Pit growth kinetics in aluminum: effects of salt loading and relative humidity

Abstract

The growth kinetics of localized corrosion, e.g. pits, in corrosive environments often controls the service life of metallic components. Yet, our understanding of these kinetics is largely based on coupon-level, e.g. mass-loss, studies which provide limited insights into the evolution of individual damage events. It is critical to relate observed cumulative loss trends, such as links between changing humidity and mass loss rates, to the growth kinetics of individual pits. Towards this goal, we leverage in-situ X-ray computed tomography to measure the growth rates of over sixty pits in aluminum in four different humid, chloride environments over ≈3 days of exposure. Pit growth rates and final volumes increased with increasing droplet volume, which was observed to increase with increasing humidity and salt loading. Two factors, droplet spreading and oxide jacking, dramatically increased pit growth rates and final volumes.