Effect of electrolyte concentration on the tribological performance of MAO coatings on aluminum alloys
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RESEARCH ARTICLE
Effect of electrolyte concentration on the tribological performance of MAO coatings on aluminum alloys Chao Wang (✉)1*, Jun Chen1,2*, Jihua He1, Jing Jiang1, Qinyong Zhang2 1 Clean Energy Materials and Engineering Center, State Key Laboratory of Electronic Thin Film and Integrated Device, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China 2 School of Materials Science and Engineering, Xihua University, Chengdu 610039, China
© Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
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-Al 2 O3 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. Keywords aluminum alloy, micro-arc oxidation, coating, electrolyte concentration, tribological performance
Received August 9, 2019; accepted November 1, 2019 E-mail: [email protected] *
These authors contributed equally to this work.
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Introduction
Al alloys are ideal for applications in the aerospace, automobile, and military industries. However, Al alloys often show poor tribological performance because of their low hardness [1,2]. In order to improve the wear resistance of Al alloys, various surface treatment methods have been developed. Micro-arc oxidation (MAO) is considered to be a promising method for depositing protective films on the surface of Al alloys. This technique has been extensively used for depositing ceramic coatings on the surface of valve metals such as Mg, Al, and Ti and their alloys [3‒ 13]. The in-situ formation of MAO coatings improves the bonding strength of alloys [14] and protects the substrate during the friction process. For Al alloys in
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