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Development of Al–Nb–B master alloy with high Nb/B ratio for grain refinement of hypoeutectic Al–Si cast alloys

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Al–Nb–B master alloy has been regarded as a promising grain refiner that can reduce grain size of hypoeutectic Al–Si casting alloys. However, its grain refinement performance remains to be improved. In this work, the grain refinement efficacy of Al–Nb–B master alloy is significantly enhanced by modifying the Nb/B ratio through thermodynamic calculation. An Al–Nb–B master alloy with optimum Nb/B ratio of ~ 10:1 provides a fully equiaxed structure across the sections of the Al–10Si and commercial Al–9Si–0.08Ti alloys with an average grain size below 220 μm. The phenomenon is attributed to the existence of NbAl3 and the higher number density of NbB2 at the Nb/B ratio of ~ 10:1, which offers sufficient active nucleating sites to promote the formation of smaller grains. Moreover, the segregation behavior of Si atoms and interfacial energies after doping Si are investigated by first-principles calculations, and the results reveal that Si tends to segregate to the NbAl3/α-Al interface, whereas grain refining potency of NbAl3 for Al remains unchanged. This study has implications for strategic design of Al–Si cast alloy with fine and equiaxed grain structure inoculated by grain refiner.
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METALS & CORROSION
Development of Al–Nb–B master alloy with high Nb/B
ratio for grain refinement of hypoeutectic Al–Si cast
alloys
J. Xu
1
,Y.Li
1
,B.Hu
2
, Y. Jiang
1
, and Q. Li
1,
*
1
Materials Genome Institute and Shanghai Institute of Materials Genome and State Key Laboratory of Advanced Special Steels and
Shanghai Key Laboratory of Advanced Ferrometallurgy and School of Materials Science and Engineering, Shanghai University,
Shanghai 200444, China
2
China Science Lab, General Motors Global Research and Development, 56 Jinwan Road, Shanghai 201206, China
Received: 21 April 2019
Accepted: 9 August 2019
Published online:
19 August 2019
ÓSpringer Science+Business
Media, LLC, part of Springer
Nature 2019
ABSTRACT
Al–Nb–B master alloy has been regarded as a promising grain refiner that can
reduce grain size of hypoeutectic Al–Si casting alloys. However, its grain
refinement performance remains to be improved. In this work, the grain
refinement efficacy of Al–Nb–B master alloy is significantly enhanced by
modifying the Nb/B ratio through thermodynamic calculation. An Al–Nb–B
master alloy with optimum Nb/B ratio of *10:1 provides a fully equiaxed
structure across the sections of the Al–10Si and commercial Al–9Si–0.08Ti alloys
with an average grain size below 220 lm. The phenomenon is attributed to the
existence of NbAl
3
and the higher number density of NbB
2
at the Nb/B ratio of
*10:1, which offers sufficient active nucleating sites to promote the formation
of smaller grains. Moreover, the segregation behavior of Si atoms and interfacial
energies after doping Si are investigated by first-principles calculations, and the
results reveal that Si tends to segregate to the NbAl
3
/a-Al interface, whereas
grain refining potency of NbAl
3
for Al remains unchanged. This study has
implications for strategic design of Al–Si cast alloy with fine and equiaxed grain
structure inoculated by grain refiner.
Introduction
Hypoeutectic Al–Si cast alloys have been widely used
in automotive industry due to their low density,
excellent special strength, and adequate castability
[1,2]. Generally, a refined microstructure, which can
be commonly achieved with the addition of grain
refiners, is crucial for improving mechanical proper-
ties, reducing porosity and hot tearing, and modify-
ing secondary phase distribution [3].
The widely used Al–5Ti–1B master alloy [46]is
effective in refining wrought aluminum alloys, but
ineffective in refining the casting aluminum alloys
Address correspondence to E-mail: shuliqian@shu.edu.cn
https://doi.org/10.1007/s10853-019-03915-9
J Mater Sci (2019) 54:14561–14576
Metals & corrosion
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Recently, it was reported that NbB 2 particles could also serve as nucleation sites for Mg grains during solidification, resulting in grain refinement [15][16][17][18]. Nb-based heterogeneous nuclei were firstly used to refine Si-containing aluminum alloys to avoid the "poisoning" effect [19,20]. Bolzoni et al. investigated the grain refinement effect of Nb-containing particles on Mg-Al alloy. ...
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