Mg-Ca合金阳极氧化膜降解机制的新见解

曾荣昌

    一般地，微弧氧化膜有两种孔隙：通孔和非通孔。通孔又分为开孔和孤立孔或盲孔。开孔在最外层，直接暴露于溶液；盲孔在涂层中间，在初始阶段不与溶液直接接触；通孔则穿透整个氧化膜，因而导致溶液与基体金属直接接触。因此，在镁合金阳极氧化膜腐蚀过程当中，每种孔隙起着不同的作用。尤其是，通孔引起所谓的电偶效应，即，MAO涂层与基体形成微电偶电池。另外，第二相与基体相也产生微电偶电池。因而，澄清通孔在阳极氧化膜整个孔隙中的作用是非常重要的。很遗憾的是，有关通孔率对镁合金MAO膜腐蚀的影响报道还少见。    

   目前，MAO膜腐蚀机制的主要争论是理解非通孔和通孔对腐蚀的竞争性贡献。该项工作的目的是建立MAO膜的物理性能（如，孔径、孔隙率和厚度）和耐蚀性能的关系，以新的视角来研究孔隙率的影响和非通孔和通孔在腐蚀当中的作用，最终获得对MAO 涂层化学腐蚀和Mg-Ca合金电化学腐蚀的全面理解。

Title: Degradation mechanism of micro-arc oxidation coatings on biodegradable Mg-Ca alloys: The influence of porosity

题目：Mg-Ca合金微弧氧化膜降解机制：孔隙率的影响

Abstract  

The morphology, porosity and corrosion resistance of MAO coatings on as-extruded Mg-Ca alloys were analysed using SEM, XRD, EDS and electrochemical tests. Theroles of non-through and through-pores in the MAO coating were identified. The results demonstrated that the corrosion resistance of the MAO-coated Mg-Ca alloys is related to the corrosion resistance of the substrates, the porosity of the MAO coating and the galvanic effect. Chemical and electrochemicalcorrosion alternately occurred on the MAO coatings. The alternating chemicaland electrochemical corrosion mechanisms for the MAO coating are discussed.

摘要

    利用SEM、XRD、EDS和电化学试验研究了挤压态Mg-Ca合金微弧氧化膜（MAO）的形貌、孔隙率和耐蚀性能。鉴别了微弧氧化膜中非通孔和通孔的作用。研究结果表明，Mg-Ca合金微弧氧化膜的耐蚀性与基体耐蚀性、MAO的孔隙率和电偶效应有关。MAO膜交替地出现化学腐蚀和电化学腐蚀。最后讨论了MAO膜的化学腐蚀和电化学腐蚀机制。

Keywords 关键词

• Metals and alloys;    金属和合金
  

• Thin films; 薄膜

• Corrosion; 腐蚀

• Oxidation; 氧化

• SEM 扫描电子显微镜

Graphical abstract（图片摘要）

Highlights（亮点）

•The change in open circuit potentials leads to alternating degradation mechanisms.

开路电位的变化导致降解机制的改变。

•Degradation mechanisms include chemical and electrochemical corrosion.

降解机制包括化学腐蚀和电化学腐蚀。

•Chemical corrosion of the coatings may be related to the non-through pores.

阳极氧化膜的化学腐蚀涉及非通孔。

•Electrochemical corrosion is due to through-pores and micro-cracks of the coating.

电化学腐蚀是因为涂层中的通孔和微裂纹。

•Through-pores in the microarc oxidation coating designate a galvanic effect.

微弧氧化膜中的通孔指示电偶效应

    论文近期在线发表在《Journal of Alloys and Compounds》(695, 2017: 2464–2476) 。

Free access to the article, and valid for 50 days, until February 08, 2017。

相关文献：

【1】Rongchang Zeng, Wei-Chen Qi, Hong-Zhi Cui, Fen Zhang, Shuo-Qi Li,En-Hou Han. In vitro corrosion of as-extruded Mg-Ca alloys—The influence of Ca concentration. Corrosion Science, 2015, 96 (2015) 23–31.

【2】C.L. Liu, Y.J. Wang, R.C. Zeng, X.M. Zhang,W.J. Huang, P.K. Chu. In Vitro Corrosion Degradation Behaviour of Mg-Ca Alloy in the Presence of Albumin, Corrosion Science, 52(2010)3341-3347.

【3】Chun-Yan Zhang, Rong-Chang Zeng, Cheng-Long Liu, Jia-Cheng Gao. Comparison of calcium phosphate coatings on Mg–Al and Mg–Ca alloys and their corrosion behavior in Hank's solution, Surface and Coatings Technology, 204(21-22) 2010: 3636-3640.