Electrochemical Etching of Copper Ion Implanted H-19 Aluminum in Aqueous Chloride/Sulfate Solution at 95 C

Electrochemical etching experiments were conducted with Cu ion implanted H-19 Al foil in aqueous NaCl/Na₂SO₄ solution at 95 C in an effort to improve the procedure for the surface area enhancement of Al. The concentration of Cu in unimplanted and implanted specimens was determined by electron probe microanalysis. An amorphous passive film on the order of 200 Å thick formed on the Al surface in the 95 C etch solution prior to the electrochemical etch. A model for the etch process in which pits were seen to propagate immediately at flaws in this passive surface was supported by the shape and distribution of etch pits after brief etching. Pits propagated under the surface oxide in crystallographically determined directions in both unimplanted and Cu implanted samples. The presence of ion implanted Cu resulted in a smaller number of more highly developed, deeper pits. Capacitance versus voltage and weight loss measurements of highly etched samples indicated that approximately the same amount of overall Al dissolution occurred in all samples. More local etching occurred in the high dose Cu implanted specimens, with significant loss of fine surface structure. Electron probe measurements showed that no change in the total Cu content of the various foils occurred during etching.