Detwinning and Anneal-Hardening Behaviors of Pre-Twinned AZ31 Alloys under Cryogenic Loading

Detwinning behavior of a pre-twinned magnesium alloy AZ31 at cryogenic temperature was investigated, also with a focus on the annealing hardening behavior of samples with different fractions of pre-twins. Pre-compression along the transverse direction with strains of 1.7%, 3.0%, and 6.0% was applied to generated \(\left\{ {10\overline{1}2} \right\}\) twins. Mechanical behavior, microstructure, and texture evolution during subsequent tension were examined. Our results show that low temperature did not change the fact that detwinning still pre-dominated in the pre-twinned samples under reverse loading. However, a relatively harder migration of twin boundaries was found at cryogenic temperature. An annealing hardening of 27-40 MPa was observed in the pre-twinned samples, and such a hardening effect shows a close relation with the fraction of pre-twins or the level of pre-strains. The annealing hardening effect disappeared if the matrix was consumed by twins along with the increased pre-compression strains. The corresponding reasons for the annealing hardening behavior were discussed.