The cyclic frequency sensitivity of low cycle fatigue (LCF) behavior of the AZ31B magnesium alloy

Magnesium alloy components would be potentially subjected to cyclic loads resulting in a fatigue. The low cycle fatigue (LCF) is usually characterized by cyclic plastic deformation which is affected by strain rate. In this study, the LCF behavior of an AZ31B magnesium alloy was investigated at different cyclic frequencies (0.01 Hz, 0.1 Hz, 2.0 Hz and 5.0 Hz) and strain amplitudes (0.75%, 1.0%, 2.0% and 4.0%) under asymmetric loading. It was found that the alloy exhibits a cyclic hardening behavior at all selected strain amplitudes. However, the cyclic frequency exerts an evident effect on the cyclic hardening rate. As the frequency increases, the cyclic hardening rate decreases. In addition, the LCF life increases with increasing cyclic frequency. Based on the discussion of deformation mechanisms, it was confirmed that high strain rate favors {10−12}〈10–11〉 twinning–detwinning and inclines to restrict dislocation slip, resulting in the low cyclic hardening rate and the long LCF life at the high cyclic frequencies.