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 inter-granular 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.