Preparation of a thick sponge-like structured amorphous silica ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in TEOS solution

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 mu m. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 mu m between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50-60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5-3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si3N4 friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 x 10(-5)A center dot cm(-2) to 1.239 x 10(-7)A center dot cm(-2), while extending the passivation region from 0.322 V to 1.032 V.