Confocal laser scanning microscopy was used in an in situ fluorescence mode to investigate localized corrosion of aluminum alloys in the presence of 0.1 M KCl. Fluorescein dye was used to indicate pH changes and surface chemistry over and around the active sites. Al 6061 was found to have at least two kinds of inclusions according to their elemental constituents. Active inclusions that are rich in Mg, Si, and Al show fluorescence activity in early stages of exposure. The inclusions that are rich in Fe, Si, and Cr show no fluorescence activity at the early stages. Al 2024 was also studied and had different fluorescent activities that were associated with different inclusions.