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The Geometrically Necessary Dislocation (GND) density was estimated from Electron Backscatter Diffraction (EBSD) data for an AZ31/Mg-0.6Gd (wt.%) hybrid material fabricated by high-pressure torsion (HPT) at room temperature through an equivalent strain range of ϵeq = 0.3–144 using Kernel Average Misorientation (KAM) and the Nye tensor approaches. The results show that generally the GND densities are significant at the beginning of the deformation (ϵeq = 0.3) and decrease in both alloys when ϵeq increases. The Mg-0.6Gd alloy exhibits a lower GND density due to rapid dynamic recrystallization. These results were compared to the GND densities measured in AZ31 and Mg-0.6Gd mono-materials processed separately by HPT under the same experimental conditions. In these mono-materials the GND densities increase with increasing equivalent strain up to 7 and then decrease with further straining. The Mg-0.6Gd and AZ31 regions of the hybrid material exhibit higher GND densities than the mono-materials particularly at low strain where the disc thickness and the bonding of the AZ31/Mg-0.6Gd interfaces cause more deformation heterogeneity in the hybrid material. It is shown that the GND density evolution as a function of ϵeq has the same tendency for the KAM and the Nye approaches but the average values are significantly higher with the Nye approach. An analysis suggests that the Nye approach overestimates the GND density of the Mg-based alloys. [ABSTRACT FROM AUTHOR]

High‐pressure torsion (HPT) processing is successfully applied to fabricate a novel hybrid material from separate discs of AZ31 (Mg–3Al–1Zn, wt%) and Mg–0.6Gd (wt%) alloys by straining through numbers of rotations, N, of 1/4, 1/2, 5, 10, and 20 turns at room temperature. The microstructure and texture are investigated near the bonding interface through the disc diameter using electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The microstructure exhibits two grain refinement regimes with the first occurring during an equivalent strain range, εeq, of ≈0.3–72 and the second during εeq from ≈72 to 517. The general texture changes from B‐fiber to Y‐fiber and C2‐fiber through the HPT processing. The resultant microstructures and textures of this hybrid alloy are examined separately for the AZ31 and Mg‐0.6Gd alloys and found controlled by the presence of twinning, slip systems, and second phases and the occurrence of different dynamic recrystallization mechanisms. [ABSTRACT FROM AUTHOR]

The evolutions of microstructure and texture and the corrosion behaviour of low light rare-earth containing Mg-1.4Nd and low heavy rare-earth containing Mg-0.6Gd and Mg-0.4Dy (wt.%) were evaluated and compared after processing by high-pressure torsion (HPT) and isochronal annealing at 250 and 450 °C for 1 h using electron backscatter diffraction (EBSD) and electrochemical tests in a 3.5% (wt.%) NaCl solution. The EBSD results show that dynamic recrystallisation (DRX) was restricted in the Mg-1.4Nd alloy which led to a heterogenous deformation microstructure whereas the Mg-0.6Gd and Mg-0.4Dy alloys exhibited a homogenous deformation microstructure formed mostly of equiaxed dynamically recrystallised DRX grains. The HPT processing caused the development of a deviated basal texture in the three alloys. A good thermal stability of the three alloys was noticed after annealing at 250 °C. By contrast, annealing at 450 °C led to a homogenous equiaxed microstructure and weakening of texture for the Mg-1.4Nd alloy and a heterogenous bimodal microstructure with a stable basal texture for the Mg-0.6Gd and Mg-0.4Dy alloys. The HPT-processed Mg–RE alloys exhibited an improved corrosion resistance due to grain refinement. Thereafter, the corrosion resistance of the Mg-0.6Gd and Mg-0.4Dy alloys decreased with increasing annealing temperature due to an increase in grain size while the corrosion resistance of the Mg-1.4Nd alloy was improved after annealing at 450 °C due to precipitation and texture weakening. [ABSTRACT FROM AUTHOR]

• Effect of HPT on the dissolution kinetics of Mg-0.6Gd alloy was examined using DSC. • After HPT, the dissolution peak decreased from 634 to 658 to 601–633 K. • After HPT, the activation energy decreased from 135 ± 9 to 118 ± 10 kJ/mol. • The dissolution mechanism was unaffected by HPT. The dissolution reaction kinetics were determined by differential scanning calorimetry (DSC) analysis for Mg-0.6Gd (wt.%) in an as-cast condition and after processing by high-pressure torsion (HPT) at room temperature for 20 turns. For the as-cast condition, the dissolution temperature was in the range of 634–658 K with an activation energy of 135 ± 9 kJ/mol. After HPT, the range of dissolution temperature decreased to 601–633 K, with a lower activation energy of 118 ± 10 kJ/mol. In both conditions, the Avrami and growth exponents are around 1.5, which suggests that the dissolved precipitates exhibit polyhedron-like morphology and that the dissolution process is dominated by bulk dissolution with a constant rate controlled by diffusion. [ABSTRACT FROM AUTHOR]

• E a of recrystallization of hybrid AZ31/Mg-0.6Gd was estimated as 112 ± 10 kJ/mol. • Mg 17 Al 12 and Mg 2 Zn phases in the AZ31 region obstructs the grain growth process. • The effect of Mg 5 Gd and Mg 12 Gd phases in the mg-0.6gd region is less evident. The recrystallization and grain growth activation energies of the hybrid AZ31/Mg-0.6Gd (wt.%) alloy were calculated using differential scanning calorimetry analyses and scanning electron microscopy, respectively, after fabricating by high-pressure torsion up to 20 turns and then subjecting to an isochronal annealing treatment from 423 to 723 K for 1 h. The DSC results show one exothermic peak belonging to the static recrystallization of the AZ31 region with an activation energy of 112 ± 10 kJ/mol. The grain growth kinetics for the AZ31 and Mg-0.6Gd regions were described by the Arrhenius equation. The calculation with a grain growth exponent equal to 4 gave values for the activation energies in both the AZ31 (146.2 ± 8.4 kJ/mol) and Mg-0.6Gd (90.9 ± 13.5 kJ/mol) regions. The present results reveal the heterogeneity of the thermal stability of the AZ31/Mg-0.6Gd hybrid material. [Display omitted] [ABSTRACT FROM AUTHOR]

The characterization of microstructure and texture development of binary Mg-0.3Ce (wt%) after equal-channel angular pressing (ECAP) processing via route Bc at 300 and 350 °C through 4 passes were investigated using electron backscatter diffraction (EBSD) measurements. The results demonstrated an effective grain refinement from millimeter range to 6.7 and 8.3 μm obtained after 4 passes at 300 and 350 °C, respectively. The grain refinement was obtained through dynamic recrystallization (DRX). At 300 °C, DRX occurred at low strain by twin-induced dynamic recrystallization (TDRX) and particle stimulated nucleation (PSN) mechanism and then converted with increasing strain to sub-grain development (SD) and grain boundary bulging dynamic recrystallization (GBBDRX). Besides, grain growth occurred during processing at 350 °C. The texture development strongly depends on the strain level, deformation temperature and DRX mechanisms. At 300 °C, a typical basal texture with a deviation of 40° towards extrusion direction was formed gradually up to 4 passes while a completely different texture was formed at 350 °C due to the large grain size. • Mg-0.3Ce alloy was processed by ECAP for 4 passes at 300 and 350 °C using route Bc. • Significant grain refinement was obtained after 4 passes due to DRX. • At low strain DRX occurred via TDRX and PSN mechanisms. • With increasing strain, SD and GBDRX mechanisms dominate the DRX processing. • Texture evolution strongly depends on the strain, temperature and DRX mechanisms. [ABSTRACT FROM AUTHOR]