The Effects of Nano-SiO2 on the Chemical Composition of Layers on Aluminum Alloy by Micro-Arc Oxidation

In this article, a nano-SiO2/micro-arc oxide composite coating layer was prepared on the surface of 7A52 Aluminum alloy by addition of SiO2 nanoparticles into the micro-arc oxidation electrolyte to enhance the performance of the formed oxidative layer. Then, the composite oxidative layer was characterized by X-ray Photoelectron Spectroscopy (XPS) to investigate its elemental and chemical compositions, as well as their respective distributions. The results revealed that at elevated temperatures resulted from micro-arc discharge, the SiO2 in the composite reacted with Al2O3 (the major content of the micro-arc oxidative layer) to form a new compound known as mullite. In addition, the contents of SiO2 and γ-Al2O3 in the inner layer of the oxidative layer were lower than those in the surface layer. This can be explained by the higher temperature in the inner layer which motivated the formation of mullite and α-Al2O3 from SiO2 and γ-Al2O3 respectively during the micro-arc oxidation process.