Research on long-period-stacking-ordered phase in Mg–Zn–Dy–Zr alloy

The effects of Zr partial substitution for Mg on the microstructures of as-cast and heat-treated Mg94Zn1.5Dy4.5 alloy were investigated, respectively. It is found that the effect of Zr on the microstructural refinement of as-cast Mg–Zn–Dy–Zr alloys varies with Zr content, that is, microstructural refinement is not obvious when Zr content is between 0.17 at.% and 0.35 at.% while significant when Zr no more than 0.17 at.%. In addition, Zr remarkably affects the formation of Mg8ZnDy eutectic phases and LPSO phases in as-cast Mg–Zn–Dy–Zr alloys, with increasing of Zr content, the area fraction of LPSO phases decreases while the area fraction of Mg8ZnDy eutectic phases increases. When the content of Zr in Mg–Zn–Dy–Zr alloys reaches up to 0.35 at.%, the LPSO phases disappear and there are only Mg8ZnDy eutectic phases and α-Mg phases in the alloys. Furthermore, Mg8ZnDy eutectic phase can transform to LPSO phase by heat treatment.

► A new Mg8ZnDy phase is found in as-cast Mg–Zn–Dy–Zr alloys.
► Mg8ZnDy phase can transform into LPSO phase during heat treatment.
► Zr affects the formation of Mg8ZnDy phase and suppresses the LPSO phase.
► As-cast Mg–Zn–Dy alloy is refined by adding Zr, the critical value is 0.17 at.%.