Modeling the uniform corrosion behavior of zinc in salt spray testing

Abstract Salt-spray testing is widely used in the automotive and materials industries to assess the corrosion resistance of protective coatings, where uniform corrosion is a key indicator of material performance. This work presents a numerical uniform corrosion model that predicts the corrosion rate of hot-dip zinc in salt-spray environments by incorporating electrochemical reactions, mass transport via the Nernst–Planck equation, and ionic-strength effects through the Brønsted–Bjerrum relation. The model is calibrated using immersion-test data and extended to account for electrolyte layer growth, droplet deposition, and periodic run-off in salt-spray environments. The calibration establishes a relationship between the porosity of the zinc oxide layer and the rate constant of zinc oxide precipitation. The validated model reproduces the transition from activation- to diffusion-controlled corrosion and captures the experimentally observed corrosion kinetics with an error margin of 20% when electrolyte renewal is included. The results highlight the decisive role of electrolyte dynamics in salt-spray environments and provide a foundation for extending the framework to more complex cyclic corrosion tests.