An advanced mathematical approach to describe the influence of corrosion products on the corrosion rate is presented here. The related model can be used as input equation for numerical predictive corrosion simulations or simply as an empirical model, to extrapolate experimental data of corrosion tests to longer times and to interpret the physical parameters behind. This semiempirical model assumes that a constant share of the dissolved metal precipitates on the surface and hinders the diffusion processes. Hence, the effective corrosion rate decreases exponentially with increasing dissolution. The explicit corrosion progress over time is derived by time integration on a newly developed, time dependent corrosion rate equation. The derived expression can be effortlessly implemented in existing for example finite element method, which is demonstrated for the uniform corrosion of a zinc surface. Furthermore, this approach is qualitatively compared with other empirical models for corrosion products and the validity is demonstrated by fitting of experimental data. A very good agreement between experiment and theory can be achieved for various materials and environments considering no change of the driving corrosion mechanism.K E Y W O R D S corrosion products, corrosion simulation, finite element method, mixed potential theory, uniform corrosion

An advanced computational model based on the mixed potential theory (MPT) is presented, which is able to predict the progress of uniform as well as galvanic corrosion on car components made of zinc and steel (CR300). Previous approaches based on the MPT are computationally less challenging than other simulation models and are typically suitable for galvanic corrosion. In this work, an approach closer to reality is proposed by considering uniform corrosion aspects. Therefore, the metal surface is characterized by oxygen‐deficient and oxygen‐rich areas to model the anodic and cathodic reactions, respectively. Polarization curves are measured in 5 wt% NaCl electrolyte and are then used during finite element methods (FEM) simulation as respective boundary conditions on the metal surface, leading to a multiple microelectrode system. By randomly defining the microelectrodes as cathodes or anodes, that is, assigning polarization data from the oxygen‐rich or oxygen‐deficient electrolyte, the uniform corrosion is modeled. The independence of the corrosion rates from the arbitrary model parameters and surface width (up to 1 mm) is confirmed. The results from this FEM simulation for zinc and a low‐alloy steel are compared to the normed neutral salt spray (NSS) test and show good qualitative agreement. Further on, the galvanic corrosion of a zinc‐steel couple is modeled and the expected result for varying cathode‐anode surface ratio is reproduced.

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