Chromated aluminum alloy (AA)2024-T3 (UNS A92024) panels were exposed to neutral salt fog (NSS) over a range of salt fog fallout rates. Exposure was continued well beyond the standard testing periods (e.g., 168 h or 336 h) until there was general breakdown across the surface. From visual observation using the unaided eye, it was found that the development of pits on the surface went through four stages:
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induction: where no pitting occurred
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the development of a small number of pits
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substantial growth in pit numbers
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stabilization of pit numbers
The number of pits on the surface was strongly dependent on the salt fog fallout rate and, hence, total chloride dose. The time to failure (appearance of a limited number of pits) as defined under various standards was essentially independent of the salt fog fallout rate.
