Effect of electrolyte concentration on the tribological performance of MAO coatings on aluminum alloys

Abstract

Micro-arc oxidation (MAO) is an efficient approach to improve the hardness, wear resistance, and other properties of aluminum alloys. In order to investigate the effect of the electrolyte concentration on the properties of MAO coatings for LY12 alloy, the voltage variation during the MAO process was recorded. The surface morphologies and phase compositions of the coatings produced with different electrolytes were investigated using scanning electron microscopy and X-ray diffraction, respectively. The roughness and thickness of the coatings were measured using a pocket roughness meter and an eddy-current thickness meter, respectively. The tribological performances of the coatings were investigated against GCr15 bearing steel on a ball-on-disc wear tester in open air. The results showed that with an increase in the Na₂SiO₃ content, the working voltage of the MAO process decreased, the roughness and thickness of the coatings increased significantly, and the relative content of the α-Al₂O₃ phase decreased. With an increase in the KOH content, the working voltage decreased slightly, the roughness and thickness of the coatings increased slightly, and the α- and γ-Al₂O₃ phase contents remained unchanged. The friction coefficient and wear rate of the coatings increased with an increase in the Na₂SiO₃ and KOH concentrations. A decrease in the porosity and roughness and an increase in the α-Al₂O₃ content of the coatings reduced their wear mass loss.

Key words： aluminum alloy; micro-arc oxidation; coating; electrolyte concentration; tribological performance

Acknowledgments

This work was supported by the China Postdoctoral Science Foundation Funded Project (No. 2016M602668), the Fundamental Research Funds for the Central Universities of University of Electronic Science and Technology of China (No. ZYGX2015J029), the Project of the Science and Technology Department in Sichuan Province Supporting Plan (No. 2016JQ0022) and the National Natural Science Foundation of China (Grant No. 51501156).

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