Microstructure and Mechanical Properties of Mg–8Y–2Ho–2Zn Alloy with Long Period Stacking Ordered Phase

Abstract

In this study, microstructures, phase compositions, phase morphologies of the as-cast and as-extruded Mg–8Y–2Ho–2Zn (wt%) alloys were investigated by optical microscope, scanning electron microscope, energy-dispersive spectrometer, transmission electron microscope and X-ray diffraction. The mechanical properties at room temperature and elevated temperatures were evaluated by tensile test. The primary secondary phases in the as-cast alloy are 18R-type long period stacking ordered (LPSO) phase. After extrusion, the microstructure mainly consists of considerable fine dynamically recrystallized (DRX) grains, the long strip 18R-type LPSO-phase at grain boundary along the extrusion direction and the fine lamellar 14H-type LPSO-phase in the interior of DRX grains. When the temperature is increased, the strength of the alloy is reduced, but the elongation progressively rises. The as-extruded alloy shows higher strength and larger elongation than the as-cast alloy at each test temperature. The superior mechanical properties of the as-extruded alloy are ascribed to various strengthening mechanisms induced by co-addition of Y and Ho element, e.g., solid solution strengthening, fine-grain strengthening and strengthening of fine LPSO-phase.