ANALYSIS OF LOCAL CHANGES IN pH DURING DISSOLUTION OF ALUMINUM ALLOY 2024-T3 IN AQUEOUS NaCl

摘要

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 and digital image processing techniques. Image processing permitted identification of alkaline and acidic areas in the electrolyte during the evolution of the corrosion process. Observed pH behavior was in some cases consistent with predicted phenomena and in other instances contrary to descriptions found in the current literature. Although localized corrosion occurred at the majority of s-phase particles, transient solution acidity, consistent with particle de-alloying, was observed above only a minority of isolated s-phase particles. Uniform alkalinity over large areas of the sample, consistent with a microelectrode effect, was seen several times during the experiment but patterns of transient local alkalinity were more prevalent. Persistent solution acidity consistent with pitting was also observed.