The Deformation Behavior Of AZ31 Magnesium Alloy By Equal Channel Angular Extrusion

Equal Channel Angular Extrusion (ECAE) was performed to refine the microstructure of AZ31 magnesium alloy with the initial sample size of 20mm×20mm×80mm at the temperature from 160℃to 250℃. Commercial Non-linear finite-element (FEM) software MSC.Marc was applied to simulate ECAE process and investigate the non-homogeneous deformation during ECAE. The microstructure was examined by optical microscopy(OM),and scanning electronic microscopy(SEM), and textures were investigated by X-ray Diffraction(XRD) and EBSD (Electron back scattered diffraction). Tension-compression deformation behavior of the as-extruded magnesium alloy and ECAEed ultra-fine grain magnesium alloy at ambient temperature and elevated temperatures were investigated. And the effects of microstructure on the deformation behavior of extruded and ECAEed AZ31 alloy were discussed. The conclusions were given as follows:The FEM simulation and grid experiment showed that there was inhomogeneity metallic macro flow during ECAE, and the stress concentrations were observed locating at the shear core and the end stage.. The microstructures in the sample along horizontal and vertical appeared non-homogeneous distribution after one ECAE pass, and the grains was finer in the outer than that in the center when observing from the cross section. The microstructure gradient was ascribed to the asymmetric stress in ECAE. At given further ECAE deformation, the microstructure gradient was weakening. Ultra-fine and homogeneous microstructure for AZ31 alloy was obtained by ECAE 4 or more passes.There was reverse Hall-Petch relationship for the yield stress and grain size of ECAE AZ31 Mg alloy comparing with the as-extrusion. Strong tension-compression asymmetry was observed in the as-extrusion alloy but for ECAE alloy was weakened. ECAE alloy also exhibits strain rate sensitivity, and the strain rate sensitivity factor would be increased with process temperature increasing.The average grain size was 20μm for the as-extrusion alloy and it had a typical ring basal texture, the main deformation models for the as-extrusion AZ31 alloy at room temperature were basal slip and twinning, which resulted in the strong tension-compression asymmetry. In the case of ECAE, the average grain size was 1～2μm, texture was randomized relatively, which resulted in remarkably decrease of twin volume fraction under compression loading and then the tension-compression asymmetry in ECAE AZ31 alloy is weaker. The calculated apparent activation energy in the ECAE AZ31 was approached the activation energy of grain boundary diffusion Mg alloy, which provide evidence to support that the deformation on grain boundaries have important role on the deformation behavior, and the possible grain boundaries sliding (GBS) have contribution for the reverse Hall-Petch relationship and strain rate sensitivity in ECAE alloy.