Complex Pitting Corrosion in Long-Term Immersed Exposures of 6060 Aluminum Alloys in Temperate Natural Seawater

Novel observations of changes in pitting morphology of 6060 aluminum alloys immersed for periods of 3 y, 3.5 y, and 4 y in temperate seawater are reported. They indicate that the initiation and propagation of pitting involve several different mechanisms. These result in small (semi-) hemispherical pits, irregular polygonal-shaped larger pits, and also extremely large and deep pits with complex morphologies. Principally intergranular corrosion and crystallographic pitting were observed. It is proposed that the changing nature of the pit morphologies is associated with the accumulated corrosion products and, to a lesser extent, affected by the marine growth attached to the metal surface.