Self-similar scaling of discharge events through PEO coatings on aluminium

Plasma electrolytic oxidation (PEO) typically involves hundreds to thousands of discharges per square millimetre per second. In the present work, the characteristics of individual discharges are measured and investigated through an experimental survey of over 3.7 million individual events. The parameters considered include the voltage at which a discharge event commences, the peak current to which it develops, the duration of the discharge, and the current–time profile of individual discharges. It is shown that there is a strong correlation between the voltage at which a discharge event commences and the peak current to which it subsequently develops. There are also strong correlations between these characteristics and the duration of the discharges. These correlations show no significant influence of the coating thickness. The current–time profile is similar for most discharges, scaling according to the initiation voltage, suggesting that all PEO discharge events, whether weak or powerful, all develop according to the same physical mechanisms.

► Strong correlation between initiation voltage, discharge lifetime and peak current.
► Current–time plots show sharp cut-off as plasma expands, cools and increases in resistance.
► Observations and calculations made that pave the way for a comprehensive process model.