Grain Refinement Mechanism of Al-5Ti-1B Master Alloy by Ab Initio Calculations

Abstract:

To exactly understand the grain refining mechanism of α-Al by the Al-5Ti-1B master alloy, the structural properties of α-Al/solid-TiB₂ (S/S) and liquid-Al/solid-TiB₂ (L/S) interfaces were studied using the first-principles method. Different ordered structures were formed on the interfaces with different terminations of TiB₂ (0001) surface, which determines the nucleant potency of TiB₂. The heterogeneous nucleation of α-Al on the B-terminated surface is frustrated by an AlB₂-like structure formed at the interface. In contrast, a five-layer quasi-solid region with stacking sequence of fcc-Al (111) planes forms on the Ti-terminated TiB₂ (0001) surface, which is the basis of successful heterogeneous nucleation of α-Al. Moreover, when redundant Ti solute being added into the liquid Al region of Ti-terminated liquid-Al/TiB₂ interface, the quasi-solid Al region further extends until entire solidification. The reason for using the Al-5Ti-1B master alloy rather than TiB₂ powders as the commercial refiner in Al industry lies in two aspects: the excessive Ti atoms in the master alloy could guarantee sufficient Ti chemical potential to form Ti-terminated surface of TiB₂, and the redundant Ti solute in inoculated melts could facilitate the growth of quasi-solid Al region at the solid/liquid interface.

• Periodical: Materials Science Forum (Volumes 794-796)
• Pages: 746-751
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.794-796.746
• Online since: June 2014
• Authors: Han Long Zhang*, Yan Feng Han, Jun Wang, Yong Bing Dai, Bao De Sun
• Keywords: Ab Initio Simulation, Al-Ti-B Master Alloy, Grain Refinement, Interface

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