The effect of aluminium allying on the corrosion resistance of cast steel

There is some evidence that the addition of small amount of aluminium can reduce the atmospheric corrosion of steel. However, systematic long-term investigations are lacking. There also appears to be no information about resistance of such alloys to marine immersion conditions. This paper reports on the marine environment corrosion performance of steel alloyed with aluminium additions of 0% (control), 2%, 4%, 6% and 8%. The cast steel was forged into billets and machined into coupons. Sets of coupons were exposed to three exposure conditions: (a) in temperate seawater for 1, 2 and 3 years, (b) submerged below the mud-line for 1, 2 and 3 years and (c) exposed at two extremely severe atmospheric marine locations for 12 months. The results show that the increase in Al content reduced corrosion loss in submerged conditions from 10.5% after one year to 2.8% after 3 years. In the coastal atmosphere, corrosion loss dropped from 5.5% after one year with no Al addition to 1.2% with 8% Al alloying. The corrosion resistance in marine mud buried conditions was less favourable. Corrosion loss reduced from 4.4% after one year to 2.9% after 2 years but in some instance the addition of Al had minimal or no effect on corrosion resistance. These observations add to the body of knowledge regarding the effect of aluminium on long-term corrosion loss.