引用本文:王东,刘金玉,孙世博,吴方,温玉清,尚伟.镁合金表面微弧氧化/自组装/镍复合涂层的腐蚀过程和机理[J].中国表面工程,2024,37(1):100~109
WANG Dong,LIU Jinyu,SUN Shibo,WU Fang,WEN Yuqing,SHANG Wei.Corrosion Process and Mechanism of Micro-arc Oxidation / self-assembly / nickel Composite Coating on Magnesium Alloy[J].China Surface Engineering,2024,37(1):100~109
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镁合金表面微弧氧化/自组装/镍复合涂层的腐蚀过程和机理
王东, 刘金玉, 孙世博, 吴方, 温玉清, 尚伟
桂林理工大学广西高校表界面电化学重点实验室 桂林 541004
摘要:
镁合金具有很强的活性,在水溶液或潮湿的大气中容易被腐蚀。为了提高镁合金的耐腐蚀性能,首先利用微弧氧化工艺进行微弧氧化,通过乙酸乙酯(C4H8O2)进行自组装,最后化学镀镍,在 AZ91D 镁合金表面制备微弧氧化(MAO)/ 自组装(SAM)/ 镍(Ni)复合涂层。通过形貌结构、电化学测试和腐蚀产物分析研究复合涂层在 3.5 wt.% NaCl 环境中的腐蚀行为,并建立复合涂层的腐蚀过程模型。结果表明:Cl? 的存在加速了腐蚀的发生。复合涂层的腐蚀电流密度与镁合金相比下降 3 个数量级,复合涂层显著提高了镁合金的耐蚀性。复合涂层在盐雾环境中 0~96 h 时,Ni 层表面结构仍然致密。当复合涂层暴露在腐蚀环境中 120 h 后,Ni 层开始被破坏,腐蚀离子进行渗透,形成通道。之后,基体上的 SAM 层和 MAO 层的保护时间缩短。在 144 h 时,腐蚀离子直接穿透了复合涂层,使基体涂层保护失效。研究成果可为该类涂层的开发、制备和应用提供试验依据和理论基础。
关键词:  镁合金  微弧氧化  复合涂层  耐蚀性能  腐蚀过程
DOI:10.11933/j.issn.1007-9289.20221001002
分类号:TG174
基金项目:广西自然科学基金(2020GXNSFAA159011)
Corrosion Process and Mechanism of Micro-arc Oxidation / self-assembly / nickel Composite Coating on Magnesium Alloy
WANG Dong, LIU Jinyu, SUN Shibo, WU Fang, WEN Yuqing, SHANG Wei
Guangxi Colleges and Universities Key Laboratory of Surface and Interface Electrochemistry,Guilin University of Technology, Guilin 541004 , China
Abstract:
Magnesium alloys, which are the lightest metal construction materials used in industry, play a vital role in future development. Magnesium alloys exhibit outstanding qualities such as low density, efficient electromagnetic shielding, and dimensional stability, making them highly valuable across a wide range of applications in automotive, medical, and electronic communication sectors, among others. However, Mg alloys are highly active and readily corrode in aqueous solutions or humid atmospheres. These alloys have limited applications because of their poor corrosion resistance. Composite coatings can improve the defects of a single coating to achieve better substrate protection. To improve the corrosion resistance of magnesium alloys, a micro-arc oxidation (MAO) / self-assembly (SAM) / nickel composite coating was fabricated on the surface of a magnesium alloy (AZ91D), via MAO, self-assembly by ethyl acetate (C4H8O2), and chemical plating with nickel. SEM and EDS were used to characterize the surface morphology and corrosion product content of the corrosion-processed samples. XRD and XPS tests were employed to analyze the changes in the surface material of the sample during corrosion. AFM was used to characterize the surface roughness of the sample during corrosion. Polarization curve and electrochemical impedance spectroscopy was used to assess the corrosion resistance of samples at various corrosion durations. The corrosion behavior of the composite coating in 3.5 wt.% NaCl environment was studied by morphological structure analysis, electrochemical tests, and corrosion product analysis, and the corrosion process model of the composite coating was established. The results show that the presence of Cl? accelerates the onset of corrosion. Polarization curves and impedance tests showed that the corrosion resistance of the MAO / SAM / Ni composite coating was significantly improved compared with that of the magnesium alloy matrix. The corrosion current density of the composite coating decreased by three orders of magnitude compared with that of the magnesium alloy. After 120 h of corrosion, the corrosion current density of the composite coating was still one order of magnitude lower than that of the magnesium alloy substrate, and the electrochemical impedance reached 1.16×104 ?·cm2 . The results indicate that the composite coating significantly improved the corrosion resistance of the Mg alloy. The Mg alloy matrix corrodes within 24 h and generates corrosion products, including MgO and MgCl2, in an environment of 3.5 wt.% NaCl. The corrosion of the MAO / SAM / Ni composite coatings can be divided into three stages, namely early, middle, and late stages. The surface structure of the Ni layer remained dense when the composite coating was exposed to a salt-spray environment for 0–96 h. In the early stages of corrosion, the corrosion resistance of the coating improved, mainly owing to the formation of the corrosion product NiO, on the surface of the coating. As the corrosion time increased, trivalent NiOOH formed on the surface of the coating, and the coating gradually deteriorated. When the composite coating was exposed to a corrosive environment for 120 h, the Ni layer started deteriorating, and the corrosive ions penetrated and formed channels. Subsequently, the protection capabilities of the SAM and MAO layers diminished. After 144 h, the corrosive ions directly penetrated the composite coating, rendering the substrate coating ineffective. Once the outer layer of the electroless nickel plating was compromised, corrosion ions easily penetrated the composite coating, forming MgCl2 corrosion products. The results provide an experimental basis and theoretical foundation for the development, preparation, and application of such coatings.
Key words:  magnesium alloy  micro-arc oxidation  composite coating  corrosion resistance  corrosion process
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