Quantitative analysis of solidification of equiaxed grains in Al-Cu alloy refined by inoculant TiB2 particles with using time-resolved X-ray tomography

Abstract

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.