Passivity of High Corrosion Resistant Cu‐Al‐Sn Alloys

Abstract

In a work studying the corrosion and tarnishing properties of a variety of copper alloys, the alloy Cu‐Al10‐Sn5 was found to show an excellent corrosion resistance in neutral solutions, where copper and most conventional Cu alloys are covered by thick nonprotective surface layers. The passive films formed on this alloy were characterized with electrochemical and photoelectrochemical methods. The pH dependence of the passivation and of the photocurrent behavior of the Cu‐Al10‐Sn5 alloy clearly indicates that the passivity of this alloy in neutral solutions is due to a formation of passive film enriched with aluminum oxide. At corrosion potential a strong increase in the corrosion resistance with time is due to a gradual enrichment of the surface with aluminum oxide. This can be seen in the photocurrent spectra which change from “copper‐type” to “aluminum‐type” with time. At higher applied potentials the formation of an aluminum‐type oxide film is strongly accelerated.