Sepiolite reinforced PEO layer on AZ 31

The present work deals with the investigation of the incorporation of nanosized ceramic particles (sepiolite) into an oxide layer formed on magnesium alloy AZ31 by plasma electrolytic oxidation (PEO). The actual (true) surface area of the sepiolite particles was determined to be 300 m2 g-1. The particles were exclusively electrostatically stabilized in the used electrolyte without visible sedimentation, at least over 27 days. Using a current controlled pulse regime, the particles are incorporated into the oxide layer simultaneously to the PEO process. The study clearly reveals that the movement and deposition of the particles is based on electrophoresis. Considering the measured mobility of the particles of μ ≈ 6 μm cm V-1 s-1 and a very low field strength in the electrolyte (0.4 V cm-1) the particles velocity was calculated to υ ≈ 2.4 μm s-1. The mass of deposited sepiolite was estimated to approximately 1.2 mg cm-2 under the chosen conditions. The fixation of the deposited particles is caused by sintering due to the heat development of the plasma discharge events.