Properties of Microplasma Coating on AZ91 Magnesium Alloy Prepared from Electrolyte with and without the Borax Addition

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.

Corrosion and Wear Behavior of TiO2/TiN Duplex Coatings on Titanium by Plasma Electrolytic Oxidation and Gas Nitriding

“…When a capacitor is omitted from the circuit, no current can flow because, when the capacitor is charged, the current will not pass, and the circuit will be cut off. The dense oxide layer on the surface of the titanium also has this effect and, such as a capacitor after being fully charge, disrupts the electrical circuit by reducing the corrosion rate [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ]. Based on the EIS diagrams and the obtained data, it can be concluded that the corrosion resistance of the sample with plasma electrolytic oxidation coating is better than that of the uncoated sample.…”

An Impact of the Recent Developments in Coating Materials and Techniques on the Corrosion Response of AZ91D Alloy: A Review

“…[16] The sunburst plot (Figure 12) represents all the possible coating categories and materials explored by various researchers during the last decade. [67,88,98,100,[113][114][115][116][117][118] The metal-based coatings are popular in composite and singlematerial coatings. However, polymer-based materials are extensively explored in the case of biodegradable and self-healing coatings.…”

“…[45,51,90,138,139] The deposition time of 15 min, 20% duty cycle, 600 Hz frequency, 2 A working current, and 22 AE 2 °C electrolyte temperature are the important optimum parameters reported for AZ91D coating. [116,118,138] In the MAO coating of Mg-alloys, high voltage ranging from 200 to 500 V was used in various studies. [45,51,87,116,136] However, 120 and 140 V were also used in some studies for the MAO of AZ91D alloy for biomedical applications.…”

“…[ 16 ] The sunburst plot ( Figure ) represents all the possible coating categories and materials explored by various researchers during the last decade. [ 67,88,98,100,113–118 ]…”