A novel process named Controlled Diffusion Solidification (CDS) has been developed to circumvent problems that are typically associated with casting wrought aluminum alloy compositions into near net shaped components. The process involves bringing two precursor alloys of precisely controlled composition, temperature, and quantity into intimate contact, and then casting the resultant alloy using a conventional casting process to yield a component of predetermined composition with a microstructure that is similar to that of semi-solid processed alloys. Describing the many interactions that occur during solidification of aluminum alloys in a consistent manner is virtually impossible without the use of computational tools that are based on thermodynamic models. In this paper, we describe how the CALPHAD method, which allows calculating all the necessary data from thermodynamic model parameters, was used along with theoretical calculations and empirical rules to allow describing the Gibbs free energy of each phase in the alloy system and yield quantitative data that guided the development and optimization of the CDS method.