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Pitting corrosion of aluminium alloy AA5005-H34 immersed in natural sea water for up to 2 years is presented, together with new interpretations of the development of the pitting process over extended exposure periods. Trenching initiated at surface-located Fe-rich intermetallic (IM) particles. It occurred more extensively in sea water compared to atmospheric exposures. With increasing exposures, the pitting morphologies became more complex. Three types, i.e. hemispherical pits (Type 1), crystallographic pits (Type 2) and characteristic 'petal'-like pits (Type 3), were observed after 12 months. It is suggested that the formation of Type 2 and Type 3 pits occurs at an advanced corrosion stage, and are associated with large Fe-rich IM particles near the metal surface. The influence of marine growth on pitting was negligible.

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