Electrochemical reactivity of laser-machined microcavities on anodised aluminium alloys

The electrochemical reactivity of laser-machined microcavities on anodised aluminium alloys vas investigated. Excimer Pulse laser (308 nm) depassivation of both absorbing and transparent oxides was carried out in aqueous electrolytes while simultaneously recording the current in an electrochemical potentiostatic three-electrode set-up. Laser irradiation of the absorbing oxide resulted in ablation, whereas the transparent oxide was delaminated by the ablation action of the underlying alloy substrate (spallation). Current transients could be related to ion-conducting flaws generated mechanically in the shock-affected zone (SAZ). Ionic transport through the growing oxide or through the flaw channels controlled the repassivation rate. The repassivation current transients was modelled by a simple equivalent circuit consisting of a capacitor and a resistance in series. The behaviour of the derived resistance values describes the ion conduction rate in cracks or of growing oxide phases. The potential dependence of capacitance during the ablation of the alloy substrate suggests that the dielectric properties of the regenerated oxide films depend drastically on the formation kinetics. (C) 2003 Elsevier Ltd. All rights reserved.