Study On Twinning Behavior In Shear Deformation Of AZ31 Magnesium Alloys

Wrough magnesium alloys usually have strong texture,causing severe mechanical anisotropy and poor secondary forming ability,which limits its wide use.Twinning is an important plastic deformation mechanism for magnesium alloy,closely related to its mechanical properties and microstructure evolution during deformation.Therefore,it is necessary to systematically study the twin behavior in magnesium alloys under various deformation conditions.In this paper,nine kinds of AZ31 magnesium alloy plates with different initial texture were designed.Then,the twinning behavior in shear deformation at room temperature was systematically studied.The activaiton of twin variants in shear deformation was systematically analzyed using the generalized Schmidt factor and geometric compatibility factor.The effect of initial texture on twinning behavior in shear deformation and the underline variant selection mechanism were revealed.The main results are summarized as follows:Shear deformation was applied on the magnesium alloy sheets with nine different texture by using aspecial shear mould.The applied shear stress was decomposed into the components of tensile stress and compressive stress by coordinate transformation.With this,the activation of twinning in the magensium alloys with different texture can be approximately predicted.The twinning behavior in shear deformation was compared and statistically analyzed using the generalized Schmidt factor.This effectively explained the propensity and variant selection of twins in the magnesium alloy plates with different initial texture.It was found that most of the twins with negative Schmidt factor are located at the trigeminal boundary and grain interior,which are related to the local stress state.Based on experimental observation and crystallographic calculation,the variants of twin or twin pairs formed in shear deformation were statistically analzyed using the generalized Schmidt factor and geometric compatibility factor.This basically reveal the selection mechanism of these twin variants.