By conducting In-situ XRD measurement during tensile deformation while oscillating the tensile tester, it was possible to measure the change in dislocation density of a pure aluminum alloy having coarse grains with the grain size of 20 μm. In the coarse-grained material, the dislocation density during tensile deformation changed through four regions, as in the case of the fine-grained material. Since the dislocation multiplication start stress was very low at 22MPa, the elastic deformation region was very short. Thereafter, the dislocations multiplied rapidly, but when the stress and dislocation density reached 33 MPa and 1.57×10¹⁴m^-2, respectively, the dislocation multiplication rate was greatly reduced. This is considered to be due to the low dislocation density required to progress the deformation by plastic deformation in coarse-grained aluminum.

Time-resolved X-ray tomography was performed to observe three-dimensional equiaxed-grain structure in Al-15mass%Cu alloy refined by inoculant TiB₂ particles. The time resolution of as short as 0.5 s was achieved by using a pink X-ray beam at a beamline BL28B2 of SPring-8. A filtering method using a phase field model was used for improving quality of reconstructed images, and consequently motion of equiaxed grains were observed in-situ. The time and spatial resolutions allowed to analyze the three-dimensional microstructural evolution. Nucleation events of α-Al preferably occurred in the melt of the bottom part, where the temperature was lower. The dendritic grains were formed during floating after the nucleation because of the buoyancy force. The floating equiaxed grains were stacked due to the floating, and the solid fraction of the stacked regions ranged from 0.11 to 0.19. The observations suggested that the coherency point of dendritic grains was less than 0.2. The observations also showed the grain motion influenced the formation of equiaxed grain structure.

This paper proposes a technique for evaluating the nucleation sequence and grain refinement phenomena during solidification of a metallic alloy. Time-resolved and in-situ transmission imaging using a monochromatized X-ray in a synchrotron radiation facility, SPring-8, showed wave-like nucleation events, in which nucleation sequentially occurred along the temperature gradient, in an Al-4mass%Si alloy with addition of TiB₂ (Al-3mass%Ti-1mass%B alloy). The position and time of nucleation events were measured to analyze the nucleation wave. The wave motion, which was calculated from the measured data, was used to evaluate the difference of nucleation temperature for each dendritic grain from the wave front. The standard deviation of the temperature difference in the Al-4mass%Si alloy with TiB₂ particles was evaluated to be as small as 0.25 K. The addition of TiB₂ reduced the standard deviation to more than one tenth. This study shows that the dispersion or the standard deviation is a representative figure for evaluating the potency of nuclei.

This study investigated cluster formation in the early stages of natural aging in Al-1.04 mass%Si-0.55 mass%Mg alloys by soft X-ray XAFS measurements and first-principles calculation. XAFS measurements at the Mg-K and Si-K edges were carried out at the BL27SU beamline at SPring-8. It was found that the absorption edge energies changed as aging proceeded. Density functional theory (DFT) calculations were used to determine the valence electron densities near Si and Mg atoms and to simulate the Si-K and Mg-K edge spectra for some cluster models. On the basis of the results, it was demonstrated that Si and Mg atoms formed clusters in four stages (I-IV) during natural aging. In stage I, Si-vacancy pairs, Mg-vacancy pairs, and a combination of both were formed. In stage II, vacancies were released from the clusters formed in stage I. In stage III, Mg-vacancy pairs were included in the clusters. In stage IV, the clusters coarsened through the release of vacancies. These results indicate that soft X-ray XAFS, which is capable of identifying individual elements, has the ability to provide information on such clusters.