In-situ observation of grain refinement dynamics of hypoeutectic Al-Si alloy inoculated by Al-Ti-Nb-B alloy

The grain refining behaviour of a novel Al-Ti-Nb-B alloy in Al-Si melt with low cooling rate was in-situ observed by synchrotron radiography. Nucleation and growth of alpha-Al dendrites in the near-isothermal Al-8Si-7Cu melts inoculated by Al-1.67Ti-3.33Nb-0.5B and Al-5Ti-1B and were investigated. The evolution of grain number density and dendrite growth rate of alpha-Al were quantitatively studied, with which the significant difference in nucleation potencies between TiB2 and (Ti,Nb)B-2 in Al-Si melt was understood. The superior grain refining efficacy of the Al-1.67Ti-3.33Nb-0.5B alloy owes to the sufficient amount of (Ti,Nb)B-2 particles potent for both epitaxial nucleation and free growth. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.