Corrosion protection of thickness reduced plasma electrolytic layers on AZ31

In the present study plasma electrolytic oxidation of magnesium in fluoride free alkaline solution were used to form thin oxide layers with high corrosion protection. The relation between potassium hydroxide and sodium silicate was varied in the electrolyte. The plasma electrolytic process was performed as current controlled unipolar pulse technique. The microstructure of the formed layers were investigated by X-ray diffraction and scanning electron microscopy. The electrochemical behavior was studied by linear sweep voltammetry and impedance spectroscopy. The thickness of the formed oxide layers was in the range of 1-2 µm. The surface morphology strictly depends on the electrolyte composition. Oxide layers formed in an electrolyte with the lowest relation KOH: Na2SO3 show the best performance in view of corrosion protection.