AZ31镁合金钕基转化膜制备及性能研究

发布时间：2018-01-08 14:28

本文关键词：AZ31镁合金钕基转化膜制备及性能研究　出处：《重庆大学》2015年硕士论文　论文类型：学位论文

【摘要】：镁合金作为一种工程材料,具有比重轻、比强度高、电磁屏蔽性能好等一系列优点,在汽车工业、航空航天和电子产业中有越来越广泛的应用,被认为是21世纪的“绿色工程材料”。但是镁及其合金的电化学活性很高,其较差的耐腐蚀性能严重制约了镁合金产品的应用。有多种方法可以提高镁合金的耐蚀性能,适当的表面处理是经济有效的方法之一。本文对镁合金进行稀土转化处理与溶胶后处理,研究开发出稀土转化膜与复合膜。文章以AZ31镁合金为基体,Nd(NO3)3为主盐,H2O2为成膜促进剂,以点滴实验和动电位极化曲线为评价指标,采用正交实验法和单因素实验法得到了最佳的稀土转化成膜工艺为:Nd(NO3)3浓度5 g/L,H2O2浓度5 ml/L,成膜时间7 min,成膜温度40 oC。以动电位极化曲线为评价指标,经过单因素实验分析,得到了最佳后处理工艺:浸涂次数3次,干燥温度60 oC,干燥时间1 h,烧结温度150 oC,烧结时间0.5 h。采用SEM分析膜层表面和截面形貌,发现钕基转化膜层表面存在微裂纹,在整个膜层内部在三种裂纹,分别是内裂纹,中间裂纹,外裂纹。铝溶胶膜层覆盖在钕基转化膜层上,盖住了钕基转化膜层的缝隙。采用EDS,XPS与XRD分析膜层的成分,结果表明钕基转化膜的主要成分是Nd2O3和少量Mg O;Nd-Al复合膜的主要成分是Nd2O3和Al2O3。开路电位,动电位极化曲线和析氢实验结果说明,钕基转化膜与Nd-Al复合膜可以明显降低AZ31镁合金的腐蚀速率。钕基转化膜覆盖在AZ31基体上,可以有效地阻碍腐蚀介质与基体的接触;Nd-Al复合膜覆盖了钕基转化膜的裂纹,更好地隔绝了腐蚀介质与基体的接触。交流阻抗谱结果表明,AZ31镁合金,钕基转化膜和Nd-Al复合膜的腐蚀过程都可以分为三个阶段:腐蚀前期(腐蚀介质渗透阶段),腐蚀中期(腐蚀的萌生和扩展阶段),腐蚀后期(腐蚀加剧阶段)。
[Abstract]:As a kind of engineering material, magnesium alloy has a series of advantages, such as light specific gravity, high specific strength, good electromagnetic shielding performance and so on. It has been used more and more widely in automobile industry, aerospace industry and electronic industry. It is considered to be a "green engineering material" in 21th century. But magnesium and its alloys have high electrochemical activity. Its poor corrosion resistance seriously restricts the application of magnesium alloy products. There are many ways to improve the corrosion resistance of magnesium alloys. Proper surface treatment is one of the economic and effective methods. In this paper, rare earth conversion film and composite film are developed by rare earth conversion and sol post-treatment. AZ31 magnesium alloy is used as the substrate in this paper. Nd(NO3)3 as main salt H _ 2O _ 2 as film forming accelerator, with drip test and potentiodynamic polarization curve as the evaluation index. The optimum process of rare earth conversion was obtained by orthogonal experiment and single factor experiment. The optimum process was as follows: 5 g / L H _ 2O _ 2 concentration 5 g / L ~ (2 +) H _ 2O _ 2 concentration and 7 min film forming time. The film forming temperature was 40oC. The optimum post-treatment process was obtained by single factor experiment with the potentiodynamic polarization curve as the evaluation index: 3 times of impregnation, 60 OC of drying temperature and 1 h of drying time. The sintering temperature was 150oC and the sintering time was 0.5 h. The surface and cross-section morphology of the film were analyzed by SEM. It was found that there were microcracks on the surface of the neodymium based conversion film, and three kinds of cracks were found in the whole film. The aluminum sol film is covered by the neodymium based conversion film and covers the gap of the neodymium base conversion film. The composition of the film is analyzed by EDS-XPS and XRD. The results show that the main components of neodymium based conversion film are Nd2O3 and a small amount of MgO. The main components of Nd-Al composite membrane are Nd2O3 and Al _ 2O _ 3. The open-circuit potential, potentiodynamic polarization curve and hydrogen evolution experiment indicate that the composite membrane is composed of Nd2O3 and Al _ 2O _ 3. Neodymium based conversion film and Nd-Al composite film can obviously reduce the corrosion rate of AZ31 magnesium alloy. Neodymium based conversion film can effectively block the contact between the corrosion medium and the substrate by covering on the AZ31 substrate. The Nd-Al composite film covers the cracks of the neodymium based conversion film, and better insulates the contact between the corrosion medium and the substrate. The results of AC impedance spectroscopy show that the AZ31 magnesium alloy. The corrosion process of neodymium based conversion film and Nd-Al composite film can be divided into three stages: the early stage of corrosion (permeation stage of corrosion medium) and the middle stage of corrosion (initiation and expansion stage of corrosion). Late stage of corrosion.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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