1993 Volume 42 Issue 9 Pages 569-575
Effect of Cl- and dissolved oxygen on galvanic corrosion of 5182 aluminum alloy coupled with steel can stocks were investigated in 0.2% citric acid solutions containing various amounts of Cl- by electrochemical polarization and galvanic current measurements. In all solutions, 5182 alloy was anodic as expected from the fact that the alloy is less noble than the steel. It was found that galvanic current density is strongly dependent on the amount of dissolved oxygen and on the area in steel can stocks where coating is locally damaged and iron is exposed. In the solution containing 100ppm of Cl-, galvanic current density was of the order of a few μA/cm2, but it could be higher than 100μA/cm2 in the solution containing 5000ppm of Cl-. In the case where 5182 aluminum is coupled with 3004 alloy used for all aluminum can body stocks, on the other hand, galvanic current density was less than 5μA/cm2 even in the solution containing 5000ppm of Cl-. These results indicate that aluminum-steel bi-metal cans are not suitable for beverages containing higher concentrations of Cl-, because of latent problem of galvanic attack and also of higher self-corrosion rates of steel cans. Even for beverages containing lower concentrations of Cl-, there still arises a potential problem of galvanic corrosion if the inside coatings of steel can stocks are locally damaged and iron is locally exposed. Thus, it is considered that all aluminum cans are more preferable to steel cans for the cases where beverages are expected to contain higher concentrations of Cl-.
