The effect of pre-compressive strain on the fatigue life of the AZ31 magnesium alloy

In the previous work, Horibe, one of the authors of this study, indicated that in the AZ31 magnesium alloy, the twinning-detwinning process dominated the plastic strains with greater amplitude, whereas dislocation slips dominated the lower plastic strains, which appeared bi-linear in the Manson-Coffin curve (M. Matsuzuki, S. Horibe, MSEA 504 (2009) 169-174). This alloy is used in a fatigue environment after plastic forms. However, the influence of pre-compression on either the fatigue life or deformation mode (slip or twinning) has not been clarified. In this study, we demonstrate that through pre-compression, more twinning tends to change the S- N curve from bi-linear to linear by changing the deformation mode, which results in shortening the fatigue life at lower stress levels. Furthermore, pre-compression promotes natural aging and increases yield stress. Higher yield stress increases the remaining twinning after the first fatigue test cycle, which also decreases the fatigue life.