Transformation Mechanism of Fe-Containing Phases in Recycled Aluminum Alloys by First-Principles Calculations

A high level of Fe impurity restricts the sustainable recycling and wide application of recycled aluminum alloys. Optimizing the phase selection to favor less harmful Fe-containing intermetallics is a critical strategy to develop high-performance alloys with high Fe-level contamination. To reveal the intrinsic mechanism of Fe-containing intermetallic transformation in Al-Si-Fe alloys, the thermodynamic stability, thermal properties, elastic properties, and electronic structure evolution of θ-Al13Fe4, α-Al7.1Fe2Si, β-Al9Fe2Si2, and δ-Al3FeSi2 phases were systematically investigated by first-principles calculations. The calculated formation energy and binding energy of θ-Al13Fe4, α-Al7.1Fe2Si, β-Al9Fe2Si2 and δ-Al3FeSi2 are −0.28 eV/atom, −0.41 eV/atom, −0.57 eV/atom, −1.92 eV/atom and −4.95 eV/atom, −5.14 eV/atom, −5.35 eV/atom and −6.7 eV/atom, respectively. These results revealed that the thermodynamic stability shows an increasing tendency in the sequence of θ-Al13Fe4, α-Al7.1Fe2Si, β-Al9Fe2Si2 and δ-Al3FeSi2. The calculated Gibbs free energy, enthalpy, entropy, heat capacity, thermal expansion-temperature, and bulk modulus results demonstrated the increased stability in the sequence of θ-Al13Fe4, α-Al7.1Fe2Si, β-Al9Fe2Si2 and δ-Al3FeSi2 phases. These calculated thermal properties validated the phase transformation behaviors. Finally, the enhanced stability and increased modulus values of the δ-Al3FeSi2 phase is attributed to the stronger Si-Fe covalent chemical bonding caused by electron transfer. These findings provide new insight for designing recycled aluminum alloys by optimizing Fe-IMC phase selection and transformation pathways.