The Effect s of Chloride Ions on the Corrosion of Aluminium Alloys used in the Construction of Australia II

During a routine condition report and corrosion assessment of the hull of the historic 12-metre yacht, Australia II, a bubbling liquid was found in the bilges. Rapid corrosion of structural aluminium alloys was occurring as a result of the accumulation of salty water under the floorboards. The offending liquid was removed and analysed before the surface was stabilised by a combination of desalination and the application of corrosion inhibitors. The most effective method involved the use of sodium metasilicate, acidified with phosphoric acid, since it inhibited corrosion whilst allowing removal of the highly aggressive chloride ions from the surface oxide layers. Subsequent commercial refurbishment, transport and corrosion have served to highlight the sensitivity of objects made of modern materials, designed for performance mode and not for longevity.