Understanding grain refining and anti Si-poisoning effect in Al-10Si/Al-5Nb-B system

Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries, while the well-known Si-poisoning effect makes it difficult. Nbbased refiners offer an effective method to refine Al-Si casting alloys, but their anti Si-poisoning capability is far from being understood. In this work, the grain refining mechanism and the anti Si-poisoning effect in the Al-10Si/Al-5Nb-B system were systematically investigated by combining transmission electron microscope, first-principles calculations, and thermodynamic calculations. It is revealed that NbB2 provides the main nucleation site in the Al-10Si ingot inoculated by 0.1 wt.%Nb Al-5Nb-B refiner. The exposed Nb atoms on the (0 0 0 1) NbB2 and (1 -1 0 0) NbB2 surface can be substituted by Al to form (Al,Nb)B-2 intermedia layers. In addition, a layer of NbAl3-like compound (NbAl3) can cover the surface of NbB2 with the orientation relation of (1 -1 0 0)[1 1-2 0] NbB2//(1 1 0)[1 1 0] NbAl3'. Both of the (Al,Nb)B-2 and NbAl3' intermedia layers contribute to enhancing the nucleation potency of NbB2 particles. These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The study systematically investigated the grain refining mechanism and anti Si-poisoning effect in the Al-10Si/Al-5Nb-B system. It was found that NbB2 provides the main nucleation site in Al-10Si, while NbAl3-like compound covers the surface of NbB2, enhancing the nucleation potency of NbB2 particles.