Static Recr Ystallization Behavior Of Magnesium Alloy Containing {10（1-）2} Twins

Twinning constitutes an important deformation mechanism of Mg alloys, The role of twinning in plastic deformation involves strain accommodation along the c-axis direction, reorientation of the twinned regions and relaxing stress concentrations. In general, contraction twins are observed at high strain, and easy to form inhomogeneous deformation regions, so contraction twins are the dominant recrystallization nucleation sites. In contrast, extension twin forms at the early stage of deformation, producing homogeneous areas, which can not serve as the effective nucleation sites. The present work mainly study the static recrystallization behavior of AZ31 Mg alloy. The hot rolled plate and extruded rod of AZ31 suffer compression test at room temperature. XRD and EBSD analysis are applied to characterize the microstructures and texture evolution of AZ31 samples before and after annealing. The effect of static recrystallization on texture evolution is discussed. The main conclusions are as following:① In the 2.8% TD pre-compression sample without ND pre-compression, annealing at 350℃ for 2 h is necessary to totally remove the {1012} twins and a severe grain coarsening happens. The mechanism of recrystallization is strain induced boundary migration（SIBM）. SIBM involves the motion of pre-existing boundaries to consume the deformed structure. The driving force for this mechanism is a difference in dislocation density on either side of the boundary.② In the 5.5% ND pre-compression followed by 2.8% TD recompression sample, the 5.5% ND pre-compression does not change the main deformation mode during the subsequent compression along the TD and hardly reduces the compressive plasticity along the TD. The stored energy generated by the 5.5% ND pre-compression results in extensive nucleation at grain boundaries and enhances the thermal mobility of {101_<sub>2} twin boundaries. A fully recrystallized structure with the refined grains is achieved by an annealing at 250℃ for 1 h. Orientations of the {101_<sub>2} twins before annealing are well kept in the recrystallized structure after annealing 250 ℃ for 1 h.③ In the different compression strain along TD samples of hot rolled plate AZ31, as the pre-strain increases from 2% to 5%, the volume fraction of extension twins increases from 2.60 μ m to 4.23 μ m. During annealing 450 ℃ /4h, the thermally activated boundary migration happens.④ In the different compression strain along TD samples of extruded rod AZ31, as the pre-strain increases, both the volume fraction and lamella thickness of extension twins increase, the grain subdivision effect by twin lamella also enhances. The thermally activated boundary migration of {101_<sub>2} twins exhibits a strong twin thickness effect. If the thickness of twin is much narrower than that of matrix, the twin tends to be consumed by the matrix during annealing at high temperature. However, when the thickness of twin is much wider than that of matrix, the twin prefers to consume the matrix. The consumption of twin by matrix leads to a transformation from the twin orientation into the matrix orientation and vice versa.