This study investigates the combined effects of pre-deformation and double aging treatment on the precipitation behavior and mechanical properties of AA2026, a precipitation-strengthened Al-Cu-Mg alloy. A 5% cold tensile strain was applied prior to aging to introduce dislocations, which served as preferential nucleation sites and enhanced solute diffusion via pipe diffusion mechanisms. The double aging treatment decouples the nucleation and growth stages through a two-step thermal cycle, enabling more precise control over precipitate formation. Microstructural analysis using DSC and HR-TEM revealed that the double aging treatment led to finer and more uniformly distributed GPB zones and S'/S phases, while effectively suppressing overaging. Compared to conventional single aging, the double aging treatment significantly improved the alloy's strength-ductility balance. These enhancements are attributed to the synergistic interaction between dislocation-assisted nucleation and controlled thermal processing. The proposed approach offers an effective strategy to optimize the mechanical properties of AA2026 for structural applications.

The evolution of microstructure and texture during high-temperature deformation was investigated in a Mg-11 wt.% Pb magnesium alloy with different initial textures. Plane strain compression tests were conducted at 723 K with a strain rate of 5.0 × 10^-2 s^-1 up to a true strain of -1.0, using specimens prepared to exhibit distinct initial texture components along the normal, transverse, and rolling directions. The deformed microstructures and texture characteristics were analyzed by electron backscatter diffraction (EBSD), pole figures, and orientation distribution functions. Despite the significant differences in the initial textures, all specimens exhibited a gradual convergence toward a dominant basal texture with increasing strain. EBSD analyses revealed progressive grain refinement during deformation, indicating the occurrence of dynamic recrystallization, which promoted the preferential development of basal-oriented grains. The basal texture components $\{0001\}<10{{\bar{1}}0>$ and $\{10{\bar{1}}0\}<11{\bar{2}}0>$ were consistently observed in all specimens at higher strains, suggesting that these orientations represent stable texture components under the present plane strain deformation conditions.

The grain boundary diffusion process (GBDP) is am effective technique used to enhance the coercivity of Nd-Fe-B magnets by coating the magnet surface with heavy rare earth elements such as Tb and Dy in the form of hydrides or fluorides, followed by heat treatment to enable diffusion into the interior along the grain boundaries. These diffusion sources are typically employed as high-purity heavy rare earth hydrides or fluorides, and multiple repetitive processing steps are generally required to control oxygen content. In some cases, additional elements such as Cu, Al, and Ga are incorporated to reduce the melting point of the diffusion material or to improve its wettability at the grain boundaries during heat treatment, thereby increasing diffusion depth and uniformity. In this study, a high-energy ball milling process was adopted to simplify the fabrication procedure of heavy rare earth grain boundary diffusion materials. The diffusion powder was prepared via high-energy ball milling, and its morphology and particle size distribution were analyzed for characterization. Considering the phase diagram and melting temperature, the composition of the heavy rare earth diffusion material was designed as Dy₇₀Al₂₀Cu₁₀. A cast master alloy was first coarse-crushed to below 200 ㎛, and subsequently refined to below 10 ㎛ through high-energy ball milling. Morphological and particle size analyses of the coarse-crushed Dy₇₀Al₂₀Cu₁₀ powder and the powder produced by high-energy ball milling revealed irregular particle shapes in both cases. Compared to the coarse-crushed powder, the average particle size of the high-energy ball-milled powder was significantly reduced from 103 ㎛ to 8.44 ㎛, corresponding to a reduction of more than 90%. Compositional and melting point analyses were conducted for both the coarse-crushed and ball-milled Dy₇₀Al₂₀Cu₁₀ powders. XRF and SEM-EDS results indicated that both powders were consistent with the target composition without significant deviation. Furthermore, DTA measurements of the high-energy ball-milled powder showed a melting temperature of 688.84℃, confirming that the ball milling process did not adversely affect the compositional integrity and that the prepared powder possessed a melting point suitable for grain boundary diffusion processing.

The objective of this study is to investigate the effect of long-term artificial thermal aging on hardness variation in dissimilar metal welds (DMWs) used in nuclear power plant components. Such DMWs are widely applied to the joints between reactor pressure vessel (RPV) nozzles and piping systems and are typically composed of a combination of ferritic low-alloy steels and austenitic stainless steels. To simulate the material degradation behavior that may occur during long-term operation of nuclear power plants, artificial thermal aging tests were conducted. The specimens were aged in an electric furnace at 600℃ for up to 10,000 h, and the tests were interrupted at several aging intervals to analyze the evolution of material properties with aging time. It is well known that variations in mechanical properties, such as hardness, are closely associated with microstructural evolution and degradation occurring during prolonged exposure to high-temperature environments. In the present study, it was observed that the hardness distribution varied significantly depending on the location within the dissimilar metal weld, including the base metal, heat-affected zone (HAZ), and weld metal. In particular, the observed hardness variations were found to be strongly correlated with microstructural factors such as twinning, grain evolution, precipitation behavior, phase transformation, and residual stress. Therefore, this study systematically investigates the microstructural evolution occurring during long-term thermal aging and elucidates the mechanisms responsible for hardness variation. The findings of this work provide fundamental insights for the long-term reliability assessment of dissimilar metal welds in nuclear power plant components.