Understanding the Influence of Alloying with Zn and Ca on Deformation Mechanisms and Fatigue Crack Initiation in Mg Alloys

While Mg alloys are promising for lightweight structural and biomedical applications, their widespread adoption is limited by poor fatigue resistance. Developing commercially viable alloys requires a thorough understanding of how alloying elements influence deformation mechanisms and subsequent crack initiation under cyclic loading. This study utilized fully-reversed, strain-controlled in-Scanning Electron Microscope (SEM) fatigue loading to characterize the microstructural evolution of Mg-2Zn, Mg-0.5Ca, and Mg-2Zn-0.5Ca (wt.%) alloys. Electron backscatter diffraction (EBSD) and EBSD-assisted slip trace analysis were employed to identify active deformation mechanisms and regions of heterogeneous strain accumulation that could act as sites for crack initiation. The results indicate the strong basal texture in Mg-2Zn promotes deformation via basal slip and deformation twinning. In contrast, Ca additions weakened the basal texture, enhancing non-basal slip and reducing twinning activity. While strain accumulated along grain and twin boundaries in all three alloys, the reduced twinning in the Ca-containing alloys resulted in fewer potential crack initiation sites at twin-boundary intersections. Furthermore, the activation of non-basal slip reduced the tensile-compressive strength anisotropy in Mg-0.5Ca and Mg-2Zn-0.5Ca. Altogether, these results demonstrate that the Mg-Zn-Ca system may serve as a cost-effective option for developing alloys with superior fatigue performance through texture modification.