Abstract
An improved finite element model was established to demonstrate the steric hindrance effect of the precipitated corrosion product (Al(OH)3) on micro-galvanic corrosion triggered by intermetallic particles (IMPs) in an Al-matrix. In this model, the precipitation/ dissolution of the corrosion product could occur in the whole liquid field as the result of a reversible reaction. Simulation results show that the precipitated insulating Al(OH)3 on the electrode surface can inhibit further corrosion by reducing the conductivity of the solution and the active electrode surface area. Meanwhile, the steric hindrance effect of the precipitated Al(OH)3 also slows down the diffusion and migration of species in the solution. Moreover, considering the porous nature of precipitated Al(OH)3, a porosity parameter ε was introduced to describe the degree of compactness of corrosion product, which reaches a certain minimum value εc under a specific corrosion situation. Compared to the previous work in which a surface coverage parameter was used to describe the blocking effect of Al(OH)3 on surface activity, the present model is more realistic in mimicking the micro-galvanic corrosion, and also useful for the simulation of the transition from metastable pit formation to pit propagation.
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