Moving boundary simulation and mechanistic studies of the electrochemical corrosion protection by a damaged zinc coating

[Display omitted] •Moving boundary simulation takes into account zinc electrode consumption by time.•Oxygen concentration variation in the scratch region plays a critical role in protection mechanism.•Sacrificial protection in the middle and barrier protection at the corners of the scratch.•Sacrificial protection period was predicted, and galvanic corrosion rate was quantified.•Current density is a better criterion than potential for sacrificial protection systems with a large Zn to Fe area ratio. The mechanism of corrosion protection of steel substrate by a 96 wt% zinc primer that was damaged by scratch was simulated. The primer was approximated to pure zinc layer due to high percentage of zinc. Results show that while the middle of scratch is protected by sacrificial protection, at the corners of scratch a local cathodic inhibition results in barrier protection due to variations in the dissolved oxygen concentration. Moving boundary simulation allowed to predict the changes to the geometry of the corroding electrodes. Finally, taking into account zinc electrodes consumption, the period of sacrificial protection was predicted by simulations.