基于pH响应的镁合金微弧氧化/共聚物水凝胶复合自修复涂层制备及其腐蚀自抑制机制研究

When traditional coating on magnesium alloy is damaged by forces, the filiform corrosion of magnesium substrate will make the coating peel at edge of the damage, and the coating also cannot offer dependable mechanical protection for the release structure of inhibitor, which results in the coating without the self-healing property. These two reasons will cause the serious and rapid corrosion of substrate when the coating is damaged, seriously affecting the service dependability of the material. In this project, it will design an integrated composite coating of micro-arc oxidation (MAO)/hydrogel structure. In the composite coating, the metallurgically bonded MAO layer can restrict the magnesium substrate from the filiform corrosion. On the other hand, the pH response hydrogel can further polymerize in situ in the MAO pore, and form a dependable mechanical structure of releasing inhibitor. Therefore, this composite structure has the self-repair property by releasing inhibitor according to the long-term response to local corrosion. The hydrogel molecula structure can be adjusted through introducing the hydrophobic, polyethylene-glycol-grafting, silane-grafting, which can increase the accuracy of pH response and mechanical stability for the inhibitor-released structure. In the meantime, the use of scanning pH microelectrode and Kelvin probe will investigate the relationship between the local pH value and swelling-inhibition property of hydrogel, study the evolvement rule of local corrosion potential, and reveal the dynamic mechanism of microcosmic corrosion. Finally, the self-healing mode of pH response can lay the theoretical and methodological foundation for the preparation of self-healing coating on Mg alloy.

镁合金传统涂层受外力破损后，基体丝状腐蚀会造成破损边界处涂层剥离，而且涂层自身难以为缓蚀结构提供可靠力学保障，腐蚀抑制能力有限，两方面原因综合作用导致传统涂层破损后基体迅速腐蚀，严重影响材料服役可靠性。针对这一问题，本课题提出微弧氧化（MAO）膜/水凝胶一体化自修复涂层设计，在冶金结合的MAO膜遏制丝状腐蚀的基础上，进一步在膜微孔内原位聚合pH响应水凝胶，形成具有可靠力学保障的微纳缓释结构，长效地响应微区腐蚀，释放缓释剂实现腐蚀自抑制。通过引入疏水单元、聚乙二醇接枝和硅烷接枝调整水凝胶分子结构，提高缓释结构对腐蚀微区pH响应的准确性及其力学稳定性。同时，利用扫描pH微电极、开尔文探针等手段，研究腐蚀微区pH与水凝胶溶胀缓释特性之间的相互作用以及微区腐蚀电位的演变规律，揭示微观腐蚀动力学机制，最终建立基于pH响应的腐蚀自抑制模型，为制备具有破损处腐蚀自修复的镁合金涂层奠定理论和方法基础。

镁合金传统涂层一旦受外力破损后基体迅速腐蚀，影响镁合金部件的服役可靠性，有两方面原因：一、基体丝状腐蚀会造成破损边界处涂层剥离，二、涂层自身难以为缓蚀结构提供可靠力学保障，腐蚀抑制能力有限。针对上诉问题，本项目研制了以微弧氧化膜（MAO）为骨架结构，在膜微孔内原位聚合水凝胶缓释结构的一体化自修复涂层。主要取得以下研究成果：.1）建立暂态自反馈控制技术（TSFC）机理模型，揭示了TSFC模式的高频脉冲均匀化作用对氧化膜微观结构致密化作用，从而制备出高致密微弧氧化膜（C-MAO），其阻抗值高于双向脉冲所制备的膜层1个数量级。C-MAO受外力破损时，破损边缘区域明显抑制丝状腐蚀“丝头”形成及扩展，避免涂层边缘剥离，为构建镁合金自修复涂层提供了先决条件。.2）系统掌握了MAO膜内原位聚合聚丙烯酰胺（PAM）关键工艺参数，揭示水凝胶分子结构对其pH响应溶胀、释放性能的作用规律，形成MAO膜原位聚合水凝胶的控制工艺技术，分别制备了水凝胶负载硝酸铈/MAO（Ce-PAM/MAO）和水凝胶负载LiOH/MAO（Li-PAM/MAO）自修复涂层；.3）揭示自修复涂层的pH响应溶胀缓释特性与破损处腐蚀抑制能力的相互作用规律，Ce-PAM/MAO 和 Li-PAM/MAO涂层可缓释Ce3+和OH-，电化学阻抗分析划痕处钝化膜电阻Rsc相比MAO高一个数量级，表明划痕处在腐蚀环境下逐步形成致密的钝化膜，实现腐蚀自修复。.本项目研究结果为实现镁合金自修复涂层奠定了理论基础，提供了可行性方案，对提高镁合金在武器装备轻量化设计应用过程中服役寿命，保障服役可靠性，具有重要意义。