Cathodic protection of aluminium in seawater

Abstract

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.