Tuesday, 3 October 2017: 08:40
Camellia 2 (Gaylord National Resort and Convention Center)
The atmospheric aluminium alloy pitting corrosion behaviour shown in the literature and here indicted that the maximum pit sizes measured versus duration did not fit either cathodic or anodic limited growth kinetics. To further elucidate the pit growth mechanisms environmental data was analysed using statistical simulations, and a series of pseudo atmospheric exposure tests were performed. The statistical analysis pointed towards a “packet” mechanism of atmospheric pitting corrosion. In other words packets or populations of corrosion pits are created when aluminium surfaces are atmospherically wet. The individual pit growth is initiated when surface wetness occurs, the pits propagate whilst the surface remains wet and terminate when the surface dries. These pits do not then grow during subsequent wetness, and “packets” of pits are created during each wetness period. This mechanism was verified by the laboratory testing that demonstrated that rapid pit growth during the relative humidity (RH) induced wetness periods could account for the long term atmospheric pitting observations. The growth kinetics of pits under droplets was shown to be under cathodic limitation that was approximately equivalent to the oxygen reduction kinetics on the aluminium surface.