铝阳极氧化膜腐蚀行为的研究

【作者】 赵鹏辉；

【导师】 左禹；

【作者基本信息】 北京化工大学 ， 材料学， 2001， 硕士

【摘要】 铝的阳极氧化膜不仅具有优良耐磨和耐腐蚀性，还具有装饰功能并可用作外部涂层的过度层，在国民经济各部门应用非常广泛。阳极氧化虽然使铝合金耐蚀性提高，但在腐蚀性较强的环境中，侵蚀性阴离子如氯离子以及氧离子，水分子等杂质仍然能够渗透氧化膜并最终引起小孔腐蚀或其他类型的局部腐蚀。现在有关阳极氧化膜的腐蚀机理仍然不够清楚，因此“铝阳极氧化膜腐蚀行为的研究”课题具有重要的理论和实际意义。 本课题利用扫描电镜（SEM），透射电镜（TEM），X射线衍射等方法研究阳极氧化膜的结构，组成和缺陷；用动电位扫描法测定氧化膜的极化行为，采用光学显微镜，扫描电镜（SEM）对腐蚀蚀形貌进行观察，从而研究氧化膜的耐蚀性能。 研究了阳极氧化的电流密度，氧化时间及电解液温度三个工艺参数对氧化膜的显微组织和在1mol／L NaCl溶液中阳极极化行为的影响。综合氧化膜耐蚀性的提高，确定了氧化膜最佳的制备工艺。 对工业纯铝，超硬铝和硬铝的显微组织形貌及膜表面元素含量进行了考察，结果表明：工业纯铝形成的膜比硬铝和超硬铝的膜厚，孔径长；工业纯铝氧化膜均匀致密无空洞，硬铝和超硬铝氧化膜中有空洞的出现；硬铝和超硬铝氧化膜表面相对工业纯铝氧化膜粗糙；三种铝材的氧化膜主要是由非晶态的Al₂O₃组成。 研究了三种铝材氧化膜在1mol／L NaCl的酸，碱及中性溶液中的极化行为，发现工业纯铝氧化膜耐蚀性最好，硬铝和超硬铝的膜耐蚀性依次递减；氯离子浓度的升高，氧化膜的孔蚀电位负移；对未封孔的氧化膜腐蚀机理进行了初步的探讨，认为侵蚀性离子通过微孔向膜内扩散迁移，与阻挡层作用，导致了孔蚀。 四种方法封孔后，氧化膜的形貌组成不同，造成了氧化膜的的腐蚀行为各异。不同体系中电化学行为的实验结果表明：沸水法封孔和重铬酸钾法封孔最佳适用介质环境为含有氯离子的酸性环境；冷封孔法最佳适用介质环境为含有氯离子的北京化工大学硕士学位论文中性与碱性环境;硬脂酸封孔在酸，碱及中性氯离子环境中都有良好的耐蚀性;在lmol几NaOH溶液中，硬脂酸封孔的氧化膜均匀腐蚀电流最小;对氧化膜封孔后的腐蚀机理进行初步性的探讨，认为侵蚀性离子首先与膜表面局部缺陷结合作用，使膜溶解或破裂，然后向阻挡层，铝从体扩散并与之作用，造成孔蚀或其他类型的腐蚀。关键词:铝阳极氧化膜，显微组织，封孔方法，极化行为，腐蚀机理。更多还原

【Abstract】 The anodized oxide films of Al have good wear and corrosion resistance and are often used as a transitional layer of outer coatings. Therefore, the anodized oxide films have wide applications in various departments of the national economy. Although anodizing improves corrosion resistance of aluminum alloy, the aggressive anions, such as Cl-, O2-, and water molecule etc., still penetrate films and cause pitting or other localized corrosion. The corrosion mechanism of anodized oxide films is not understood enough yet, so the subject has theoretical and practical value.The microstructure, morphology, component and defects of anodized oxide films are characterized by SEM, TEM and XRD. The corrosion behavior of oxide films is studied by means of the potentiodynamic polarization method.The influences of current density, time and electrolyte temperature of anodic oxidation on the microstructure and anodic polarization behavior of oxide films in 1mol/L NaCl solution are studied. The technology of anodic oxidation is optimized according to the improvement of corrosion resistance.The microstructure, morphology, component and defects of anodized oxide films on L2, LC4 and LY12 aluminum are investigated. The results show that the thickness and the pores of L2 film are thicker and longer than those of LC4 and LY12 film. In contrast to the no void oxide film of L2, there are some voids in the oxide films of LC4 and LY12. The surface of LC4 and LY12 film is rougher than that of the L2 film. All the films consist of amorphous Al2O3.The polarization behaviors of the three kinds of oxide films are measured in the acid, alkaline and neutral solutions of 1mol/L NaCl. The results show that the corrosion resistance of anodic oxidation films decreases in the order L2> LY12> LC4. The corrosion behaviors are different because of the different thickness of films. With the concentration of CL- increased, the pitting potentials of films are shifted to more negative potentials. The corrosion mechanism of unsealed film is preliminarily explained as follows: aggressive ions diffuse and migrate into the oxide film through the long pores and incorporate with the barrier film, leading to pitting.Because of the different morphologies and components of anodized oxide filmssealed by four methods, the corrosion behaviors of films sealed are variant. The results of electrochemical polarization of sealed oxide films indicate that the corrosion resistance of sealed films is better than that of unsealed films. The sealed films by the boiling water and K2Cr2O7 are resistant to acid environment containing Cl-. The oxide films sealed by means of the cold sealing have better corrosion resistance in neutral and alkaline environment containing Cl". The oxide films sealed by organic acid C18H36O2 show the fine corrosion resistance in the acid, alkaline and neutral environment containing Cl- and the corrosion current is the smallest in 1mol/L NaOH solution. The corrosion mechanism of sealed oxide films is analyzed tentatively: Firstly, the aggressive ions are absorbed and incorporated at the localized defect sites of film surface, making the film dissolved or breakdown. Secondly, the ions diffuse and act with the barrier film or aluminum matrix, causing pitting or other corrosion.更多还原