Abstract
In order to investigate the competitive interaction between nanoparticles and twin, the eutectic Si microstructures in Al–10Si (wt. %) base alloys with exclusive and combined addition of Sr and Sb are characterized by combined TEM and atom probe tomography (APT). The chemical short range order in Sb–Sb and Sb–Sr pairs is revealed by ab initio molecular dynamics simulation, which promotes the formation of clusters and nanoparticles. The coexistence of nanoparticles and twins is observed in Sb containing alloys, with a negative correlation in the corresponding number density, owing to the competitive stacking of precursors and individual atoms at the solid–liquid interface. Large size particles around 70 nm with a uniform distribution of Sr atoms are formed in Al–10Si–0.35Sb–0.015Sr (wt. %) alloys, due to the precursor aggregation and homogeneous nucleation in the droplets that nucleation are depressed. A model for the formation of nanoparticles and their interaction with twins is proposed.
Highlights
Al–Si alloys have been widely used in machinery, automobiles, and aircraft, due to high specific strength, liquidity, and price ratio
Understanding and controlling the growth process of eutectic silicon is the key to improve the performance of Al–Si alloys, of which a prerequisite is to elucidate the evolution of microstructures and their interactions, such as twinning, stacking faults, and nanoparticles
The characteristic temperatures in the solidification curves indicate the nucleation of eutectic Si is slightly depressed with an undercooling of 0.1 °C,◦ as well as indicate the nucleation of eutectic Si is slightly depressed with an undercooling of 0.1 C, as well that in the Al–10Si–0.35Sb alloy
Summary
Al–Si alloys have been widely used in machinery, automobiles, and aircraft, due to high specific strength, liquidity, and price ratio. With the progress of technology, studies on microstructure evolution to further improve mechanical performance have drawn more and more attention, such as decreasing the secondary dendrite arm spacing [1], eliminating solidification defects [2], and modification [3,4,5,6,7]. Understanding and controlling the growth process of eutectic silicon is the key to improve the performance of Al–Si alloys, of which a prerequisite is to elucidate the evolution of microstructures and their interactions, such as twinning, stacking faults, and nanoparticles. As is well-known, the interaction between twins and precipitates is essential for the in-depth understanding of the formation and evolution of twins during solidification, but it is important for the strength increase during deformation [8,9]. The interaction of Materials 2018, 11, 1404; doi:10.3390/ma11081404 www.mdpi.com/journal/materials
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