The Influence of Negative Voltage on Corrosion Behavior of Ceramic Coatings Prepared by MAO Treatment on Steel

Abstract

In this study, the 10B21 steel was treated by micro-arc oxidation (MAO) in the electrolyte consisting of aluminate and phosphate to enhance its corrosion resistance. The effect of negative voltage on corrosion resistance of the MAO coating obtained has mainly been analyzed through their phase composition, microstructure, interfacial bonding strength, salt spray and electrochemical testing. The result indicates that with negative voltages applied to the MAO coating, Fe-Al transition layers arise between coating layer and matrix. Furthermore, different negative voltages bring forward different α-Al2O3 contents contained in the MAO coatings and when it reaches −100 V, the amount of α-Al2O3 appears as the largest. The surface porosity of the coating was also significantly decreased. In addition, the corrosion current density of the coating is only 3.64 μA·cm−2, which is two orders of magnitude lower than that of the substrate. After 72 h of salt spray corrosion, it is found that the coating substrate is less corroded when the negative voltage of 100 V is applied. Therefore, −100 V has been proven as the optimum performance for improving the corrosion resistance of 10B21 steel.

Study of Coating Growth Direction of 6061 Aluminum Alloy in Soft Spark Discharge of Plasma Electrolytic Oxidation

“…As is known from previous studies [ 23 , 24 ], the relative phase contents of α-Al 2 O 3 and γ-Al 2 O 3 in the PEO ceramic layer can be obtained by the ratio of the maximum diffraction peak intensity of α-Al 2 O 3 to that of γ-Al 2 O 3 , I α /I γ , and the results are shown in Table 2 . From the beginning of the transition to soft spark discharge (a) to the completion of the transition to soft spark discharge (b), the relative phase content of Al 2 O 3 increases while I α /I γ decreases.…”

“…At 100 s, only a NaⅠ peak (589.5 nm) appeared; at 800 s, on the basis of the original peaks, an OⅡ peak (304.2 nm), an AlⅠ peak (396.1 nm) and a Hβ peak (486.1 nm) appeared; at 1100 s, there appeared a SiⅠ peak (288.1 nm), and the peaks reached their highest values; and at 1500 s, the transition to soft spark discharge was completed and the peaks showed an obvious plunge, with the intensity of the optical emission decreasing by about 90%. As is known from previous studies [23,24], the relative phase contents of α-Al2O3 and γ-Al2O3 in the PEO ceramic layer can be obtained by the ratio of the maximum diffraction peak intensity of α-Al2O3 to that of γ-Al2O3, Iα/Iγ, and the results are shown in Table 2. From the beginning of the transition to soft spark discharge (a) to the completion of the transition to soft spark discharge (b), the relative phase content of Al2O3 increases while Iα/Iγ decreases.…”

Preparation and Performance of Micro-Arc Oxidation Coatings for Corrosion Protection of LaFe11.6Si1.4 Alloy

“…Nevertheless, the copper-formed surface corrosion layer is not as dense as those of other metal oxides, resulting in uneven and loose phenomena that accelerate corrosion. Recently, micro-arc oxidation (MAO) technology has been widely used in the anti-corrosion process of medical magnesium–zinc alloys owing to their dense and uniform coating, which has a good anti-corrosion performance, simple operation, no pollution, and no strict requirements for the appearance of the matrix materials [ 22 ]. At present, micro-arc oxidation technology is mainly applied to metals such as Mg, Al, and Ti, rather than Fe-based alloys.…”

Study on Discharge Characteristics and Microstructural Evolution of PEO Coatings Based on an Al/Ti Tracer Substrate

“…It has a higher operating voltage accompanied by obvious plasma discharge at the anode, by which ceramic-like coatings can be in-situ-fabricated on valve metals (Al, Ti, Mg, etc.) and their alloys [1][2][3][4][5][6]. Metals such as Ti, Al, and their alloys are considered viable candidates for developing implantable materials in the medical field due to their satisfactory biocompatibilities.…”

“…PEO technique [11], which produces oxide coatings on the surfaces of valve metals through in situ reactions, demonstrates the distinct advantage of high adhesion strength. The in situ characteristics and inherent porous ceramic structure of PEO coatings amplify the diversity of their functions, including high wear resistance, corrosion resistance, and thermophysical properties [4][5][6]. Moreover, PEO has emerged as the most promising technique for the preparation of oxide films due to its advantages of low environmental pollution, high coating growth rate, and excellent reproducibility.…”