Atmospheric and immersion corrosion of steel alloyed with aluminium

This paper reports a systematic study of longer-term marine atmospheric and immersion corrosion losses for mild steel alloyed with small to moderate amounts (0, 2, 4, 6 and 8% by weight) of aluminium. Such steel coupons were exposed for up to 3 years in temperate sea water and also just below the mud-line, and for up to one year at two severe atmospheric marine locations. Compared with the coupons without aluminium, higher aluminium content reduced corrosion loss in immersed conditions from 10.5% after one year to 2.8% after 3 years. Below the mud-line corrosion losses showed a similar trend but were more varied. In the marine atmosphere, the reduction in corrosion loss for increased aluminium content ranged from 58 to 81% after one-year exposure. The results show that aluminium alloying above about 4% has limited additional benefit for corrosion in any of the marine exposure environments.