Stacking-fault mediated plasticity and strengthening in lean, rare-earth free magnesium alloys

A magnesium alloy with lean additions of Zn (1 wt.%) and Ca (0.3 wt.%), ZX10, and pure Mg were subjected to orientation-dependent micropillar indentation tests at ambient temperature. Single-crystalline micropillars of two different orientations were fabricated to activate extension and compression along the c-axis, respectively. For both loading conditions, ZX10 exhibits a strengthening increment by a factor of 2 to 2.5 compared to pure Mg along with plasticity enhancement. Correlative transmission electron back-scattered diffraction and transmission electron microscopy reveal that deformation in ZX10 proceeds by deformation twinning under c-axis extension, generating homogeneous activation of basal and non-basal slip at higher strains. In contrast, pure Mg displays deformation through tension twinning and basal slip. Pure Mg under c-axis compression deforms by basal dislocation-mediated massive sliding, while ZX10 reveals dual activation of basal 〈a〉 and pyramidal 〈c+a〉 dislocations. Mechanistically, the minute additions of Zn and Ca solutes modify the intrinsic stacking-fault energy, which accounts for the simultaneous strengthening and ductility enhancement. These findings highlight the beneficial impact of dilute additions of Zn and Ca in activating novel deformation pathways that are critical for designing rare-earth (RE) free high-strength, highly ductile magnesium alloys for structural and biomedical applications.