Five-year corrosion of aluminium alloys at several marine sites

Abstract

Eight aluminium alloyswereexposedat marine sites at Kure Beach, North Carolina; Arenzano, Italy; and Bohus-Malmon, Sweden. Panels were removed at the end of 1-, 2- and 5-year exposure periods and evaluated for depth of pitting, corrosion rate and loss of mechanical properties. The high-purity aluminium and certain aluminium–magnesium alloys showed the lowest corrosion rates based on weight losses. The site at Arenzano generally was most severe as regards depth of pitting and weight loss with the Kure Beach, North Carolina, 80-foot lot being next in severity. Both pit-depth growth and corrosion rate decreased with exposure time for all alloys and locations. Several alloys, at the more severe sites, showed some decreases in some mechanical properties as measured by elongation of tensile specimens, but these changes are not of such magnitude as to be structurally significant.

Aluminium–magnesium alloys 5050, 5052, 5086 and 5154 are among the best for use in marine environments. The structural alloy 6061 is also highly satisfactory for marine atmospheres. A maximum pit depth for all alloys of about 15 mils was found after five years at Arenzano and about 9·5 mils for the same period at Kure Beach 80-foot lot.