Comparative study on dislocation slip activity of the solid-solution and as-aged Mg-9.8Gd-3.5Y-2.0Zn-0.4Zr (wt%) alloys during ambient temperature quasi-in-situ compression

Abstract

In order to understand the effect of precipitation on the slip activities of Mg-Gd-Y-Zn-Zr alloys, the dislocation slip activities of solid-solution and as-aged alloys during ambient temperature quasi-in-situ compression were quantitatively investigated by electron backscattered diffraction (EBSD)-assisted slip trace analysis. First, slip trace analysis of both alloys showed that the β' precipitates reduced the frequency and number of grains with slip traces significantly, resulting in a pronounced precipitate-hardening behavior. At 11% strain, the aging treatment reduced the proportion of prismatic <a > slip and second-order pyramidal <c + a > slip by 4.6% and 9.3%, respectively, while the proportion of basal slip increased by 13.9%, indicating that the precipitate-hardening effect of non-basal slip was stronger than that of basal slip. Moreover, based on the slip trace statistical analysis and TEM images of the sheared β' precipitates, the critical resolved shear stress (CRSS) increments of different slip modes caused by the prismatic plate-shaped β' precipitates follow the order of Δτ pyramidal-2 > Δτ prismatic > Δτ basal . Also, we found the plastic inhomogeneity of solid-solution alloy during ambient temperature deformation can increase the propensity of non-basal dislocation slip and promote non-Schmid behaviors. However, a large number of fine β' precipitates dispersed in the as-aged alloy can effectively alleviate the plastic inhomogeneity in the grain-scale range during ambient temperature deformation. Further, TEM dislocation analysis under two-beam conditions shows that the abundant solute RE atoms in the solid-solution Mg-Gd-Y-Zn-Zr alloy contribute to the activity of second-order pyramidal <c + a > dislocations. Therefore, we conclude that the changes in slip activity caused by the precipitation of Mg-Gd-Y-Zn-Zr alloys are mainly attributed to β’ precipitates, plastic inhomogeneity, and solute RE atoms. • The β' precipitate-hardening effect for pyramidal-2 slip is the strongest, followed by prismatic and basal slip. • The dispersed β' precipitates effectively alleviate the plastic inhomogeneity and promote the Schmid behavior. • The solute RE atoms contribute to the activity of pyramidal-2 < c + a > dislocations.