Dynamic recrystallization of the H- and O-tempered Mg AZ31 sheets at elevated temperatures

Uniaxial tensile properties influenced by the dynamic recrystallization (DRX) behavior of the partially strain-hardened magnesium AZ31 sheets (H24) containing scores of twins were investigated and compared to those of fully annealed ones (O) with absence of twins. For this purpose, a series of uniaxial tensile tests were carried out for the H24 and O materials at temperatures ranged from room temperature to 300 °C and at strain rates between 10−3 and 10−1 s−1. At 150 and 200 °C, the H24 material exhibited higher yield strength without much loss in elongation compared to those of the O material; this trend was attributed to the continuous DRX along or around grain boundaries as well as extensive twin-aided DRX inside grains. In addition, the post-deformation hardness value of the H24 material showed higher than that of the O material. On the other hand, at higher temperatures of 250 and 300 °C, it was observed that twins shown in the H24 material were disappeared even prior to deformation, resulting in the similar grain structure and mechanical property values to those of the O material, e.g., discontinuous DRX associated with grain boundary bulging. Finally, the initiation of DRX was rationalized in terms of microstructure morphology, deformation temperature and strain rate, and then modeled in the context of strain hardening rate analysis. A comparison of experimental results and predictions for both H24 and O materials showed that the model can provide a reasonable prediction of critical strain to initiate DRX.