Al-Ti-B微細化剤におけるTiB₂凝集体サイズと微細化能の関係

抄録

In order to reduce the risk of the casting defects, fine grains are required in the aluminum DC casting process. It is commonplace to use the grain refiner as a means of obtaining the desired grain structure. Typical grain refiners are Al-Ti-B system. In this study, TiB₂ agglomerates in Al-Ti-B grain refiner were observed by multiscale X-ray computed tomography (CT), which has Micro-CT and Nano-CT. The grain size of cast sample with grain refiner was calculated by grain size prediction model with TiB₂ agglomerate size distribution. The predicted grain size and measured grain size showed good agreement in case that assuming free growth will initiate on larger TiB₂ agglomerate prior. Additionally, the TiB₂ agglomerates at the center or boundary of α-Al grains were observed by multiscale X-ray CT. The TiB₂ agglomerates at the center of grain were larger than these at the grain boundary. Therefore, the assumption of free growth will initiate on lager TiB₂ agglomerates was estimated to be valid. From these results, it was estimated that the grain refinement effectiveness of grain refiner was varied by the TiB₂ agglomerate size distribution, and it can be calculated by grain size prediction model with TiB₂ agglomerate size distribution.