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ABSTRACT
Plasma electrolytic oxidation (PEO) coating with NaAlO2 and KOH electrolytes was applied on the surfaces of as-cast AM60 (PEO-AM60), 7 vol.% Al2O3 fibres/AM60 (PEO-7FC) and 7 vol.% Al2O3 fibres + 3 vol.% Al2O3 nano-sized particles/AM60 (PEO-MHNC-7F3NP) to improve their corrosion resistance. The SEM and EDS analyses indicated that the PEO coating process formed a porous and dense layer on the substrate surface, as well as MgAl2O4 was the major concentration of the coating. The thickness of PEO coating on the 7FC and MHNC-7F3NP composites was slightly less than the coating on the AM60. The electrochemical corrosion tests were carried out in 3.5% NaCl aqueous solution at room temperature for investigating the corrosion behaviour of the as-cast AM60 and the composites after applying the PEO coating. The PEO coating increased the corrosion resistance of the AM60 alloy and the 7FC and MHNC-7F3NP composites to 342.81, 301.73 and 290.44 from 4.07, 2.08 and 1.88 kΩ∙cm2. By comparing the corrosion test results of the coated AM60 and the composites with those of the uncoated counterparts, it was found that the PEO coating significantly improved the corrosion resistance by up to 154 times. The addition of nano-sized particles barely increased the corrosion rate of the composite.
Acknowledgements
The authors would like to take this opportunity to thank the Natural Sciences and Engineering Research Council of Canada for supporting this work. It is acknowledged that the original work of this article was presented in a Master thesis prepared by the authors, Xinyu Geng, under the supervision of Professor Henry Hu at the University of Windsor in 2019.
Disclosure statement
No potential conflict of interest was reported by the author(s).