Effect of B addition on the formation of Fe-rich phases in Al-Si-Fe alloys

• Published in: Journal of alloys and compounds 2023-01, Vol.930, p.167426, Article 167426
• Main Authors: Song, Dongfu, Zhao, Yuliang, Jia, Yiwang, Huang, Guangyao, Zhang, Zhibo, Zhou, Nan, Li, Xintao, Zheng, Kaihong, Fu, Yanan, Zhang, Weiwen
• Format: Article
• Language: English
• Subjects: Al-Si alloy; Aluminum base alloys; Aluminum oxide; B addition; Casting; Eutectic reactions; Eutectic temperature; Fe-rich phase; Ferrous alloys; First principles; First-principles calculations; Grain refinement; Iron; Mathematical analysis; Microscopy; Nucleation; Optical microscopy; Phases; Silicon; Solidification; Supercooling; Synchrotron radiation; Synchrotron X-ray radiography; Synchrotrons; X-ray radiography
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.167426

Boron (B) is an effective grain refiner in Al-Si alloys, but the mechanism responsible for the effect of B on the formation and growth of Fe-rich phases is still in debate. In this paper, we used in-situ synchrotron X-ray radiography, combined with optical microscopy, scanning electron microscopy, thermodynamics and first-principles calculations, to study the influence of B on the nucleation and growth of Fe-rich phases in Al-7Si-xFe (x = 1.2–3.0) alloys. The results showed that B had an excellent influence on the grain refinement of Al-7Si-1.2Fe alloys, but it had no obvious effect on the morphology and distribution of Fe-rich phases due to the eutectic reaction to form Al-AlB2. B had a certain refining effect on primary Fe-rich phases in Al-Si-Fe alloys with high Fe content (≥2.36 wt. %), but it cannot completely inhibit the formation of these plate-like Fe-rich phases. The in-situ synchrotron X-ray radiography results showed that the addition of B significantly reduced the formation temperature of primary Fe-rich phases. First-principles calculations showed that the adsorption energy of B on the nucleation sites , e.g., α-Al2O3 (0001), was significantly higher than that of Fe, which inhibited the nucleation of the primary Fe-rich phase above the Al-AlB2 eutectic temperature and promoted its undercooling of nucleation. Furthermore, many α-Al nuclei formed during the transition to the Al-AlB2 eutectic; their subsequent growth hindered the development of the primary Fe-rich phase. The results of this study provide insights for designing new recycled Al-Si alloys and fundamental knowledge of Fe-rich phase modification by B addition. •B on the Fe-rich phases modification in Al-Si-xFe alloys are established.•B addition increases the nucleation undercooling of Fe-rich phases.•B refines the size of Fe-rich phases in high Fe-containing alloys.•The adsorption energy of B on the surface of α-Al2O3 (0001) inhibits nucleation of Fe-rich phase.