Abstract
Magnesium alloys, due to their unique properties, low density and high strength properties, are becoming more frequently used in industrial applications. However, a limitation of their use may be the need to ensure high abrasive wear resistance and corrosion resistance. Therefore, magnesium alloys are often protected by applying protective coatings. The paper presents the influence of the modification of the electrolyte composition, with or without the addition of borax, on the morphology (observed by SEM method) and phase composition (analyzed by EDS and XRD) of the formed layers on the AZ91 magnesium alloy, and their abrasive wear (determined with Ball-on-Disc method) and corrosion resistance (evaluated using the immersion method and by electrochemical tests), especially in chloride solutions. It has been clearly demonstrated that the modification of the electrolyte composition significantly impacts the final properties of the protective coatings on the AZ91 alloy formed by the plasma electrolytic oxidation (PEO) process. On the basis of the results, it was found that the new type of PEO coatings with the borax addition, compared to base PEO coatings, showed significantly higher abrasion resistance and an order of magnitude lower corrosion rate.
Highlights
Magnesium and its alloys, due to their density, are classified into the group of so-called “light metals”
Too much additional zinc causes hot brittleness and the formation of microporosity in the alloy, whereas manganese, which is the basic component found in almost all magnesium alloys, does not significantly affect the mechanical properties, but increases the corrosion resistance of magnesium alloys in saltwater, because it limits the negative influence of iron, which is the cause of corrosion [11]
AZ91 magnesium alloy—reference sample AZ91 magnesium alloy covered without the borax addition plasma electrolytic oxidation (PEO) layer AZ91 magnesium alloy covered with the borax addition PEO layer
Summary
Due to their density, are classified into the group of so-called “light metals”. Despite the significant progress in the synthesis of this type of coating, research is still underway on: the dependence of the influence of the composition and microstructure of the substrates [18], the electrolyte used and the process parameters [19], on the formation phenomenon and the final properties of the obtained coating [20]. This method is environmentally friendly, and the procedure is usually performed in solutions that do not contain toxic components [21]. The influence of the modification of the electrolyte composition, with or without the addition of borax, on the morphology and phase composition of the formed layers and their abrasive wear and corrosion resistance, especially in chloride solutions, was analyzed
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