Pitting Corrosion of 5005 Aluminium Alloys in The Temperate Seawater Immersion Environment

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Pitting is the most commonly occurring corrosion form for aluminium alloys. In natural seawater environments, pitting progress can be complex and may be affected by factors that cannot be replicated by accelerated corrosion tests using a simulated seawater as the corrosion media in the laboratory. This paper reports pitting behaviour of 5005 series aluminium alloy sheets exposed to natural temperate seawater at Taylors Beach on east coast of Australia. The corrosion morphologies were observed by Scanning Electron Microscopy and the compositions of different parts of the metal as well as the corrosion products were analysed by Energy Dispersive Spectroscopy. Pitting was observed to initiate at the sites where intermetallic particles are present. Hemispherical pits form as a result of trenching at the periphery of Fe-containing intermetallic particles. After 6 months, characteristic ‘petal’-like morphology was repeatedly observed. Crystallographic pitting was observed on coupons exposed for 12 months and 24 months. These are the dominant pitting morphologies and this possibly indicates a change of mechanism for the pitting process.

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