Effect of pre-induced twinning on microstructure and tensile ductility in GW92K magnesium alloy during multi-direction forging at decreasing temperature

Effect of pre-induced twinning on the microstructure evolution and mechanical properties of extruded Mg-9.26Gd-2.08Y-0.36Zr (GW92K) alloy have been investigated during multi-direction forging with large strains at decreasing temperature from 400 °C to 300 °C. The results showed that, whether there pre-induced twinning existing in the initial microstructure by pre-deformation or not, a mixed microstructure of residual coarse grains and notably refined grains formed under both conditions, combing with some residual coarse grains with less deformation inside grains and lots of dispersed nano-precipitates distributed along refined grain boundaries. However, a significant improvement with the tensile ductility was obtained by the pre-induced twinning in the former alloy. It was suggested that, the pre-induced twinning largely contributed to the grain refinement and lead to an increase in the ratio of fine grain structure which would be responsible for the better properties. Furthermore, during subsequent forging deformation in the pre-deformed sample, the grain refinement mechanism by gradual grain orientation rotation around the surface section in residual coarse-grains was a little different from that by the macro-shear deformation in the as-extruded condition.