Modeling localized corrosion with an effective medium approximation

A model of localized corrosion is developed, in which the effective local properties of the electrolyte are adjusted based on a continuously variable porosity parameter that permits penetration of the electrolyte into the corroding medium in an average sense. The model is applied to corrosion of multilayer aluminum alloy electrodeposits in salt water, and compared to experimental results on several different coatings. The model can accurately reproduce a number of phenomena specific to localized corrosion, including the effects of variations in film thickness, dissolution through a barrier, and relative lifetimes of different coatings in immersion conditions.