Fig. 1 Microstructures of the interface between MgGdYAg and MgAg produced by HPT: a SEM image, b close-up view of the yellow box in a, c bright-field TEM image, d high-resolution TEM image

Fig. 2 Chemical composition distribution near the interface of sandwich sample after HPT: a HAADF-TEM image, b-f EDS mappings in the region of white box in a

Fig. 3 Aging-hardening curves of MgGdYAg and MgAg samples treated at 200 °C

Fig. 4 Microstructures of MgAg layer of HPT sandwich after aging: a low-magnified bright-field TEM image, b high-magnified bright-field TEM image, c selected area diffraction pattern

Fig. 5 Microstructures of MgGdYAg layer of HPT sandwich after aging: a bright-field TEM image of γ″ phase view with g = 0002, b selected area diffraction pattern of γ″ phase, c corresponding simulated diffraction pattern of γ″ phase, d bright-field TEM image of β′ phase view with g=$\overline{1}010$, e selected area diffraction pattern of β′ phase, f corresponding simulated diffraction pattern of β′ phase

Fig. 6 HAADF-STEM images of the precipitations γ″ phase and β′ phase in MgGdYAg layer: a and b microstructures of γ″ phase viewed along [$1\overline{2}10$]Mg and [0001]Mg zone axes, respectively, c close-up image of γ″ phase viewed along [0001]Mg zone axis, d and e microstructures of β′ phase viewed along [$1\overline{2}10$]Mg and [0001]Mg zone axes, respectively, f close-up image of β′ phase viewed along [0001]Mg zone axis

Fig. 7 Mechanical properties of HPT sandwich, MgGdYAg and MgAg after aging: a uniaxial tensile engineering stress-strain curves, b true stress-strain curves, c strain-hardening (Θ) curves from tensile tests

Fig. 8 Schematic diagrams illustrating the evolution of microstructure of HPT heterostructure sandwich: a microstructure of interface area after deformation, b HDI stress in the interface

Fig. 9 Microstructures of HPT sandwich after tensile deformation: a bright-field TEM image and selected area diffraction pattern of MgAg, b, c high-magnified TEM images of MgAg viewed with g = $\stackrel{\mathrm{-}}{1}010$ and g = 0002, respectively, d bright-field TEM image and selected area diffraction pattern of MgGdYAg, e, f high-magnified TEM images of MgGdYAg viewed with g = $\stackrel{\mathrm{-}}{1}010$ and g = 0002, respectively