Stability, chemical composition, and structural and electronic properties of the intermetallic compound τ4-(Al1-xSix)5Fe

τ 4 -(Al 1-x Si x ) 5 Fe particles form during casting of Al-based alloys. They have strong impacts on the solidification process and the mechanical performance of the products. Meanwhile, experiments revealed notable variations in lattice parameters and chemical compositions for the manufactured Al alloys, and knowledge about the intrinsic properties of the τ 4 -phase is still far from complete. We here investigate the crystal chemistry and electronic properties of the τ 4 -phase using a combination of ab initio modelling and thermodynamics analysis. The study justified the τ 4 -Al 3 Si 2 Fe superstructure at low temperature. There is a shallow potential valley in the formation energy vs Si content curve, corresponding to its compositional and structural flexibility. Thermodynamics analysis revealed kinetic effects on its chemical composition and Al/Si distribution during casting. The obtained information helps understand the formation of and characterize the Fe-IMCs particles in Al alloys, and design novel Al alloys and manufacturing processes for recycling Al. • First-principles calculations justified the τ 4 -Al 3 Si 2 Fe superstructure model at low temperature. • Thermodynamics analysis revealed configurational entropy stabilized the configurations with a broad range of Si contents in the crystals during casting. • There is a balance between the Si stabilization effects and Si-Si repulsive interactions. • The complex relations between the lattice parameters and Si content in the crystals were revealed. • The obtained information helps understand the formation of and characterize the Fe-IMCs particles in Al alloys, and design novel Al alloys and manufacturing processes for recycling Al.