Thermal Stability and Mechanical Properties of Extruded Mg-Zn-Y Alloys with a Long-Period Stacking Order Phase and Plastic Deformation

Abstract

Lightweight Mg alloys with excellent shock-absorption properties are being actively adopt‐ ed for use in electronic information devices and automotive parts [1]. For such structural ap‐ plications, Mg alloys need to have adequate ductility, thermal stability, and strength. However, Mg alloys often exhibit low ductility and low tensile yield strength at room tem‐ perature and above as a result of a scarcity of slip systems in their hexagonal close-packed structures [2]. Effective ways of improving the ductility and tensile yield strength of Mg al‐ loys include grain refinement [3] and control of the texture [4]; these techniques promote prismatic slips and facilitate the creation of large plastic deformations. Recently, alloys of Mg with transition metals (TMs), such as Co, Ni, Cu, or Zn, and rare-earth (RE) metals, such as Y, Gd, Tb, Dy, Ho, or Er, have been found to show superior mechanical properties to those of other Mg alloys [5,6]. A characteristic of these Mg–TM–RE alloy systems is the for‐ mation of a long-period stacking order (LPSO) phase in as-cast materials and/or after heat treatment. In the present study, we examined the annealing properties, tensile properties, thermal stability, and rolling workability of high-strength extruded Mg96Zn2Y2 alloys. Mg96Zn2Y2 alloy contains an LPSO phase as a secondary phase in the dominant α-Mg phase [5,6]. In general, Mg alloys with LPSO phases are known to have greatly enhanced mechani‐ cal properties, whereas their ductility can be maintained only by extrusion and/or plastic de‐ formation treatments of the cast metal. It has been suggested that kink deformations in the LPSO phase and microstructural refinement in the α-Mg phase occur during extrusion de‐ formation [7]. The tensile yield strength, microstructure, fatigue properties, and thermal sta‐