【作者】 李康；

【导师】 徐用军；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2008， 硕士

【摘要】 本课题针对镁锂合金耐腐蚀性差的问题,在Na2SiO3、Na3PO4及Na2SiO3-Na3PO4三种电解液体系下,利用微弧氧化技术在Mg-5mass%Li合金板材表面原位生长耐蚀陶瓷膜层,通过电解液配方的确定,工艺参数的优化以及添加剂的掺杂,系统地分析了各种因素对膜层结构与性能的影响规律。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、电子能谱仪(EDS)等测试手段,分析膜层的物相及元素组成,观察陶瓷膜层表面及截面形貌;利用电涡流测厚仪测试膜层厚度;利用CHI604电化学测试仪、腐蚀失重试验研究陶瓷膜的耐腐蚀性能。Na2SiO3电解液体系优化工艺条件下制备的陶瓷膜层厚度约20μm,主晶相为MgO、Mg2SiO4,表面均匀平整,陶瓷膜耐点腐蚀性能最好,盐水浸泡过程中腐蚀速率较低,耐盐水腐蚀性能较好。Na3PO4电解液体系优化工艺条件下制备的陶瓷膜厚约40μm,主晶相为MgO、MgF2,表面不均匀、存在龟裂,陶瓷膜耐蚀性能最差。Na2SiO3-Na3PO4电解液体系优化工艺条件下制备的陶瓷膜厚约15μm,主晶相为MgO、MgSiO3,膜层均匀致密且孔径小,其耐均匀腐蚀和盐水腐蚀性能最好。添加剂掺杂能够有效的改善膜层的结构和性能,EDTA掺杂降低电解液氧化成膜的能力,陶瓷膜层厚度变小、孔径减小,耐均匀腐蚀性能提高。Na2B4O7掺杂增强了电解液的氧化成膜能力,陶瓷膜层厚度和致密度增强,耐点蚀性能提高。陶瓷膜层元素能谱分析表明,陶瓷膜从内层到外层,F元素含量明显减少,Si和P元素逐渐增多,因此,Mg-Li合金在Na2SiO3-Na3PO4电解液体系的成膜过程中,反应初期以F优先参与成膜为主,随着反应进行更多的Si和P参与成膜反应。更多还原

【Abstract】 In this paper, in order to improve the poor corrosion resistance property of Mg-Li alloy, ceramic coatings were formed on Mg-5mass%Li substrate by micro-arc oxidation in Na2SiO3, Na3PO4 and Na2SiO3-Na3PO4 solution system respectively. Effect of factors (electrolyte system, processing parameters and additive) on the structure and corrosion resistance property of ceramic coatings were studied.X-ray diffraction(XRD) and electronic differential system(EDS) were applied for detection of the phase and elemental composition of ceramic coatings. Scanning electron microscopy(SEM) and numeral camera were employed for observation of the surface morphologies. Ectric eddy current thickness tester had been used to caculate the thicknesses of the ceramic coatings. The corrosion resistance of the ceramic coatings had been evaluated by CHI604 electrical equipment and weight loss measurements.The coating prepared in Na2SiO3 solution system was approximate 20μm and mainly composed of MgO and Mg2SiO4. The coating had the best pitting corrosion resistance and lower salty water corrosion rate in term of cyclic voltammetry curves and weight loss measurements. The coatings prepared in Na3PO4 solution system were about 40μm and the main crystal phases were MgO and MgF2. Nonuniform micro-structure and the checked surface of the coating resulted in lower corrosion resistance property. The coatings prepared in Na2SiO3-Na3PO4 solution system were about 15μm and composed of MgO and MgSiO3, The coating was uniform and compact, so it had the best general corrosion resistance and salty water corrosion resistance in term of Tafel polarization curves and weight loss measurements.Additive could improve structure and properties of coatings, small quantity of EDTA was added in the solution made coatings more thinner and uniform which resulted in the improvement of general corrosion resistance. The addition of Na2B4O7 in the solution made coatings thicker and compacter, which made for the improvement of the pitting corrosion resistance. The EDS analysis of the ceramic coatings showed that the content of element F decreased obviously but the content of Si and P increased gradually from the inner layer to top layer, which meaned the element F took precedence of S and P to participate in the formation of the ceramic coating during the initial stage. More content of Si and P participated in the formation of the coating gradually with the growth of the ceramic coating.更多还原