Hot compression deformation behavior of Mg–Y–Zn alloys containing LPSO phase

The effect of the volume fraction of the long periodic stacking ordered (LPSO) phase on elevated temperature compressive deformation behavior is investigated using four types of Mg–Y–Zn alloys (Mg-0.4Y-0.2Zn, Mg–2Y–1Zn, Mg–5Y-2.5Zn, Mg–9Y–6Zn, where the numbers indicate at.%) produced by casting. The LPSO phase volume fraction is found to increase with increases in the concentrations of Y and Zn. The results obtained from compression tests at elevated temperatures reveal that the responses of these alloys to compression behavior, i.e., the stress vs. strain behavior, are changed by variations in the test conditions, such as the temperature and strain rate. The flow stress of the dilute solid-solution Mg-0.4Y-0.2Zn alloy containing a few volume proportions of the LPSO phase exhibits a small strain rate dependence on flow stress. In contrast, the flow stress clearly decreases with lower strain rate and higher temperature in the other three Mg–Y–Zn alloys, irrespective of the LPSO volume fraction. Observations of the deformed microstructures indicate that deformation twins are formed in the dilute alloy; however, the other three alloys show different microstructural features. Alternative for deformation twin formation, deformation kink bands are produced in these alloys; some of the existences of the LPSO phase (at least several dozens percent) are necessary to induce deformation kink band formation and to control the rate-controlling mechanism. Normalized plots obtained from previous hot compression testing together with the present results suggest that the volume fraction of the LPSO phase is unlikely to affect compressive deformation behavior.