On the room temperature deformation mechanisms of a Mg-Y-Zn alloy with long-period-stacking-ordered structures

We present a transmission electron microscopy study on the room temperature deformation mechanisms in a Mg97Y2Zn1 (at.%) alloy with long-period-stacking-order (LPSO) phase. The alloy consists of alpha-Mg matrix with platelet-shaped LPSO precipitates 3-5 nm thick and interdendritic LPSO (18R structures) phase grains. The interdendritic LPSO phase was found to deform either by kink-banding in conjunction with basal < a > slip or by basal < a > slip and the formation of dislocation walls. No orientation dependence of these different deformation modes was observed. The alpha-Mg matrix deforms by basal < a > slip and pyramidal < c + a > slip. No twinning was observed in the alpha-Mg matrix during room temperature deformation. The elastic modulus mismatch between alpha-Mg matrix and LPSO plates is suggested to be the main source for activating non-basal dislocations. The combination of the soft alpha-Mg matrix strengthened by LPSO precipitates and harder "bulk" interdendritic LPSO grains is suggested to contribute to the well-known good mechanical properties of Mg-LPSO alloys at room temperature. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.