Effect of K2TiO(C2O4)2 Addition in Electrolyte on the Microstructure and Tribological Behavior of Micro-Arc Oxidation Coatings on Aluminum Alloy

Micro-arc oxidation (MAO) coatings with different concentrations of K2TiO(C2O4)(2) in the sodium silicate base electrolyte were prepared on 6061 aluminum alloy with the aim of promoting a better understanding of the formation mechanisms and tribological behaviors of the coatings. Scanning electron microscopy (SEM) assisted with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and friction test were employed to characterize the MAO processes and microstructure of the resultant coatings. Results showed that the composition and microstructure of the coatings were significantly affected by the addition of K2TiO(C2O4)(2). A sealing microstructure of MAO coating was obtained with the addition of K2TiO(C2O4)(2). Ti element from K2TiO(C2O4)(2) was only absorbed into the defects of micropores under surface energy in the early stage, while in the later stage, Ti element was predominant in the micropores and distributed on the coatings under plasma discharge to form TiO2. It was demonstrated that Ti and Si elements from the electrolyte could interact with each other during the MAO process and the interaction mechanism was systematically analyzed. Wear resistance of the MAO coatings with K2TiO(C2O4)(2) addition was significantly improved compared with that of the MAO coatings without K2TiO(C2O4)(2) addition.