Shae Kwang Kim

A production-scale Al–8.5 wt% Mg alloy cast by the ECO-processing route was processed by high-pressure torsion (HPT) at 6 GPa and room temperature for one and ten turns. Microstructure and hardness were characterized at the center, mid-radius, and edge of the disks by spherical-indexing electron backscatter diffraction (SI-EBSD) and Vickers microhardness, and the entire disk was examined by X-ray diffraction (XRD). The as-received lattice parameter (0.4091 nm) corresponds to ≈9 at% Mg in solid solution and remained unchanged after HPT within ±0.7 at% Mg, with no β-Al3Mg2 detected within XRD detection limit; the supersaturated solid solution thus survived deformation. HPT refined the grain size from ≈28 µm to ≈0.20 µm, with high-angle boundary fractions of 87–94% after ten turns. The XRD crystallite size (≈65 nm) remained several times smaller than the grain size, indicating a finer dislocation substructure within the grains, and the dislocation density reached 2.1 × 1014 m–2. After ten HPT turns, the hardness increased from 95 to 259 HV at the edge without strain softening, while the center remained ≈18% softer. Linear superposition of solid-solution, grain-boundary, and dislocation strengthening accounts for ≈83% of the edge hardness. After the solid-solution contribution is subtracted, the alloy still lies above the literature data for HPT-processed Al–Mg alloys at comparable grain sizes, although part of this offset may reflect different grain-size measurement methods. These results are consistent with retarded dynamic recovery in the high-Mg solid solution, which allows a dislocation substructure to be retained but delays homogen

High-Mg Al–Mg sheets offer strong solid-solution strengthening, but dynamic strain aging can produce Portevin–Le Chatelier (PLC) instability and surface markings. This study examines how annealed microstructure modifies PLC behavior as matrix Mg increases. Al–6Mg, Al–9Mg, and Al–12Mg sheets were produced by horizontal twin-roll casting followed by identical homogenization, cold rolling, and O-temper annealing. X-ray diffraction, room-temperature tensile testing at a nominal engineering strain rate of 1 × 10⁻³ s⁻¹, digital image correlation (DIC), and electron backscatter diffraction were used. The XRD-estimated matrix Mg concentration increased from 6.2 to 9.3 and 11.9 wt.%. Deformation changed from early PLC serrations in Al–6Mg (critical strain, εc = 0.019) to delayed serrations in Al–9Mg (εc = 0.131) and no detectable macroscopic serrations or recurrent PLC bands in Al–12Mg. At 15–20% strain, the interval-averaged DIC strain-transfer deviation index was 1.10, 0.84, and 0.30 for Al–6Mg, Al–9Mg, and Al–12Mg, respectively. Al–12Mg nevertheless achieved a mean ultimate tensile strength of 406 MPa and 24.5% total elongation. Its stable response coincided with a coarse (103.0 μm), nearly fully recrystallized structure, low high-angle grain-boundary length density (44.8 mm⁻¹), and maximum grain orientation spread of 0.63°. The results indicate that matrix Mg establishes dynamic-aging potential, the intragranular state influences PLC initiation, and grain/boundary architecture governs whether local strain bursts develop into macroscopic bands. Thus, Al–12Mg demonstrates an O-temper route to strong, ductile sheet with improved deformation-surface stability under the investigated condition.

This study investigates the influence of Si content (1–4 wt. %) and T5/T6 heat treatments on precipitation behavior, electrical conductivity, and mechanical properties of a Ca-modified high-Mg Al–5Mg–xSi (Almag5–xSi) alloy system. Thermodynamic and kinetic analyses indicate that increasing Si accelerates Mg₂Si precipitation by reducing nucleation barriers, while trace Ca (nominally 0.02 wt.%) promotes heterogeneous nucleation via Al₄Ca/Ca–Si clusters, refining eutectic Mg₂Si from lamellar to fibrous morphology and enhancing intragranular β″ precipitation. TEM–FFT–IFFT analysis confirms that T6 treatment produces dense, coherent β″ (Mg₅Si₆) precipitates, with partial β′ (Mg₉Si₅) formation in Si-rich alloys. Ca modification induces multi-oriented β″ nucleation and suppresses coarsening. The electrical conductivity increases with Si content and is higher after T6, reaching 48.3±0.5% IACS for Almag5–3Si owing to the near-stoichiometric Mg/Si ratio and solute depletion. The yield strength increases with Si, peaking at 361.7±1.5 MPa in Almag5–4Si, while the ultimate tensile strength reaches 368.3±1.3 MPa. The maximum ductility (13.3%) is observed in Almag5–2Si owing to the stable β″ precipitates. Notably, the Ca-modified Almag5–2Si alloy outperformed the Ca-free Al–5Mg–2Si counterpart, showing a superior strength–conductivity–ductility balance due to refined dense β″ precipitation and early β′ formation. Overall, Si and Ca synergistically optimize strength, conductivity, and ductility.

High-Mg containing aluminum alloy sheet (Al-9Mg) was produced by horizontal twin-roll casting (TRC), yielding a ~6 m strip with uniform thickness and a centerline segregation-free microstructure. After homogenization, 75% cold rolling, and full annealing, the sheet exhibited a fully recrystallized grain structure (~40 μm) and an excellent strength–ductility balance (YS ≈ 162 MPa, UTS ≈ 343 MPa, elongation ≈ 25%). Serrated flow was investigated by correlative full-field DIC and in-situ tensile EBSD. PLC activity initiated at ε ≈ 0.13 and manifested as propagating B-type stretcher-strain marks inclined ~55–60° to the rolling direction. In-situ EBSD revealed that macroscopic PLC bands originate from intragranular shear bands (~45° traces) that preferentially developed in grains oriented between ⟨001⟩ and ⟨101⟩, where {111}⟨110⟩ slip showed high Schmid factor, low Taylor factor, and low initial KAM/GND. Progressive straining produced strong substructure refinement: the LAGB boundary-length density (2–15°) increased from 3.34 to 153.29 mm⁻¹ and the mean KAM rose from ~0.18° to ~0.39°, while GOS classification shifted from fully recrystallized to predominantly deformed. Texture changes remained modest (PF max 4.28→4.34 m.r.d.; ODF max 15.6→17.5 m.r.d.), indicating that PLC deformation is governed primarily by orientation-dependent slip localization and was accommodated by rapid substructure refinement.

This study investigates the influence of Si content (1–4 wt. %) and T5/T6 heat treatments on precipitation behavior, electrical conductivity, and mechanical properties of a Ca-modified high-Mg Al–5Mg–xSi (Almag5–xSi) alloy system. Thermodynamic and kinetic analyses indicate that increasing Si accelerates Mg₂Si precipitation by reducing nucleation barriers, while trace Ca (0.002 wt.%) promotes heterogeneous nucleation via Al₄Ca/Ca–Si clusters, refining eutectic Mg₂Si from lamellar to fibrous morphology and enhancing intragranular β″ precipitation. TEM–FFT–IFFT analysis confirms that T6 treatment produces dense, coherent β″ (Mg₅Si₆) precipitates, with partial β′ (Mg₉Si₅) formation in Si-rich alloys. Ca modification induces multi-oriented β″ nucleation and suppresses coarsening. The electrical conductivity increases with Si content and is higher after T6, reaching 48.3±0.5% IACS for Almag5–3Si owing to the near-stoichiometric Mg/Si ratio and solute depletion. The yield strength increases with Si, peaking at 361.7±1.5 MPa in Almag5–4Si, while the ultimate tensile strength reaches 368.3±1.3 MPa. The maximum ductility (13.3%) is observed in Almag5–2Si owing to the stable β″ precipitates. Overall, Si and Ca synergistically optimize strength, conductivity, and ductility.