Microstructure Evolution and Selection Behavior of Twin Variants of Mg-5Gd-3Y-0.5Zr Alloy during Secondary Deformation

A solution-treated (T4) Mg-5Gd-3Y-0.5Zr (named GW53K) alloy was subjected to 20%/0.002 s⁻¹ thermal deformation along the compression direction 1 at 350 °C followed by 20%/0.2 s⁻¹ deformation along the transverse direction 1 at room temperature. There were a few dynamic recrystallization grains, and twins appear in the primary deformation microstructure. Unlike it, large “twin clusters” and parallel broad tearing zones appeared in the secondary compression microstructure, which weaken the strength of texture. Through the analysis of twins occurred in the process of primary deformation and secondary deformation, it was known that when the twin was lenticular and had no interaction with surrounding grains, the selection of their variants followed to the maximum Schmid law. When the twins were cluster and interacted with adjacent grains, the selection of their variants did not follow to the maximum Schmid law, but the maximum geometric compatibility factor. The reason was that the activity of twins within adjacent grains activated the selection behavior of twin variant with low Schmid factor to coordinate stress concentration they generated. The {10-11} contraction twins appeared in the tearing zones, and it would be possible for them to further transform to shear bands.