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.