Fig. 1. (a) SEM image and (b) EBSD orientation map with inverse pole figure colouring scheme of coarse-grained Mg-Gd-Y-Ag-Zr-Ce alloy. (c) EBSD orientation map and (d) TEM-BF image of fine-grained Mg-Gd-Y-Ag-Zr-Ce alloy. (e, f) Grain size distribution histogram of coarse-grained and fine-grained Mg-Gd-Y-Ag-Zr-Ce alloy, respectively. (g) Mg (Gd, Y, Ag, Ce) particle size distribution histogram of the fine-grained Mg-Gd-Y-Ag-Zr-Ce alloy.

Fig. 2. Bright-field TEM images of the CG alloys aged for 30 h observed from (a) <10$\bar{1}$0>α, (b) <0001>α zone axis. Bright-field TEM images of the CG alloy aged for 300 h observed from (c) <10$\bar{1}$0>α, (d) <0001>α zone axis. (e-l) The statistical results of precipitate size.

Fig. 3. (a) Bright-field TEM images of the Mg-Gd-Y-Ag-Zr-Ce alloy during the cooling process after extrusion. (b) A magnified TEM image of the square area in (a). (c) A high-resolution TEM image of the basal precipitate γ′′.

Fig. 4. (a) Low magnification bright-field TEM images of as-extruded Mg-Gd-Y-Ag-Zr-Ce alloy aged for 60 h. The bright-field TEM images of the nanoscale basal plate-shaped γ′′ precipitates observed from [0001]α zone axis (b), and the prismatic plate-shaped precipitate β′ observed from [11$\bar{2}$0]α zone axis (c).

Fig. 5. TEM identification of the Mg (Gd, Y, Ce, Ag) particles for (a) bright-field image, (b) HRTEM images with the Fourier transform embedded. (c) EDX-STEM spectrum acquired from one of the areas marked with a circle in (a).

Fig. 6. HAADF STEM images of three different zones in the extruded Mg-Gd-Y-Ag-Zr-Ce alloy.

Fig. 7. Schematic diagrams of microstructures in (a) solutionized, (b) aged at 200 °C for 300 h, (c) extruded and (d) extruded following by ageing at 200 °C for 60 h.

Fig. 8. (a) The variation of strength as a function of ageing time at 200 °C in CG and FG alloys. (b) Engineering stress-strain curves of FG and CG alloys. (c) Room temperature true stress-strain curves showing strain-rate jump tests of FG specimens at different strain rates ranging from 10-4 to 10-2 s-1.

Fig. 9. Representative SEM images of the fracture surface in CG and FG alloys. (a) Secondary electron (SE) images and (b) backscattered electron (BSE) images of CG alloys. (d) SE images and (e) BSE images of FG alloys. Side view of SEM images of fractured tensile CG (c) and FG (f) specimens.

Fig. 10. Typical microstructure images of the FG alloys. (a) weak-beam dark-field image with diffracting vector of g =$\bar{2}$110α and (b) two-beam bright-field image. Electron beam direction is close to [0$\bar{1}$10]α.