ABSTRACT
Contact of dissimilar metals in aqueous media is a frequent cause of premature corrosion yet, with appropriate foreknowledge, it can be controlled and with proper design and materials selection it should seldom be encountered. When two dissimilar metals in electrical contact are exposed to an aqueous medium, the less noble metal in general suffers more corrosion and the more noble metal suffers less than if they were isolated in the same medium. The increased attack on the less noble metal is called galvanic stimulation. The combination of metals producing the effect is a bimetallic couple. To aid selection, metals and alloys are assigned to the following compatibility groups: strongly electronegative metals, base metals, intermediate metals, noble metals, strongly passivating metals and cathodic collectors. The chapter also discusses that galvanic protection by coatings include zinc coatings on steel. Zinc coatings can be applied to steel sheets with the dual purpose of galvanic protection and providing a substrate for paint systems.
