An extruded Mg-Gd-Y-Ag alloy was subjected to simple shear extrusion (SSE) at 280 °C to obtain a refined microstructure, with a focus on examining microstructural evolutions through detailed EBSD analysis and TEM. The EBSD results revealed that the microstructures at the early stages of deformation contained large deformed grains with a significant fraction of low angle grain boundaries developed through dynamic recovery. Continuous dynamic recrystallization (CDRX) was dominant as deformation proceeded. Two kinds of CDRX grains were recognized considering their locations; “GB-type” grains, which formed in the vicinity of the pre-existing boundaries of the deformed grains, and “Core-type” grains, emerging within the interior areas. The EBSD exhibited pronounced misorientation gradients in the areas adjacent to pre-existing boundaries, and severe fragmentation into subgrains. At larger strains, the density of subgrain boundaries declined due to the massive progress of discontinuous dynamic recrystallization (DDRX). TEM investigations confirmed the emergence of globular Mg₅Gd-type nano-particles exclusively within the DRXed areas through dynamic precipitation, and the precipitation of nano-sized βʹ-phase, mainly within the larger deformed grains. Basal texture components of “type-I” and “type-II” were identified following 6 SSE passes. In the former case, the basal planes rearranged parallel to the shear planes with their poles aligned along the normal direction (ND) as a result of the activity of the basal slip system. In contrast, in the latter scenario, the basal poles were parallel to the transverse direction (TD) due to the 90° rotation of the workpiece between consecutive passes. The results of shear punch testing (SPT) indicated an increase in the shear strength, as the number of passes in SSE increased from 1 to 6. The improved mechanical response of the alloys after SSE was ascribed to various strengthening mechanisms, including the influence of low-angle grain boundaries (LAGBs), precipitation hardening and grain boundary strengthening.

Two severe plastic deformation (SPD) techniques of simple shear extrusion (SSE) and equal channel angular pressing (ECAP) were employed to process an extruded Mg−6Gd−3Y−1.5Ag (wt%) alloy at 553 K for 1, 2, 4 and 6 passes. The microstructural evolutions were studied by electron back scattered diffraction (EBSD) analysis and transmission electron microscopy (TEM). The initial grain size of 7.5 μm in the extruded alloy was reduced to about 1.3 μm after 6 SPD passes. Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP, with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation. The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization (DRX), so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries (HAGBs). It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods, where dissimilar basal plane texture components were obtained. The compression tests, performed along extrusion direction (ED), indicated that the compressive yield stress (CYS) and ultimate compressive strength (UCS) of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes. ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE. This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction (ED) of each SPD technique.