Effects of SiO2 nanoparticles in electrolytes on growth process and surface properties of alumina coatings formed on 7A52 aluminium alloy by micro-arc oxidation

Micro-arc oxidation (MAO) is an effective approach to improve the properties of aluminium and its alloys by forming ceramic coatings on the surface. However, the oxide layers often have a porous surface structure, which limits their mechanical properties. In this work, in order to enhance the properties of the layers produced by micro-arc oxidation, AI₂O₃ coatings embedded with SiO₂ nanoparticles were produced on 7A52 aluminium alloy by adding SiO₂ nanoparticles into the electrolyte. With the addition of SiO₂ nanoparticles in the electrolyte, the formation rate of AI₂O₃ coating enhanced considerably and the current density through sample surface became much higher than without SiO₂ at the same voltage. Coatings were investigated with X-ray fluorescence spectrometry (XRF), Scanning electron microscopy (SEM), Vickers hardness test, and reciprocating friction and wear test. The XRF results showed that SiO₂ nanoparticles were successfully embedded in the AI₂O₃ coatings. Compared with the AI₂O₃ coatings without SiO₂ nanoparticles, the MAO AI₂O₃ coatings with SiO₂ nanoparticles are much denser and harder, and the wear resistance is also improved significantly. The improvement can be attributed to the enhancement of the surface structure and morphology of the MAO AI₂O₃ coatings embedded with SiO₂ nanoparticles.