PASSIVITY OF HIGH CORROSION-RESISTANT CU-AL-SN ALLOYS

In a work studying the corrosion and tarnishing properties of a variet y of copper alloys, the alloy Cu-Al10-Sn5 was found to show an excelle nt corrosion resistance in neural solutions, where copper and most con ventional Cu alloys are covered by thick nonprotective surface layers. The passive films formed on this alloy were characterized with electr ochemical and photoelectrochemical methods. The pH dependence of the p assivation and of the photocurrent behavior of the Cu-Al10-Sn5 alloy c learly indicates that the passivity of this alloy in neutral solutions is due to a formation of passive film enriched with aluminum oxide. A t corrosion potential a strong increase in the corrosion resistance wi th time is due to a gradual enrichment of the surface with aluminum ox ide. This can be seen in the photocurrent spectra which change from '' copper-type'' to ''aluminum-type'' with time. At higher applied potent ials the formation of an aluminum-type oxide film is strongly accelera ted.