Macrokinetics of Plasma Electrolytic Oxidation of AZ91D Alloy

Plasma Electrolytic Oxidation (PEO) produces thick oxide layer on the surface of metals and alloys. If the process is performed in AC mode, two levels of kinetics can be defined. On one hand, during each period of the alternating (50–60 Hz) current cathodic and anodic processes are repeated. The kinetics of these processes can be referred to as the microkinetics. On the other hand, the treatment time for a typical specimen is 30–90 minutes and the kinetical behavior (macrokinetics) on that scale is completely different than the microkinetics. For many practical purposes, the macrokinetics of a PEO process is not only more ready for an experimental study, but also much more useful in the applicative sense.A macrokinetical study of the PEO treatment of AZ91D magnesium alloy is presented. Plausible explanations of the process are discussed and optimal process parameters are determined.