Grain refining and fading mechanisms in a eutectic Al-Si alloy refined with Al-Nb-B

Resumo

© 2025 Elsevier B.V.This study investigates the grain refining efficiency and fading mechanisms of a 4Nb-1B-Al master alloy in an AA 413 eutectic aluminum-silicon alloy, comparing its performance to that of a conventional 5Ti-1B-Al refiner. The Nb-based refiner produced significantly finer grains—reducing the average grain size by approximately 200 µm after 15 min—and maintained superior performance even after 60 min. The enhanced refinement was attributed to the presence of Al₃Nb particles, which dissolve more slowly than Al₃Ti, as evidenced by thermal analysis and microstructural characterization. In unstirred melts, sedimentation and agglomeration of Al₃Nb and NbB particles were observed, indicating key fading mechanisms. These effects were mitigated by vigorous melt stirring and reduced holding times. Unlike Ti-based refiners, the Nb-based refiner showed no evidence of silicide formation (commonly referred to as grain poisoning). These results underscore the potential of Nb-based refiners for high-Si aluminum alloys, provided that processing conditions are optimized to minimize fading.

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