Features of microarc oxidation of magnesium alloys and corrosion destruction of the resulting coatings

Purpose of this work was to determine the characteristics of coatings formed on magnesium alloys during the process of micro-arc oxidation (MAO) in an electrolyte with minimal content of basic solution components. Additionally, the study aims to identify research directions that can ensure controlled solubility of magnesium alloys with MAO coatings in a corrosive and active environment. Research methods. The study was performed on samples of MЛ5 alloy. The MAO was conducted using an alternating current of 380 V and 50 Hz, along with a battery of capacitors with adjustable capacity. The electrolyte used was a combination of potassium hydroxide and sodium liquid glass. Corrosion tests of the treated samples were conducted in a 3 % aqueous NaCl solution. The surface of the samples after MAO was examined using optical and scanning electron microscopy. Results. The results of research in the field of MAO of magnesium alloys are considered. It is shown that the use of MAO coatings is one of the promising directions for developing methods to control the dissolution rate of magnesium alloy products. The concentration of reagents in the electrolyte and the processing time were minimized. It was found that it is advisable to complete the treatment before the phase of intense sparking. The initiation of the sparking process leads to the damage of the barrier layer by microarc discharges, which reduces the corrosion resistance of the coating. Scientific novelty. It was found that the degree of corrosion damage was minimal for the sample treated for 30 s. The obtained result can be explained by the termination of the MАO process at the moment when a dense coating has already formed at the first stage of the process, but the second stage with the formation of micro-arc discharges, which damage the already formed oxide layer, has not yet begun. Practical value. The results of the study will serve as a basis for further work aimed at creating magnesium alloy products with a controlled dissolution time in a corrosive environment. This is especially relevant for medical products, namely metal fixators for osteosynthesis with a controlled rate of biological resorption.