Reversible plastic strain during cyclic loading–unloading of Mg and Mg–Zn alloys

Large hysteresis loops are observed during cyclic loading–unloading of Mg and Mg–Zn alloys. This is true for both tension and compression cycling, for grain sizes between 25 and 670 μm, and for Zn contents between 0 and 6 mass%. The loops are ascribed to anelasticity resulting from elastic { 1   0   1 ¯   2 } twinning. The anelastic strain increases with the strain and reaches a maximum at strains between about 1 and 2%. For a given total strain, the amount of anelastic strain increases with decreasing grain size, and decreases with increasing Zn content. The maximum observed anelastic strain is about 0.3% for pure Mg, decreasing with the solute content to about 0.2% for Mg–6 mass% Zn. The phenomenon is discussed in terms of the effect of solute content and grain size on the formation and stability of twins.