Cathodic protection of aluminium in seawater

Cathodic protection of various 6000 aluminium alloys and variants of EN AW-5083 in seawater has been studied. The alloys were immersed in seawater and polarized to about -1.06 V versus Ag/AgCl for 1 year. The cathodic current density increased initially due to formation of a copper film on the surface, but the effect was temporary. After 200 days, the current demand for cathodic protection had stabilized on all the investigated alloys at 0 to about 20 mA/m2, depending on the Fe/Si ratio in the alloy. Depending on the content of noble intermetallic particles, the aluminium will corrode at a low and constant rate. Application of a coating on the aluminium will decrease the cathodic current demand for cathodic protection significantly. Coatings on submerged aluminium are very stable and not susceptible to degradation mechanisms like cathodic disbonding. The cathodic current density for cathodic protection of aluminium depends on the alloy composition. An initial high current correlated with Cu content in the alloy, while after 1 year the current density was much lower and determined by the Fe/Si ratio of the alloy. image