AES STUDY OF SURFACES PRODUCED BY SELECTIVE DISSOLUTION IN Al-Cu ALLOYS.

The evolution of surface structure in sulfuric acid was examined in depth profiles for alloys from 0. 06% to 2. 0% Cu and the results interpreted with the aid of concurrent TEM and electrochemical observations. At minus 500 mV(SCE), an immune potential for copper, a dispersion of small copper particles on the substrate and an underfilm enrichment were present. At minus 100 mV(SCE), there was a significant dissolution current for copper; underfilm enrichment was still present but evidence of particles only in the 2. 0% Cu alloy. The basic enrichment step was taken to be the formation of a pure alumina film over the alloy, and a copper signal from within the film in one alloy is attributed to trapped copper fragments not visible by TEM. Mechanisms of copper loss from the electrode are discussed.