Galvanic corrosion is electrochemical corrosion resulting from the formation of a cell by contact between two different conducting materials in an environment providing an electrolytic medium.
Under these conditions a galvanic couple is formed.
The two materials must be electrical conductors. In composite materials galvanic corrosion can only take place in the presence of conducting fibres (essentially carbon, but boron is also possible).
The two materials must be different and in electrical contact. Galvanic corrosion will mainly appear in the areas where a metallic structure has been assembled with a carbon/resin composite structure, and in the zones where two carbon/resin composite structures are joined using metal elements (e.g. screws, rivets etc.).
The electric circuit must be closed, which will be the case in an electrolytic medium (i.e. an electrolyte). A marine environment (humidity + sodium chloride) is ideal for galvanic corrosion.
The two materials must have different dissolution potentials, which is exactly the case for carbon with aluminium.