Three-component Al-Fe-Si systems with an equiatomic composition are high-strength alloys that are poorly resistant to plastic deformation. To increase the material ductility, a phase diagram of the Al-Fe-Si ternary system was constructed using ThermoCalc software. The conditions for the formation of the AL8FE2SI phase, which is an α-phase and has a hexagonal lattice, have been identified. At solidus temperatures, α-AL8FE2SI and β-AL9FE2SI2 are competitive. The conditions for the developing a single-phase region consisting of 97% α-AL8FE2SI have been identified. α-AL8FE2SI is a high-temperature phase; the system will perceive plastic deformation in the temperature range of 675–612 °C, with further phase conversion upon cooling.