Abstract
The mechanical properties of Al-Si cast alloys are mainly controlled by the morphology of the eutectic silicon. Phase-field simulations were carried out to study the evolution of the multidimensional branched eutectic structures in 3D. Coupling to a Calphad database provided thermodynamic data for the multicomponent multiphase Al-Si-Sr-P system. A major challenge was to model the effect of the trace element Sr. Minor amounts of Sr are known to modify the silicon morphology from coarse flakes to fine coral-like fibers. However, the underlying mechanisms are still not fully understood. Two different in literature most discussed mechanisms were modelled: a) an effect of Sr on the growth kinetics of eutectic silicon and b) the formation of Al2Si2Sr on AlP particles, which consumes most potent nucleation sites and forces eutectic silicon to form with lower frequency and higher undercooling. The phase-field simulations only revealed a successful modification of the eutectic morphology when both effects acted in combination. Only in this case a clear depression of the eutectic temperature was observed. The required phase formation sequence L → fcc-(Al) → AlP → Al2Si2Sr → (Si) determines critical values for the Sr and P content.
Highlights
Hypoeutectic Al-sites for (Si) alloys offer excellent casting characteristics, good ductility and corrosion resistance
The mostwidely accepted theory is that adsorbed Sr atoms hinder the growth of (Si) in the preferred growth direction and trigger multidirectional twinning. [4, 5]. Another well-approved hypothesis is that Al2Si2Sr precipitates neutralize the fine dispersed AlP particles as nucleation sites for (Si), reducing its nucleation frequency [6, 7]. We considered both hypotheses in our phase-field model and performed 3D microstructure simulations to test which of both aspects dominates the modification of the eutectic structure
The temperature evolution with time was calculated from the balance of heat extraction and growth-related latent heat release averaged over the calculation domain
Summary
Hypoeutectic Al-Si alloys offer excellent casting characteristics, good ductility and corrosion resistance. A drawback is the coarse flaky morphology of the unmodified eutectic (Si) phase which deteriorates the mechanical properties and favors cracking [1]. [4, 5] Another well-approved hypothesis is that Al2Si2Sr precipitates neutralize the fine dispersed AlP particles as nucleation sites for (Si), reducing its nucleation frequency [6, 7]. We considered both hypotheses in our phase-field model and performed 3D microstructure simulations to test which of both aspects dominates the modification of the eutectic structure.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: IOP Conference Series: Materials Science and Engineering
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
