Several analytical models have been developed through the years to describe the formation and growth of the internal oxidation layer in binary alloys. Such models are often complex and their validity strongly rely on precise measurements of molar fluxes of the different species involved in the oxidation process. The main disadvantage of such measurements is that they are difficult to made and present a high degree of uncertainties, thus some assumptions are needed to ease understanding and the applicability of them. In this paper we set up a numerical scheme (finite differences) to describe the growth of the internal oxidation layer in binary Cu-Al alloys oxidized in air at different temperatures. There is good agreement between the experimental results and the values calculated with the aid of our numerical approach.