Tailoring the microstructure and mechanical properties of LPSO-containing Mg–Ni cast alloy by yttrium addition

Abstract

The effect of yttrium addition on the evolution of phases, grain refinement, and mechanical behavior of Mg-0.5Ni cast alloy was investigated. It was observed that while the base alloy contained a eutectic structure containing α-Mg and Mg2Ni, in the Y-containing alloys, the long period stacking ordered (LPSO) structures and Mg24Y5 phase appeared at the expense of the eutectic structure. The dendrite arm spacing (DAS) was significantly refined, so that adding 0.5 and 2 at% Y led to the refinement of DAS from 141 to 56 and 22 μm, respectively. Accordingly, hardness, tensile and shear strength were improved, being successfully represented by the Hall-Petch-type relationships in terms of DAS. The highest elongation to failure in tensile tests was obtained at 0.5 % Y addition, which was ascribed to the refinement of microstructure and partial replacement of the deleterious α-Mg + Mg2Ni eutectic structure by the LPSO phase. However, further addition of Y led to the formation of intergranular interconnected network of LPSO structure with deteriorated ductility. Therefore, the best strength-ductility synergy was obtained for the Mg99Ni0.5Y0.5 alloy, as evaluated by the tensile toughness. Finally, the tensile and shear properties were correlated according to the von-Mises criterion.

Keywords

• Magnesium alloys
• LPSO structures
• Grain refinement
• Mechanical properties
• Hall-petch relationship