Effects of Dissimilar Metal Coupling, Potential Distribution, and Temper Condition on Galvanic Corrosion of 5086 Aluminum Alloy in Synthetic Seawater

Abstract

The galvanic corrosion behavior of 5086 aluminum alloy in three tempers {Hll6, Hll7, H32) when coupled with more noble metals {1040 steel, naval brass, and Ti-150A titanium) and immersed in aerated synthetic seawater, was studied. Galvanic current density measurements, potentiodynamic polarization determinations, and optical and electron microscopic observations were made. Galvanic corrosion of 5086 aluminum was found to be independent of temper and to decrease in the order (of coupled metals) Ti > naval brass> 1040 steel. The effect of dissimilar metal coupling decreases with time due to the formation of corrosion or product deposits on both anodic and cathodic surfaces. Coverage of the surface of the aluminum (anodic) member of couples with corrosion products tends to promote the operation of local corrosion modes. Correlations have been made between corrosion product distribution and the distribution of dissolution attack by microscopic means, and the relation of these features to potential distribution is discussed.