Role of Sodium Silicate for Coating Forming on Magnesium Alloys with Micro Arc Oxidation

被引：0

作者：

Sun L. ^{[1
]}

Ma Y. ^{[1
]}

Dong H. ^{[1
]}

An L. ^{[1
]}

Wang S. ^{[1
]}

机构：

[1] State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou

来源：

Xiyou Jinshu/Chinese Journal of Rare Metals | 2020年 / 44卷 / 04期

关键词：

Coating forming; Corrosion resistance; Magnesium alloy; Micro arc oxidation; Sodium silicate;

D O I：

10.13373/j.cnki.cjrm.XY18090038

中图分类号：

学科分类号：

摘要：

AZ91D magnesium alloys were processed by micro arc oxidation (MAO) in electrolytes without and with sodium silicate, respectively. The role of sodium silicate during MAO treatment was investigated and its effect on MAO coatings was analyzed. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to characterize the microstructure and phase composition of MAO coatings, respectively. And the corrosion resistance of MAO coatings was evaluated by electrochemical workstation. The results showed that a complete, uniform coating was obtained during MAO treatment once sodium silicate was added into the electrolyte, and in turn, the coating's compactness was improved and a new phase Mg2SiO4 with excellent properties was generated in the coatings. With addition of sodium silicate into the electrolyte, the solution conductivity increased and the ignition voltage on specimen surfaces decreased during MAO process, which facilitated a breakdown easily developing on specimen surfaces. Further on this foundation, the competing state in terms of the potential levels in different areas would be enhanced on the anode surface under the coactions between the silicate ions and other anions in the electrolyte, which, in turn, accelerated the sparks' moving phenomena around the coatings' surfaces due to the igniting and extinguishing of the sparks appearing alternately on specimen surfaces. Consequently, the macro-scale pits and the micro-cracks caused by the local thermal accumulation had eliminated on the coatings' surfaces. As a result, the corrosion resistance of MAO coatings formed in the electrolyte with sodium silicate was improved obviously by demonstration of the decreasing of the corrosion current density of the coatings with one order of magnitude and increasing of their linear polarization resistance with sixteen times. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.

引用

页码：378 / 386

页数：8

共 24 条

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