Plasma electrolytic oxidation coatings in KOH electrolyte and its discharge characteristics

The ceramic coatings on the surface of AZ31 magnesium alloy were prepared via plasma electrolytic oxidation (PEO) of potassium hydroxide electrolyte. The discharge characteristics and the composition of the coatings were studied. The state evolution of the substrate surface during the PEO process were detected by optical emission spectroscopy (OES) and a high speed camera. The results of OES show that in the anodic oxidation stage, light emission could be attributed to electroluminescence because of the "flaws'' of the dielectric barrier layer. The movement of the spectral peak also occurred at the anodic oxidation stage because of different "flaws'' in the dielectric barrier layer. At the transition stage, light emission could be attributed to the ionization species present in the bubbles. At the discharge stage, the main active plasma species in the plasma field were Na, K, Mg, and O_2, which resulted in the light emitting. The coatings were mainly composed of MgO and Mg(OH)(2). (C) 2014 Published by Elsevier B. V.