Real-time observation of localized pH changes during corrosion of aluminum alloy 2024-T3

Changes in solution pH during corrosion of aluminum alloy 2024-T3 in dilute, aqueous, near-neutral chloride environments were investigated using in-situ fluorescence microscopy. Although localized corrosion occurred at the majority of s-phase particles, pH changes were only observed at a minority of sites. Transient solution acidity, consistent with particle de-alloying, was observed above a minority of isolated s-phase particles. Transient solution alkalinity was observed to be associated with a minority of particles or with isolated regions on the sample surface. The observation of transient alkalinity at one site was often correlated with a high rate of pitting at a remote site, as evidenced by localized solution acidity and hydrogen evolution. These results suggest that, for the experimental conditions explored here, solution alkalinity develops in response to localized, accelerated attack at remote sites.