2. Materials and experimental proceduresThe Mg8.2Gd4.6Y1.5Zn0.4Zr alloy was prepared by semi-continuous casting. Commercially pure Mg and Zn were used. Gd and Y were added as Mg–30wt.%RE master alloys, and Zr was added as Mg–30wt.%Zr master alloy. The ingot with dimensions of Φ162 mm×4000 mm was casted at 760 °C after homogeneous stirring. Next, the ingot was homogenized at 510 °C for 16 h, after which it was extruded at 400 °C with an extrusion speed of 0.2–0.4 mm/s and an extrusion ratio of 25.The microstructures of the alloys in different states were observed by optical microscopy (OM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The surfaces for OM and SEM observation were etched using a solution of 4% HNO3 with ethanol. Disc samples (3 mm diameter) for TEM and HRTEM analyses were ground to 50 μm thicknesses followed by ion beam thinning (GATAN, PIPS 695). The microstructures were observed and analyzed using an FEI Tecnai F20 electron microscope operated at 200 KV. The mean grain size was obtained from the EBSD result. The hardness was tested by a HXS-1000AKY hardness tester, and five measurements were taken to calculate an average value. The tensile specimens were tested using an MTS material testing machine.