Aluminium Design and Construction John Dwight

The severity of bimetallic corrosion of aluminium generally depends
on the second metal’s position in the series, although there are exceptions.
In contact with steel, a common juxtaposition, aluminium will suffer
serious corrosion, especially if the surface area of the steel is comparable
to that of the aluminium; likewise with cast iron. Suitable precautions
are essential (Section 3.7.5). With copper and copper-based metals (brass,
bronze), the attack is more severe, and preventative measures are even
more vital. The serious effect that copper can have on aluminium is
illustrated by the case of a cycle shed once installed at Cambridge
University, on which the aluminium sheeting was perforated in a few
months by drips of rainwater from a copper roof five storeys above.
With lead, surprisingly, the effect is much less pronounced and
preventative measures are only needed in severely polluted environments
(industrial or marine). Austenitic stainless steels can safely be used with
aluminium, generally without any precautions. With zinc, which lies below
aluminium in the table, the zinc rather than the aluminium gets attacked,
as with galvanized coatings. The same applies with magnesium.
Bimetallic corrosion of aluminium can sometimes be put to good use
in providing cathodic protection. Thus, in the North Sea, it is common
practice to fix long aluminium bars (anodes) to the steel tubulars of
jacket structures in the splash zone. The rate of rusting on the steel is
thereby reduced, at the expense of the sacrificial aluminium anodes.
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