Corrosion of AA5083 marine grade aluminium

Brief Description

Marine grade AA5xxx series Al alloys including AA5083 have been widely used for the construction of commercial fast ferries, as well as for patrol boats operated by the RAN and Australian Customs Service. AA5083 has also been used in the superstructures of the Adelaide Class guided missile frigates and the former RAN Landing Platform Amphibious, as well as the hull of the Australian Army H113 armoured vehicles.

For RAN patrol boats, the hull exterior is painted and the interior surfaces are generally left bare, which is consistent with typical ship building practices for commercial vessels manufactured from marine grade Al alloys. However, whilst AA5083 has an industry reputation for good corrosion performance in commercial fast ferries, the corrosion performance of AA5083 on RAN vessels has been very disappointing, with wide-spread and frequently severe corrosion of AA5083 hull plate initiating at internal unpainted surfaces. This apparent severe disparity in corrosion performance of AA5083 between commercial vessels and RAN experience, without any clear explanation, demonstrates that the scientific understanding of the susceptibility and mechanisms of corrosion of AA5083 in marine environments is currently inadequate. This lack of scientific knowledge undermines confidence in the use of marine grade Al alloys for future RAN vessels.

Whilst there have been substantial research efforts overseas to examine intergranular stress corrosion cracking as a result of sensitisation of AA5xxx alloys, DSTO testing indicates that the poor corrosion performance of AA5083 on RAN vessels is not due to sensitisation. Consequently, further research is required on the susceptibility and mechanisms of corrosion of non-sensitised AA5083 in marine environments if Al alloys are to be used with confidence for future RAN vessels.

Scope of the work

A PhD program will investigate the susceptibility and mechanisms of corrosion of AA5xxx series alloys, specifically AA5083, under conditions representative of RAN service. Improved scientific understanding will lead to identification of potential improvements in detailed design, fabrication and maintenance practices for AA5xxx alloys to avoid or minimise corrosion in service.

Which SEA program would benefit and how? Final outcome and impact (eg TRL increase?)

SEA1179 Patrol Boat Replacement, SEA1180 Offshore Combatant Vessel, plus current ACPBs through improved maintenance practices.
Improved scientific understanding will enable ship designers, fabricators and maintainers to synergistically modify their practices in order to consistently achieve good corrosion performance of Al alloy hulled vessels in RAN and Australian Customs service.