【作者】 张艳；

【导师】 梁伟；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2008， 硕士

【摘要】 本文采用真空固态扩散渗的方法对AZ91D镁合金进行表面合金化改性处理,在镁合金表面获得合金化渗层。本文探讨了渗铝层的形成机制以及温度、时间等不同工艺参数对渗铝层结构及性能的影响。试验结果表明,温度在405～445℃之间、保温时间在60～90 min之间和真空度在优于10^-2Pa的条件下都可以得到理想的渗铝层,为镁合金表面合金化改性处理的工艺参数优化提供了依据。实验采用光学金相显微镜（OM）及扫描电镜（SEM）观察不同条件下渗铝层的组织形貌,通过能谱仪（EDS）和X射线衍射仪（XRD）分析其成分和结构特征。结果表明,随扩渗温度和保温时间的不同,渗铝层的化学成分,相结构,组织形貌及厚度均发生相应的变化,但所有渗层结构均匀致密,与基体结合良好;渗铝层主要由金属间化合物β-Mg₁₇Al₁₂相组成。显微硬度分析结果表明,渗铝层中金属间化合物的存在提高了试样表面的显微硬度值。表面硬度的提高有利于材料耐磨性的提高,有利于扩大镁及镁合金的应用范围。全浸实验和电化学腐蚀实验结果表明,渗铝层的存在有效地阻隔了腐蚀溶液与AZ91D镁合金基体的直接接触,从而提高了镁合金基体的耐腐蚀性能。同时发现,渗层表面的完整性对提高镁合金材料的耐蚀性非常重要。本文研究结果表明,真空固态扩散渗铝能够实现AZ91D镁合金的表面合金化,获得理想的渗层,有效提高镁合金的表面硬度和耐腐蚀性能,为改善镁合金耐腐蚀性能,探索了一条新的途径。更多还原

【Abstract】 Surface modification treatment was conducted by vacuum solid diffusion aluminizing on AZ91D magnesium alloy.The aluminized coatings were obtained on the surface of AZ91D magnesium alloy.In this thesis,the formation mechanism of the alloyed layers and the effect of the technological parameters（such as the temperature and the time）on the microstructures and properties of the aluminized coatings was discussed.The results showed that an ideal aluminized coating could be formed when treated at 405～445℃for 60～90 min with a vacuum level of better than 10^-2Pa,which offered evidences for the optimization of the process parameters of the surface-alloying modification treatment on magnesium alloy.The microstructure and morphology of the aluminized layers obtained in different conditions were observed through Optical Microscope（OM）and Scanning Electron Microscopy（SEM）,and the chemical composition and structure characteristics were analyzed through Energy-dispersive Spectroscopy（EDS）and X-ray Diffraction（XRD）.It was indicated that the chemical composition,phase structure,morphology and thickness of the surface diffusion layers varies with the different diffusion temperature and different diffusion time.All the aluminized coating is uniform and dense,firmly bonds to the matrix.The intermetallic compoundβ-Mg₁₇Al₁₂phase is a main component of the coating.The microhardness testing showed that the exist of the intermetallic compounds has improved the hardness of the aluminized coating.The higher hardness is meaningful to increase its wearing resistance and extend its use.The immersion testing and the electrochemical testing showed that the direct contact between the solution and AZ91D magnesium alloy is effectively obstructed due to the aluminized coating,which greatly enhances the corrosion resistance of the magnesium alloy.The results show that the corrosion resistance and the microhardness of pure magnesium can be improved by the vacuum solid diffusion,which providing a new way for the surface alloying of magnesium alloys.更多还原