Plasma electrolytic oxidation (PEO) is a Novelmethod of oxidation treatment whichin-situ forms ceramic coatings on the surface of light metals like Al alloysunder plasma conditions and improves the properties like wear and corrosionresistance of the surface. The characteristics of PEO coatings can beinfluenced by two main factors: the electrolyte composition and applied currentso that the coating propertises can controlled by change in the electrolytecomposition and applied current regime. However using of the appropriateadditive and current mode can lead to creating the coating with optimalproperties and features. In this study, PEO coatings on 7075 Al alloy wereprepared in both simple silicate based electrolyte and at the presence ofpotassium titanium oxalate (K 2 [TiO(C 2 O 4 ) 2 ])additive varying from 0.5 to 3 g.L -1 with needle like currentwaveform. the results showed for the coating produced in the base electrolyte,crystalline ?-Al2O3 was the main phase, while the coatings formed in thepresence of K 2 [TiO(C 2 O 4 ) 2 ]consisted of TiO 2 . A pancake structure and pore band was observed onsurface and substrete/coating interface for all coating produced under needlelike waveform respectively thus the current waveform plays a more importantrole in the morphology (pores and cracks ,etc) of the coating. To determine the appropriate waveform theresearch was continued by examining current regime with 3 g.L -1 K 2 [TiO(C 2 O 4 ) 2 ]additive in electrolyte bath. Therefore, this work showed while Ti element hascooperated in coating and anatase and rutile phases of TiO 2 have been formed. Moreover by applying bipolar waveform and controllingcathodic pulse time, the strong plasma discharges with high temperature spikescould be eliminated and form a volcano-like surfacemorphology and hence the quality of the coatings was considerably improved. Thecoating formed at bipolar regime with a longer cathodic pulse time due to itscompactness and thickness showed better corrosion and tribological propertiesthan PEO coatings formed at unipolar current regime thatin this waveform the structure has been changed and a foam feature and largepores was detected on the surface and substrate/coating interface of the coatings Keywords: Plasma Electrolytic Oxidation (PEO), 7075 Alalloy, Potassium titanium oxalate, Pulsed current waveform, corrosion, tribocorrosion
