EVOLUTION OF THE CHEMISTRY OF PASSIVE FILMS OF SPUTTER-DEPOSITED, SUPERSATURATED AL-ALLOYS

The passivity and corrosion behavior of several supersaturated aluminum alloys formed by cosputter deposition have been investigated. Several of these alloys exhibit superior resistance to localized attack in electrochemical polarization measurements and salt fog tests. X-ray photoelectron spectroscopy was used to examine the surface chemistry of the passive film as a function of applied potential for Al, Al-Ta, and Al-Zr alloys. The passive film that forms on each alloy becomes enriched in oxidized solute as the specimen is anodically polarized. In general, the oxidized solute protects the substrate by restricting the ingress of chloride and oxygen and thereby preventing or reducing localized attack and film growth, respectively. Of the solutes examined, Ta is the most effective in this regard; the passive film on Al-Ta alloys remains thin and protective at the most noble potentials. Breakdown occurs only as the potential drop across the film becomes great enough to allow the transport of chlorides. © 1990, The Electrochemical Society, Inc. All rights reserved.