.