Room temperature equal-channel angular pressing of a magnesium alloy

Abstract

Equal-channel angular pressing (ECAP) of magnesium alloy Mg–3Al–1Zn (wt.%) has been carried out at room temperature by applying a back-pressure three times larger than the yield stress in a 90° die. In a single pass, the initial grain size of ∼10μm originating from twin-roll casting was reduced down to ∼3μm. {101¯2} tensile twins were observed by orientation imaging up to ∼40% volume fraction in grains that remained relatively high after ECAP. Regions with small grain size did not show twinning. The small lattice curvatures indicated that dynamic recovery/recrystallization took place during testing. The 90° ECAP deformation field was approximated by two-stage simple shear due to a large dead metal zone appearing at the outer corner of the die. Using this strain path, the viscoplastic self-consistent (VPSC) model was employed to model the texture evolution in the version where a parameter (α) tunes the interaction equation between a grain and the homogeneous equivalent medium. The textures were reproduced in good accord with experiments only if the α parameter corresponded to the Tangent VPSC model. Twinning was simulated in a quantitative way by introducing the volume transfer scheme in the VPSC model without employing a criterion for selection of the six possible twin variants.