**Alexander Sobolev, Alexey Kossenko and Konstantin Borodianskiy \***

Department of Chemical Engineering, Ariel University, Ariel 40700, Israel; sobolev@ariel.ac.il (A.S.); kossenkoa@ariel.ac.il (A.K.)

**\*** Correspondence: konstantinb@ariel.ac.il; Tel.: +972-3-9143085

Received: 6 November 2019; Accepted: 27 November 2019; Published: 1 December 2019

**Abstract:** The micro arc oxidation (MAO) process has been applied to produce ceramic oxide coating on Ti-6Al-4V alloy. The MAO process was carried out at the symmetric bipolar square pulse in electrolyte containing Na2CO3 and Na2SiO3. The effect of current frequency on the surface morphology, the chemical and the phase compositions as well as the corrosion resistance was examined. Morphology and cross-sectional investigation by electron microscopy evaluated more compacted and less porous coating produced by high current frequency (1000 Hz). This alloy also exhibited a high corrosion resistance in comparison with the untreated alloy. Additionally, the alloy subjected to MAO treatment by a current frequency of 1000 Hz showed a higher corrosion resistance in comparison with alloys obtained by lower current frequencies. This behavior was attributed to more compacted and less porous morphology of the coating.

**Keywords:** micro arc oxidation; current pulse frequency; Ti-6Al-4V alloy; titanium oxide; corrosion resistance
