镁及镁合金表面处理的新工艺研究与应用

【作者】 杨勇；

【导师】 马克毅； 杨荆舟；

【作者基本信息】 昆明理工大学 ， 冶金工程， 2002， 硕士

【摘要】 本文通过在镁合金基体上化学镀镍和电镀锌的试验，对镁合金进行了表面处理研究。研究了镁合金化学镀镍的工艺条件，重点研究了酸洗工艺、浸锌工艺的最佳工艺条件，以磷酸代替了铬酐加三氯化铁的方法酸洗浸蚀，用化学浸锌层和氰化镀铜层、中性镍层相结合，得到了良好的化学镀镍层。 酸洗工序研究表明：各种文献上记载的各种酸洗配方存在较大差异，有的在具体的实验操作中根本就不可能取得成功，而有的则操作非常复杂，时间及工艺条件要求非常严格，因此在实际操作中存在很多困难，本工艺自主确定了一种酸洗配方，即以85％的磷酸在室温下操作，此种方法不仅酸洗效果良好，能得到性能良好的化学镀镍层，而且配制非常方便，适合工业化的生产。 用扫描电子显微镜确定了最佳的浸锌工艺条件，扫描电镜的结果显示：浸锌层随着浸锌时间、浸锌溶液的浓度的增加而不断改善，时间达到15min时，浸锌层能均匀的覆盖基体表面，较好的掩盖镁合金基体的缺陷。浸锌溶液必须保持足够的浓度，否则浸锌表面的腐蚀点将是致命的。 通过HX-1型显微硬度计研究了镀层的硬度和厚度，用日本理学3015型X射线衍射仪分析了镀层的相结构，结果表明，镀层中主要有Cu、Ni、Ni-Cu化合物。相结构的组成主要是Ni-P非晶态相。 以弯曲实验和锉刀实验来测定了镀层的结合力，实验结果表明：镀层的结合力良好，因此镀层的耐蚀性也好。 以中性盐雾试验研究了镀层的磷含量与镀层耐蚀性的关系，可知含磷低的镀层容易受到锈蚀，含磷高的镀层有较高的耐蚀性。 以中性盐雾试验研究了镀层耐蚀性与热处理温度的关系，可知热处理温度愈高，镀件在盐雾试验中愈早生锈。反之，则耐蚀。镀层在200℃以下热处理对耐蚀性影响不大，当热处理温度超过300℃以上时，镀层耐蚀性明显下降。 采用全浸法测定Ni-P合金与1Cr18Ni9Ti不锈钢在不同介质中的腐蚀速率，结果表明，Ni-P合金与1Cr18Ni9Ti相比，在酸性、碱性和氯离子水昆明理工大学工程硕士学位论文摘要2溶液中显示出良好的抗蚀性能，但不耐硝酸、硝酸盐等强氧化性介质的腐蚀。 测定了Ni一P合金镀层硬度随热处理温度的变化曲线，对比了镀态下5.1%P合金和9.5%P合金的磨损量，证明了含磷量为5.1%的镀层抗磨性好。 本文还研究了在镁合金表面电镀锌和锌基合金的新工艺，确定了切实可行的镁合金表面电镀锌和锌基合金的工艺流程。本试验在镁合金化学镀镍前处理工艺的基础上，确定了碱性锌酸盐镀液，主要研究了镀液成分和操作条件的影响，并分析和测试了镀锌层性能测定了镀锌层的各项性能指标。 综合以上结论，我们认为:本试验化学镀镍工艺配方能够达到镁及镁合金表面强化的效果，镍镀层外观良好，平滑光洁，无孔蚀和起皮，在硬度、耐蚀性和装饰性等方面弥补了镁及镁合金基体的缺陷，且工艺流程清楚，配置简单，进一步成熟后能够应用于工业生产;镁合金表面镀锌和锌基合金是镁表面处理的另一种尝试，镀锌层作为保护性镀层能够提高镁及镁合金基体的耐蚀性。更多还原

【Abstract】 The density of magnesium is 1740kg/m3, which is the lightest metal. The weight of magnesium is 1/1.5 of aluminum and 1/4 of zinc when compared at the same volume. In recent years, the consumption of magnesium is enlarged owing to the thought of energy-saving and environmental protection, especially in transportation. In transportation, the lighter weight of vehicle is more and more required. If magnesium alloy can be make up some parts, we can lighten the weight of vehicle largely. Furthermore, magnesium also is the good material to make up hard-disk of computer and electrical equipment. Magnesium also is a kind of good desulphuring agent in iron and steel industry. Because of the increasing consumption in iron and steel industry, the amount of magnesium will increase steadily.But the electrode potential is so negative (Eo=-2.34v) and the ratio of PB is 0.79 that it can not produce protective oxidation film like aluminum. Therefore, the anti-corrosion of magnesium is so poor that it is apt to corrosion in most environment. In order to apply magnesium in industry, we must treat it by surface processes.To improve the performance of magnesium, the surface treatment means are: chemical oxidation process, electrochemical oxidation process (anodic oxidation process, coloring, chromate coating treatment. But methods as above all have various limitation.Electroless nickel process is an effctive surface treatment means, especially for difficult-to-dump metal such as magnesium, aluminum and zinc. According to the relevant documents, there is hardly successful example by electoless nickel plating on magnesium. Therefore, electroless nickel on magnesium is a new research direction and has large development room. If this process succeed, it must propel the development of other electroless treatment means.According to the experiment of electroless nickel on magnesium, we studied the process condition, especially the importance of pretreatment, acid wash process, zinc-dipping process. In our process, we use phosphor acid insteadof chromium trioxide and ferric chloride, and use layer of dipping zinc, cyanide copper and nickel as bottom. Then we got excellent coating.The study of acid wash procedure indicates: the various ingredients and conditions in documents took on large difference. Some of them cannot succeed at all, and the other methods need complicated operational requirement. Therefore, processes as above cannot apply to industry conveniently. Aiming to this problem, we decided a new acid wash ingredient independently, which we washed magnesium in 85% phosphor acid at room temperature. This process can not only lead to excellent coating, but preparation is convenient, which is suitable for industrial production conveniently.Optimal zinc-dipping process conditions were decided by SEM (Scanning Electron Microscope). SEM results show that, the performance of zinc coating gets better along with the increasing of time and concentration of dipping-zinc solution. When the time reached 15 minutes, the zinc coating can cover the surface of magnesium and faults inside the magnesium evenly. Enough concentration of zinc-dipping solution is required, else the dots on surface due to corrosion are fatal.Hardness and thickness of coating were decided by HX-1 microscopic hardness meter, and phase structure was decided by Japan Scientific 3015 X-ray diffraction meter. Results show that, there are nickel, copper and nickel-copper compound in coating, which are mainly Ni-P non-crystal phase.Adhesive stress was decided by bending experiment and file experiment, too. Results show that, coating has good adhesive stress, so it has excellent anti-corrosion performance.According to above experimental results, we reached a conclusion that, we can get excellent adhensive-stress coating throught this process, which has smooth surface, no bubble and make up the fault of magnesium in hardness, anti-corrosion and decoration. In a word, this process is practicable.更多还原