The most important corrosion type in these environments will be pitting. And alloys with good resistance against pitting corrosion can be used. The
5000-group alloys will have the lowest pitting corrosion rates, but alloys from
the 6000-series will perform satisfactorily in most applications. Copper
containing alloys are not recommended. In order to get sufficient life on immersed
structures it may be necessary to apply some kind of surface treatment like an epoxy or polyurethane lacquer or to use cathodic protection (CP). It is very appealing to use CP on aluminium, because of the low total
current demand. This is because only small parts of the surface are attacked,
i.e. the pits, while the rest of the surface is protected by the natural oxide
layer and needs no additional protection.
The high content of chlorides in sea-water environment makes it very important
to avoid entrapment areas, unfavourable bimetallic couples and other possible corrosion susceptible
areas.
Boats and other structures exposed to sea-water are often treated with
anti-foulants, some of these can contain copper and should not be used on aluminium.
Because the copper would act as a small cathode and increase corrosion on aluminium.
Corrosion in sea-water (Topic 11015)