Pit Morphology, Dissolution Kinetics, and Gas Generation Monitored in Real Time during Localized Anodic Aluminum Corrosion

Localized corrosion in metallic materials is a stochastic phenomenon that causes irreversible structural failure. Its initiation, which occurs at the solid-liquid interface on the nanometer scale, remains difficult to predict and challenging to characterize. Herein, we describe an experimental platform that exploits advances in electrochemical liquid-phase scanning and transmission electron microscopy (LPSEM and LPTEM) to study pitting corrosion of thin-film pure aluminum in a saline environment in real time. Galvanostatic measurements at increasing current levels showed that localized corrosion of Al begins with the appearance of blisters in parallel with nanosized pits. It progresses with the coexistence of round and fractal-like pit morphologies before transitioning to the complete fractal-like dissolution of Al at high currents. Although gas bubble formation appeared to be more pronounced at higher currents, we were able to locally probe that the gas is produced at the corrosion front, which we experimentally confirmed to be molecular hydrogen. Our findings reveal the kinetic mechanism of the early stages of localized anodic corrosion in Al, which may have more general implications for proposing corrosion resistance descriptors.