Plasma electrolytic oxidation of AM60 magnesium alloy: Monitoring by acoustic emission technique. Electrochemical properties of coatings

Magnesium alloy AM60 (6% Al) behaviour during Plasma Electrolytic Oxidation (PEO) was monitored by the Acoustic Emission (AE) technique. The process is divided into four stages, each one emitting characteristic acoustic signals. The following physical phenomena could be distinguished: bubbles during the conventional anodising step (stage 1), two discharge regimes, named microarc (stage 2) and arcing (stage 3) and film relaxation phenomena combined with bubbles coalescence inside the porous film after the anodising was stopped (stage 4). The applied DC current density has no visible effect on AE signals. The electrochemical behaviour of anodised samples has been investigated by electrochemical techniques. The anodic film provides a good level of corrosion protection only for a limited period of time. This lack of corrosion protection efficiency is due to the porous and non-perfectly adherent structure of the film.