Effect of rolling speed on microstructure and mechanical properties of AZ31 Mg alloys rolled with a wide thickness reduction range

Hot rolling with three different rolling thickness reductions (20%, 40% and 70%) was carried out by single rolling pass on AZ31 Mg alloy sheets at three different rolling speeds varying between 3.5 and 12.1 m/min. The evolutions of the microstructure and mechanical properties of the hot rolled samples were critically examined. The results showed that twinning was the dominant deformation behavior during hot rolling at small rolling reduction and secondary twinning was the main way of twinning in this rolling condition. At high rolling speed, dynamic recrystallization can be activated and further enhanced by increasing thickness reduction. As the microstructure was refined, both strength and ductility of the samples were improved by dynamic recrystallization. While no obvious dynamic recrystallization was investigated during hot rolling at low rolling speed, twinning was further enhanced by increasing thickness reduction at this speed, resulting in an increase in yield strength and a remarkable reduction in ductility.