Effect of Basal Precipitates on Extension Twinning and Pyramidal Slip: A Micro-Mechanical and Electron Microscopy Study of a Mg-Al Binary Alloy

Abstract

Understanding the effects of basal precipitates on plasticity is of scientific interest and practical importance in the development of high-strength magnesium alloys. In this study, compression experiments are carried out on solution-treated and aged Mg-9wt.%Al binary alloy microcrystals pillars with two different compression orientations ( and ) to examine the effects of basal-precipitates on extension twinning and pyramidal slip, respectively. In the solution-treated, precipitate-free, samples, the propagation and thickening of single twins dominates, while in the aged microcrystals with Mg17Al12 basal-precipitates, multiple twins are observed suggesting a substantial increase in the stress required to propagate and thicken twins compared to nucleating twins. In addition, these basal precipitates are observed to be more effective than c-axis rod precipitates in impeding twin growth. In samples, the plate-like, Mg17Al12 precipitates are found to provide enormous strengthening under compression, compared to solution-treated samples, by hindering the motion of pyramidal dislocations. Further still, our comparative analysis suggests that pyramidal-slip/precipitate interactions, whether via bowing between or cutting precipitates, differ from one Mg alloy to another depending on their precipitate characters. Our findings offer insights into how manipulating precipitation in the design and processing of magnesium alloys can lead to superior mechanical properties.