A model for solving isothermal solid-solid phase transformations in multicomponent aluminium alloys is presented. A multiphase-field model for the dissolutions of various phases in an aluminium matrix during homogenization is presented. Driving forces for phase transformations are calculated using data obtained from the commercial software JMatPro and an aluminium database. An integrated concept of the multiphase-field model with solute diffusion is used. A one-dimensional model for the simultaneous dissolution of the Mg(2)Si and Si phases in the aluminium matrix of ternary Al-Mg-Si alloys is introduced. An explicit central finite difference numerical scheme is used for the solution of the time transient phase-field equations and the solute diffusion equations.