Abstract:Expressing the partial molar excess Gibbs energy of component Al in Al-Si-Fe ternary alloy as a polynomial, then the coefficients A jk involved in the polynomial were determined based on the experimental date in ternary system and three selected binary subsystems through a least-squares technique. The coefficients F jk contained in the polynomial of excess molar free energy of alloy were drawn in the light of Gibbs-Duhem equation. The partial molar excss Gibbs energy for the components Si and Fe can be calculated by use of the coefficients A jk and F jk through a modified "I-D" approach. In present analytical model, the iso-activity lines of three component in the Al-Si-Fe ternary alloy were calculated in the whole homogeneous region.