Corrosion Tests of Oxide-Ceramic Coatings Formed by Microarc Oxidation
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Vol. 61, No. 2, July, 2020
CORROSION TESTS OF OXIDE-CERAMIC COATINGS FORMED BY MICROARC OXIDATION N. S. Chernyshov,1 Yu. A. Kuznetsov,1 M. A. Markov,2 A. V. Krasikov,2 and A. D. Bykova2,3 Translated from Novye Ogneupory, No. 4, pp. 51 – 55, April 2020.
Original article submitted December 23, 2019. The results of experimental studies of the corrosion resistance of aluminum and its alloys modified with ceramic coatings based on the microarc oxidation method in some aggressive environments are presented. The mechanism of destruction of the coating is considered. Recommendations on increasing corrosion resistance are given. Keywords: corrosion resistance, alumina-ceramic coatings, microarc oxidation (MAO), aluminum alloys, magnetron sputtering.
Aluminum parts with a MAO-modified surface can undergo corrosion damage due to the penetration of an aggressive medium into the through-pores of the oxide-ceramic coating [1, 5, 13, 14]. The purpose of this work is to determine the corrosive effect of some aggressive media on an aluminum alloy with a porous protective ceramic coating formed by MAO in a silicate-alkaline electrolyte.
INTRODUCTION Aluminum alloys possess important operational properties such as high strength combined with low density, satisfactory corrosion resistance, and high thermal conductivity. Therefore, these alloys are widely used in mechanical engineering, including for the manufacture of parts of modern light engines in contact with cooling chemically active liquids. In relation to the parts of engine cooling systems made of aluminum alloys, there are several standard ways to combat corrosion: – reducing the aggressiveness of the medium by introducing corrosion inhibitors; – surface protection with non-corrosive material. It is known that microarc oxidation (MAO) of aluminum alloys leads to the formation of oxide-ceramic coatings with high functional characteristics. In particular, such coatings are chemically inert and do not conduct electric current [1–10]. In industrial MAO of aluminum alloys, the most widely used is a combined silicate-alkaline electrolyte of the KOH Na2SiO3 type. However, due to the physical features of the MAO process, high open porosity is inevitably formed in the coatings [11, 12]. These may be through-pores, i.e., reaching the base metal of the substrate, or closed prosed. 1 2 3
MATERIALS AND METHODS OF RESEARCH Microarc oxidation of aluminum alloys was carried out using an IPT-1000 MAO unit. The installation consists of a power source and a control unit, an electrolytic bath with a fastening system for parts and a protective fence. The electrical part of the installation includes a power unit and a unit for control and measurement of the process parameters. For MAO, a standard silicate-alkaline electrolyte of the following composition was selected: potassium hydroxide with a concentration CKOH = 2 g/L, sodium silicate with CNa2SiO3 = 9 g/L, and the rest is water. The process was carried out under constant anode current with a density of 20 A/dm2, the duration of the proc
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