Understanding of variant selection and twin patterns in compressed Mg alloy sheets via combined analysis of Schmid factor and strain compatibility factor

Twinning is an important deformation mechanism for Mg alloys, which is intimately related to their mechanical behaviors, such as yield strength, strain hardening, ductility and so on. Therefore, a fundamental understanding of twinning behavior and mechanism under various conditions is essential for improving the mechanical properties of Mg alloys. This study aims to extend understanding the mechanism of {10-12} twin variant selection and twin patterns in compression of basal textured AZ31 Mg alloy sheet along transverse direction. Various twin patterns such as independent or intersecting multi-twins in a grain, paired twins in two neighboring grains, and twin chains across many grains were observed in the 3% compressed AZ31 sample. The variant selection of {10-12} twins in the various twin patterns were studied by a combined analysis of Schmid factor and strain compatibility factor, m′. Multiple twin variants can be formed in a grain and the non-Schmid twin variant could be induced by the impingement of a neighboring twin at grain boundary. Paired {10-12} twins are likely formed when the Schmid factors of both twins and their strain compatibility factor are very high. The paired twins can propagate throughout the grains and transfer to more neighboring grains (termed as twin-twin transfer behavior). Such continuous twin-twin transfer behavior across more than three neighboring grains results in the formation of twin chains. In addition, strain accommodation among the different twin variants in the same grain, and the orientation relationship between the paired twins and their common grain boundary direction are discussed. A comprehensive understanding of the twin patterns and variant selection was achieved by such a combined analysis of Schmid factor and strain accommodation factor.