Understanding The Role of Alloying on Low Cycle Fatigue Behavior in Mg Alloys

In this study the role alloying elements such as Ca and Zn on low cycle fatigue (LCF) behavior and fatigue lifetime were investigated using a methodology employing in-Scanning Electron Microscopy (SEM) loading, quasi-in-situ loading, and electron back scatter diffraction (EBSD). Fully-reversed, strain-controlled LCF experiments were performed on unalloyed Mg, Mg-2Zn (wt. %), Mg-0.5Ca (wt.%) and Mg-2Zn-0.5Ca (wt. %). Total strain amplitudes ranging from 0.4-1.2% were employed to understand the role of plastic strain on deformation mechanisms and fatigue lifetime. Stress-strain hysteresis loops and strain life curves were constructed based on the Coffin-Manson relation to quantify and compare the fatigue behaviors. The results suggested that different plastic deformation mechanisms were active and led to shorter fatigue lives in Mg-2Zn and Mg-2Zn-0.5Ca compared to unalloyed Mg. In-SEM loading and EBSD experiments showed that twinning and detwinning were dominant deformation mechanisms in unalloyed Mg and Mg-2Zn while non-basal slip influenced fatigue behavior in Mg-2Zn-0.5Ca.