摘要为了对 AZ91D 镁合金耐蚀性进行研究，本文通过查阅相关资料，在最佳条件下对 AZ91D 镁合金进行热扩散渗锌后,进行表面渗层的测试和在不同 PH 值溶液中的腐蚀性 能研究。本文的热扩散渗锌的工艺条件是：加热时间 40min，加热温度 315℃，保温 时间 2h，环境为真空状态。在真空钼丝炉中得到渗层后，用电镜、XRD 衍射仪等对渗 锌层截面厚度、表面结构和成分进行分析，从而分析渗锌层的耐腐蚀性能。另外采用 失重法，宏观和微观腐蚀形貌对比法，硬度测试对比法，电化学腐蚀法对普通镁合金 试样和热扩渗锌试样在不同 PH 的 NaCl 溶液中的腐蚀性能进行测试、对比和分析。83557

研究结果发现，对 AZ91D 镁合金进行热扩散渗锌处理后，由于表面渗层结构比原 先的氧化膜致密许多可以阻挡外界腐蚀物质，而且经过物相分析测定出渗层表面主要 相结构是 MgZn2、Mg2Zn7 和 Mg，MgZn2 和 Mg2Zn7 的电位比镁合金要正很多不易发 生电化学腐蚀，因此可以提高镁合金的耐腐蚀性能。经过失重法和腐蚀形貌对比观察 发现热扩散渗锌镁合金在酸性，碱性，中性 NaCl 溶液中都可以提高耐腐蚀性能，但 在酸性和碱性溶液中耐腐蚀性能提高有限。硬度测试也发现在中性溶液中硬度下降程 度较小，表面渗层完好，在酸性和碱性溶液中渗层结构破坏严重，硬度下降程度较大， 接近基体。电化学腐蚀测试发现热扩渗锌镁合金试样在中性溶液中腐蚀电位最小，腐 蚀电流最大，耐腐蚀性能最好，PH 值偏离中性越远腐蚀电位越大，腐蚀电流越小， 耐蚀性越差。

各项结果表明对 AZ91D 镁合金进行热扩渗锌，可以显著提高耐腐蚀性能，但溶液 PH 值越偏离中性，耐腐蚀性能提高程度越小。

毕业论文关键词：AZ91D 镁合金；渗锌；耐腐蚀性能；不同 PH 溶液

Abstract In order to study the corrosion resistance of AZ91D magnesium alloy,this article through access to relevant information, testing surface alloying layer and studying the corrosion resistance in different PH solution after AZ91D magnesium alloy of thermal diffusion  seep  -age  zinc  under  optimum conditions。 The  best  condition  of the Thermal

diffusion seepage  zinc is here  : the heating  time is 40min,  heating temperature  310   ℃ ,

holding time 2h, vacuum environment。After obtained the diffusion nitrided layer in a vacuum furnace molybdenum wire, analyzing the thickness of the zinc layer ,the surface structure of the zinc layer and the surface composition of the alloying layer to study the corrosion resistance of AZ91D magnesium alloy by using the electron microscopy,and the XRD diffraction。 Then using the method of weight loss, comparison the different of the macroscopic and microscopic corrosion morphology,hardness testing comparison, electrochemical corrosion to test the the corrosion resistance of AZ91D magnesium alloy of thermal diffusion seepage zinc in the NaCl solutions with different sample of PH。

The results found that after the AZ91D magnesium alloy thermal diffusion seepage zinc processing, the surface diffusion layer structure can block many external corrosive substances due to it’s     more dense than the original oxide film , and the main phase of

permeation  layer  surface  structure  is  the  MgZn2  、 Mg2Zn7   and  Mg  after  the   phase

analysis 。the potential of MgZn2  and Mg2Zn7   than magnesium alloy being a lot less prone to electrochemical corrosion, it is possible to improve the corrosion resistance of magnesium alloy。 After weight loss and corrosion morphology was observed comparing the thermal diffusion seepage zinc magnesium alloy in acidic, alkaline, neutral NaCl solution can improve the corrosion resistance, but the corrosion resistance in acidic and alkaline solution can be improved is limited。 Hardness test also found that in neutral solution lesser extent decreased hardness, surface diffusion layer intact, in acidic and alkaline solutions severely damaged the structure of the diffusion layer, the larger the degree of hardness decline, approaching the base。 Electrochemical corrosion testing found that thermal diffusion zinc magnesium alloy samples in neutral solution  minimum corrosion potential, corrosion current largest, the best corrosion resistance, PH  value neutral deviate farther the greater the corrosion potential, corrosion current smaller resistance erosion worse。