The microstructures of the as-rolled magnesium alloy subjected to dynamic plastic deformation along the rolling direction have been investigated.Mostly one {1012} twin variant or a twin variant pair is activated in a grain,leading to a parallel {1012} twin lamellar structure.At the stage of twinning-dominated deformation(ε<~8%),lamellar thickness decreases significantly with strain,from 5.55 to 2.49μm.The evolution of lamellar thickness during deformation is directly related to {1012} twin activity.When plastic strain is greater than ~8%,the twin lamellar structure disappears because the volume fraction of twins almost saturates at a value of ~90%.
Effect of {10-12} twins on the mechanical properties of magnesium alloy has received considerable research interest. A hot-rolled AZ31 Mg alloy sheet was subjected to dynamic plastic deformation with the aim of introducing {10-12} twin lamellar structure. It has been found that higher strength and better ductility are obtained when tensile loading is perpendicular to the c axis of twin region of the twin lamellar structured sample, indicating that the plasticity improvement caused by twins depends on the special strain path. The fracture morphology of the twin lamellar structured sample shows a dimple fracture mode under tensile loading perpendicular to the c axis, while the cleavage fracture with river pattern has been observed in other fractured samples. Above experimental results indicate that the interaction of dislocations and twin lamellae may play an important role in improving mechanical properties of Mg alloy.
