Initiation and propagation of atmospheric corrosion on aluminum alloys under a cyclic wet-dry condition with a constant dew point

To clarify the mechanism of the atmospheric corrosion of aluminum alloys in practical environments, a cyclic wet-dry corrosion test, in which the dew point of the circulating air was maintained at a constant level, has been conducted. The atmospheric corrosion of AA1100-O and AA6061-T6 aluminum alloys was randomly initiated around dispersed intermetallics due to the galvanic coupling between the aluminum matrix and intermetallics. The corrosion rate of aluminum alloys in the first cycle was higher than in the subsequent cycles due to the initiation of localized corrosion. As the number of wet-dry cycles increased, the increase of the amount of corrosion loss on aluminum alloys gradually tapered off, which was mainly attributed to the propagation of localized corrosion initiated in the first cycle. In the wet-dry conditions employed in our test, once localized corrosion was initiated in the first wetting period, no new sites of corrosion occurred in the subsequent cycles.