【作者】 李玲玲；

【导师】 程英亮；

【作者基本信息】 湖南大学 ， 材料加工工程， 2008， 硕士

【摘要】 本文采用一种环保型微弧阳极氧化电解液对AZ91、AZ31和AM60镁合金的微弧氧化工艺进行研究,该电解液的组分为氢氧化钠100 g·L^-1,硅酸钠60 g·L^-1,四硼酸钠20 g·L^-1和柠檬酸钠50 g·L^-1,得到了具有较好防护性能的微弧氧化膜,同时对不同牌号镁合金及其表面阳极氧化膜的腐蚀电化学行为进行了较为详细的研究。最后,还对本配方得到的微弧氧化膜和一类运用较广的稀溶液配方中得到的微弧氧化工艺进行了对比研究。本研究的微弧阳极氧化为恒流阳极氧化技术,通过改变电流密度、时间等工艺参数,在AZ91、AZ31和AM60镁合金上分别制备了不同性能的微弧氧化膜。利用电化学阻抗谱和极化曲线技术对所得氧化膜的耐腐蚀性进行测试,研究处理时间,电流密度等因素对镁合金阳极氧化膜耐腐蚀性能的影响。结果表明AZ91和AZ31镁合金在电流密度20mA?cm-2、微弧氧化时间40min时,所得的微弧氧化膜的耐腐蚀性能最好;对于AM60镁合金,当电流密度20mA?cm-2、微弧氧化时间为50min时,所得的膜层的耐蚀性能最好。采用SEM、XRD和EDS研究了三种镁合金得到的氧化膜的微观结构和成分,微弧阳极氧化膜层呈疏松多孔结构,膜层的成分都是MgO和Mg₂SiO₄。利用测厚仪对各种工艺条件下获得的微弧氧化膜的厚度进行测量,氧化膜的厚度分别随时间和电流密度线形增加。除此之外,还研究了氧化膜的厚度与耐蚀性之间的关系,结果表明存在一个耐蚀性最优的膜层厚度。利用中性盐水浸泡试验和电化学阻抗谱技术对三种镁合金的基体和微弧氧化试样进行测试,探讨其腐蚀机理,结果表明本研究选用的三种镁合金阳极氧化膜层的耐腐蚀性的大小秩序与其基体的耐腐蚀性秩序相同。腐蚀试验中,基体合金试样的表面完全被腐蚀,而微弧阳极氧化膜层的腐蚀方式主要为点蚀,这表明微弧氧化后合金的耐腐蚀性能得到很大的提高。最后,本文对比了本研究（浓溶液）得到的阳极氧化膜和5g·L^-1 NaOH、15g·L^-1Na₂SiO₃的稀微弧阳极氧化溶液中得到的阳极氧化膜的抗腐蚀性能。结果表明,在相同工艺条件下,在浓溶液中得到的氧化膜要比稀溶液配方中得到的氧化膜厚,并且耐腐蚀性能高,这表明本工艺的电流效率要高于稀溶液,更具有实用前途。更多还原

【Abstract】 A micro-arc oxidation process for AZ91, AZ31 and AM60 magnesium alloys based on an environmentally friendly alkaline electrolyte of 100 g·L^-1 NaOH + 20 g·L^-1 Na2B4O7?10H2O + 50 g·L^-1 C6H5Na3O7?2H2O + 60 g·L^-1 Na2SiO3?9H2O has been studied in this paper. The micro-arc oxidation process can form anodized film with good protective properties on magnesium alloys. At the same time, the electrochemical corrosion behaviors of different magnesium alloys and their anodized films were also studied. Finally, the micro-arc oxidation process in this study has been compared with a commonly-used micro-arc oxidation process in dilute solution.The micro-arc oxidation process was carried under constant current mode, different films were formed on AZ91, AZ31 and AM60 magnesium alloys by changing the processing parameters such as current density and processing time. The properties of the films were determined by electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization method. The investigation shows that when the applied current density is 20mA?cm-2 and the anodization time is 40min, the anti-corrosion properties of AZ91 and AZ31 magnesium alloys are best, while for AM60 magnesium alloy, when the applied current density is 20mA?cm-2 and the anodization time is 50min, its corrosion resistance has the optimum value. Microstructure and composition of films were examined by SEM, XRD and EDS. The micro-arc oxidation films are porous and their components consist of MgO and Mg2SiO4. The thicknesses of micro-arc oxidation films were measured by Coating Thickness Gauge and they increase linearly with time and current density respectively. Besides, the relationship between the corrosion resistance and the thickness was also studied and the result shows that there is an optimal thickness corresponding to the best corrosion resistance.The corrosion resistance of both the matrix of magnesium alloys and micro-arc oxidation samples were determined by neutral salt immersion test and EIS to study their corrosion mechanisms. The results show that the order of the corrosion resistance of the anodized films has the same order of the corrosion resistance of magnesium alloy matrix. The corrosion morphology of the matrix alloy is complete corrosion, while that of the anodized film is pitting, indicating the superior in corrosion resistance of the micro-arc oxidation coatings. Finally, the anodized films obtained in this study was compared to that based on a commonly-used dilute electrolyte of 5 g·L^-1 NaOH + 15 g·L^-1 Na₂SiO₃·9H₂O. The results show that the thickness and corrosion resistance of the micro-oxidation film in this study is higher than the films acquired in dilute solution, this indicate that the current efficiency in this process is higher than that in the dilute solution and thus more practical.更多还原