The effect of hot rolling on the microstructure, texture and mechanical properties of twin roll cast AZ31Mg

In this study, a commercially available twin roll cast AZ31 Mg sheet was hot rolled at 400 °C to investigate the influence of rolling parameters (speed and percent thickness reduction) on microstructure, texture and mechanical properties. As compared to the twin roll cast condition, the microstructure of the successfully rolled materials was much finer and relatively less bimodal but contained profuse twinning and varying fractions of dynamically recrystallized grains. The extent of dynamic recrystallization (DRX) during rolling was found to be significantly influenced by percent thickness reduction. In the parameters investigated here, the rolling speed had a weak effect on DRX. The results showed that hot rolling strengthened the weak basal texture of the twin roll cast material and in addition to necklace grain formations at grain boundaries, DRX inside the twins was also identified as a key recrystallization mechanism. Mechanical testing revealed that at room temperature hot rolling improved the yield strength with retention of limited tensile ductility (<15%). However at 200 °C, the rolled material exhibited more a balanced mechanical properties with large tensile elongations. Microstructural analysis of the failed tensile tested specimens showed that the deformation behavior was dependent on grain size and crystallographic texture.