Porous anodic film formation on an Al-3.5 wt % Cu alloy

Anodic film growth has been undertaken on an electropolished Al-3.5 wt % Cu alloy to determine the influence of copper in solid solution on the anodiz ing behavior. At the commencement of anodizing of the electropolished alloy , in the presence of interfacial enrichment of copper, Al3+ and Cu2+ ions e gress and O2- ion ingress proceed; film growth occurs at the alloy/film int erface though O2- ion ingress, with outwardly mobile Al3+ and Cu2+ ions eje cted at the film/electrolyte interface, and field-assisted dissolution proc eeding at the bases of pores. Oxidation of copper, in the presence of the e nriched layer, is also associated with O-2 gas generation, leading to devel opment of oxygen-filled voids. As a result of significant pressures in the voids, film rupture proceeds, with electrolyte access to the alloy, dissolu tion of the enriched interfacial layer and re-anodizing. The consequence of such processes is the development of anodic films of increased porosity an d reduced efficiency of film formation compared with anodizing of superpure aluminum under similar conditions. (C) 2000 The Electrochemical Society. S 0013-4651(99)03-090-6. All rights reserved: