Suppressed transformation of compression twins to double twins in Mg by activation of non-basal slip

Abstract

The transformation of compression twins (CT) to double twins (DT) is studied in a dual-textured Mg-6.5%Zn(wt.) alloy during deformation along the extrusion axis. After 7.3% compression, 85% of CT are transformed to DT. This ratio drops to 22% and 36% during tension although the applied stresses and strains in tension were much higher. The Schmid factor of the actual DT variants was very low (and often negative) in tension and compression and could not explain the differences in DT activity. It is shown that the suppressed CT→DT transformation during tension is accompanied by the activation of 〈a〉 non-basal slip -rather than 〈a〉 basal slip- which presumably hinder the transformation because the dissociation of 〈a〉 basal dislocations is necessary to nucleate and grow extension twins in primary CT. These findings point out an effective strategy to suppress DT by activating 〈a〉 non-basal slip, which may be useful to design Mg alloys with high ductility.