Pitting corrosion is considered tp be one of the'principal degradation mechanisms for high-strength aluminum alloys, and has been extensively studied [1-9]. Because pitting involved localized sub-surface attack, there has always been considerable interest in the process of pit development and its size and shape as they relate to the understanding of mechanisms and the characterization of kinetics of pit growth. Surface observations and serial sectioning tcehiques are most often used in the study of pitting. These techniques provide essentially two-dimensional information and can be tedious to apply. Furthermore, the information is limited (or inadequate) and can be misleading. For example, the appearance (top view) of surface damage represents only external manifestation of pitting, and provide no information on the depth or breadth ofsuch damage. Often the size of a relatively small opening remains unchanged while extensive pitting takes place beneath the surfnce. Serial sectioning, on the other hand, can provide useful inforrnation, but requires direful polishing and reconstruction; It is most effective for isolated large pits of hundreds of micrometers, and is impractical for smaller pits or clusters of pits because of imprecision in pit location and polishing control.
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