Surprising increase in yield stress of Mg single crystal using long-period stacking ordered nanoplates

Mg-Zn-Y ternary alloys containing the long-period stacking ordered (LPSO) phase exhibit superior mechanical properties. This is believed to be originating from the LPSO phase acting as the strengthening phase. However, we first clarify that the mechanical properties of the matrix Mg solid solution in the Mg/LPSO two-phase alloy are significantly different from those of pure Mg. The yield stress of a Mg99.2Zn0.2Y0.6 single crystal (matrix Mg solid solution) is almost the same as that of an LPSO singlephase alloy. This is ascribed to the formation of thin stacking-fault-like defects, named LPSO nanoplate. In Mg99.2Zn0.2Y0.6, kink-band formation is induced in the same manner as that in the LPSO phase in deformation, resulting in high strength accompanied with increased ductility. Our results suggest that the strengthening mechanism of the Mg/LPSO two-phase alloy must be reconsidered depending on the microstructure. Furthermore, the results suggest that new ultrahigh-strength Mg alloys, which have much lower Zn and Y contents but the mechanical properties are comparable or superior than the present Mg/LPSO two-phase alloys, are expected to be developed via the appropriate control of LPSO nanoplate microstructures. (c) 2021TheAuthor(s). PublishedbyElsevierLtdonbehalfofActaMaterialiaInc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Automated summary

Ternary alloys containing long-period stacking ordered (LPSO) phase exhibit superior mechanical properties due to the strengthening effect of LPSO phase. The matrix Mg solid solution in Mg/LPSO two-phase alloy has different mechanical properties compared to pure Mg, with the formation of LPSO nanoplate contributing to high strength. The results suggest that new ultrahigh-strength Mg alloys with lower Zn and Y contents but comparable or superior mechanical properties are expected to be developed by controlling LPSO nanoplate microstructures.