AZ91D镁合金无铬复合涂层的制备与耐蚀性

发布时间：2018-05-27 14:14

本文选题：AZ91D镁合金 + 钼酸盐转化膜　；参考：《西安科技大学》2016年硕士论文

【摘要】：近年来,镁合金因比强度比刚度高、质量轻、延展性良好和高的导热性等诸多优点,被广泛地应用于汽车、航空、电子等领域。但是镁合金有个致命的缺点就是化学性质太活泼,极易在各种环境中被氧化,因此开发镁合金的防护技术对推进镁合金的工业化发展具有十分重要的意义和应用价值。本文以AZ91D镁合金作为研究对象,采用正交实验和单因素实验,确认了钼酸盐转化液体系为:钼酸钠(NaMoO_4)30g/L,温度为50oC,高锰酸钾(KMnO_4)8g/L,处理时间为40min,pH值为5.5。转化膜表面形貌为宽裂纹与窄裂纹镶嵌组合而成,EDS分析表明Mo、Mn含量在宽裂纹区分布多于窄裂纹区;耐点滴腐蚀实验表明转化膜试样比镁基体在腐蚀液中的耐蚀时间延长近11分钟;极化曲线和阻抗谱结果表明转化膜的自腐蚀电流密度为1.32×10-7A/cm2,比镁基体降低了2个数量级,极化电阻为1368.4?·cm2,是镁基体极化电阻的7倍。在转化膜的基础上,采用化学转化与溶胶凝胶技术相结合的工艺,在镁合金转化膜上制备出了杂化涂层,形成复合膜层。复合膜层的结合力达到1级,涂层表面形貌致密均匀无裂纹,腐蚀电流密度比镁基体的降低了3个数量级,极化电阻达到3.03×104?·cm2。采用动电位极化和交流阻抗技术研究了转化膜和复合膜在NaCl溶液中的腐蚀行为。结果表明,转化膜和复合膜在浸泡后期都会出现感抗弧,表现出相似的电化学腐蚀行为,只是耐腐蚀的时间和程度相差较大,复合膜在3.5%NaCl溶液中的浸泡时间长达204h,而转化膜的浸泡时间只有42h。
[Abstract]:In recent years, magnesium alloys have been widely used in automobile, aviation, electronics and other fields because of their advantages such as high specific strength and stiffness, light weight, good ductility and high thermal conductivity. However, magnesium alloy has a fatal drawback that its chemical property is too lively and it is easy to be oxidized in various environments. Therefore, the development of magnesium alloy protection technology is of great significance and application value in promoting the industrialization of magnesium alloy. In this paper, AZ91D magnesium alloy was used as the research object. The molybdate conversion solution system was confirmed as follows: NaMoO 430g / L, temperature 50oC, potassium permanganate KMnO 4g / L, treatment time 40 mins pH = 5.5. The EDS analysis shows that the Mo-Mn content in the wide crack zone is more than that in the narrow crack zone, and the surface morphology of the conversion film is a combination of wide crack and narrow crack mosaic. The corrosion resistance test showed that the corrosion resistance time of the conversion film was 11 minutes longer than that of the magnesium substrate, and the polarization curve and impedance spectrum showed that the corrosion current density of the conversion film was 1.32 脳 10 ~ (-7) A / cm ~ (2), which was two orders of magnitude lower than that of the magnesium substrate. The polarization resistance is 1368.4? cm ~ 2, which is 7 times of that of magnesium matrix. On the basis of conversion film, hybrid coating was prepared on magnesium alloy conversion film by combining chemical conversion and sol-gel technology. The bonding force of the composite film is 1, the surface morphology of the coating is compact and even without cracks, the corrosion current density is 3 orders of magnitude lower than that of the magnesium substrate, and the polarization resistance is 3.03 脳 10 4? cm 2. The corrosion behavior of conversion film and composite film in NaCl solution was studied by potentiodynamic polarization and AC impedance technique. The results showed that both the conversion film and the composite film had similar electrochemical corrosion behavior during the later period of immersion, but the time and degree of corrosion resistance varied greatly. The soaking time of the composite membrane in 3.5%NaCl solution was 204h, but that of the conversion membrane was only 42h.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG174.4

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