Anodic oxidation of Al–Ag alloys

The anodic oxidation of solution-treated and quenched Al–Ag alloys containing 0.3, 0.6, 0.9 and 1.2 at.%Ag, is examined in ammonium pentaborate electrolyte, which leads to growth of barrier-type anodic films. Enrichments of silver, 3.1×10¹⁵ Ag atoms cm⁻², are developed in the alloys immediately beneath the amorphous alumina films, with the level of enrichment not depending significantly upon the composition of the bulk alloy. The enrichment is relatively low due to clustering of silver atoms in the bulk alloy, which reduces the concentration of silver that is available to enrich from solid solution. Silver species are incorporated into the anodic film, where they migrate outward faster than Al³⁺ ions.