Quantitative simulation of Fe-rich intermetallics in Al-Si-Cu-Fe alloys during solidification

Fe-rich intermetallic phases (e.g. β-Al5FeSi) which form during the solidification of Al-Si-Cu-Fe alloys can have a detrimental effect on the mechanical properties of cast components. A thermodynamic database was combined with a numerical solution of the multicomponent diffusion solver to predict the formation of this phase. The growth kinetics and morphology was simulated using a combined Monte-Carlo algorithm to calculate the transformation frequency for each cell as a function of total free energy, with the faceted shapes replicated via a decentred needle/plate algorithm. The non-stoichiometric composition of both Fe and Si was simulated by changing the partition coefficient at the S/L interface according to local kinetic parameters such as growth velocity and effective diffusion. The model predicted phase fraction, size and morphology of Fe-rich intermetallic phases in type-319 alloys (Al-7.5wt.%Si-3.5wt.%Cu-0.2 ∼ 0.8wt.%Fe) compared well to high resolution synchrotron tomography results.