Abstract
Effect of V2O5 additive in silicate-containing electrolyte on AZ91D magnesium alloys treated by micro-arc oxidation (MAO) technology under different loading voltages was investigated. The results showed that vanadium was well up-taken into the coating chemically. Moreover, a new phase of MgV2O4 with spinel structure was obtained in MAO coatings due to V2O5 added into the electrolyte. The MgV2O4 phase was responsible for the coatings exhibiting brown color and also was beneficial to improving the anti-corrosion property. In spotting tests, the corrosion resistances of coatings prepared under the high voltage are about 6–9 times higher than those of the low voltage because of the thicker coatings of the former. In potentiodynamic polarization tests, the coatings’ corrosion resistances were improved with the addition of V2O5, which was more significant under the low voltage than that under the high voltage. When the concentration of V2O5 was 0.2 g/L, the corrosion current density of the coating was the lowest, which means that the coating’s corrosion resistance under the low voltage is the best. Hence, it is necessary to carry out targeted design of the coating’s microstructure according to the different applications.
Highlights
Magnesium and magnesium alloys exhibit superior advantages in various applications such as aviation, transportation, and 3C products, due to their outstanding properties like low density, high specific stiffness, and strength to weight ratio [1]
In order to study the effect of V2 O5 on the coating and further understand the corrosion mechanisms in different corrosive media, two types of coatings were prepared on AZ91D Mg alloys in micro-arc oxidation (MAO) electrolyte with V2 O5 additive under two loading voltages
A brown coating was obtained on the surface of AZ91D magnesium alloy due to V2 O5 added into the electrolyte, and the higher the voltage was, the darker the color of the coating turned out to be
Summary
Magnesium and magnesium alloys exhibit superior advantages in various applications such as aviation, transportation, and 3C products, due to their outstanding properties like low density, high specific stiffness, and strength to weight ratio [1]. During the MAO process, the localized instantaneous high temperature sintering of the oxide promotes the formation of the ceramic-like coatings with compact structure, good adhesion with substrate, superior corrosion resistance, and excellent comprehensive performance [2,3,4,5]. For the past few years, vanadium pentoxide, one of the most common vanadic oxides, was mainly used as an additive for the improvement of the wear and corrosion resistances of the substrate in various surface treatment processes [23,24,25]. In order to study the effect of V2 O5 on the coating and further understand the corrosion mechanisms in different corrosive media, two types of coatings were prepared on AZ91D Mg alloys in MAO electrolyte with V2 O5 additive under two loading voltages. The results and corrosion mechanisms in acidic and neutral chloride corrosion environments were discussed, and were expected to enhance the coating’s corrosion resistance under different application scenarios
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