EFFECTS OF UNTWINNING AND {10(1)over-bar2} TWIN LAMELLAR STRUCTURE ON THE MECHANICAL PROPERTIES OF Mg ALLOY

Strengthening mechanism related to {10 (1) over bar2} twinning plays an important role in improving mechanical properties of Mg alloy. In this work, a hot rolled AZ31 Mg alloy sheets were subjected to dynamic plastic deformation (DPD) along the rolling direction and tests were interrupted at strains of 1%, 3% and 5% with the aim of introducing {10 (1) over bar2} twins, and then were annealed at 200 degrees C for 3 h to eliminate the dislocations. The tensile deformation behavior and the microstructural evolution of these pre-deformed samples containing {10 (1) over bar2} twin lamellar structure with the aim of analyzing effects of untwinning and {10 (1) over bar2} twin lamellar structure on the mechanical properties of materials were investigated. When subsequent tensile deformation is carried out along the DPD direction, untwinning causes a significant increase in the maximum flow stress. And the tensile yield stress and the maximum flow stress increases significantly with the volume fraction of twins. The texture hardening which is caused by the texture change attributable to untwinning plays an important role in improving mechanical properties of materials. When tension is carried out along the initial transverse direction, slip dominated plastic deformation and {10 (1) over bar2} twinning activity is restrained. The tensile yield stress increases slightly with pre-strain, suggesting that the hardening contribution of initial grain refinement by {10 (1) over bar2} twin lamellae is not very significant during deformation.