Galvanic Corrosion and Anodic Dissolution of Fe and Fe-Al Alloys

Abstract

Fe-Al alloys of various compositions have been prepared by electron beam melting in a vacuum. The corrosion behavior of pure Fe and Fe-Al alloys has been investigated in a solution containing chloride ions. When pure Fe and an Fe-Al alloy make a galvanic couple in 5mass% NaCl solution, both the 33.61mass% Fe and 41.19mass% Fe-Al alloys acted as sacrificial anodes to protect the pure Fe. Conversely, the pure Fe suffered significant galvanic corrosion as a result of contact with the Fe-Al alloys such as 46.11mass%Fe-Al, 60.38mass% Fe-Al and 74.38mass% Fe-Al. The anodic dissolution of pure Fe proceeded by the hydroxide mechanism or the chloride mechanism in both the (xNaCl+yHCl) and (xHClO₄+yHCl) solutions (x+y=4.50kmolm^-3). On the other hand, the anodic dissolution of both the 33.61mass% Fe and 60.38mass% Fe-Al alloys could be interpreted by the chloride mechanism in the (xHClO₄+yHCl) solutions and low [OH^-]-(xNaCl+yHCl) solutions (logC_H⁺>0). In the high [OH^-]-(xNaCl+yHCl) solutions (logC_H⁺<-0.5), the inhibition effect of OH^- ions on the anodic dissolution was weak for the 33.61 mass% Fe-Al alloy, whereas a significant decrease was observed in the anodic dissolution current of the 60.38mass% Fe-Al alloy, which may be caused by passivation.