【作者】 程琳；

【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， 2010， 硕士

【摘要】 对于镁锂合金,不同锂含量对应的合金晶相不同,所以合金中锂的含量对微弧氧化膜层成膜的影响有重要意义。针对此问题,利用微弧氧化技术,在Mg-5%Li合金、Mg-8%Li、Mg-11%Li合金和Mg-14%Li合金表面原位制备陶瓷膜层,对膜层的成膜过程进行了研究。利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、电子能谱仪（EDS）、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量膜层厚度;利用TR200粗糙度仪测量膜层粗糙度。利用电感耦合等离子体质谱（ICP-MS）观察成膜过程中锂元素的析出。在单组分硅酸盐体系下,通过电解液浓度范围的考察,确定了一组对四种基体均能稳定成膜的工艺,比较了该工艺下四种基体成膜过程中随氧化时间的增加,电压、膜层厚度、膜层粗糙度以及膜层中的相组成、基体晶相组织、溶液中Li⁺浓度的变化规律。研究表明,四种基体微弧氧化过程基本一致。随着锂含量的增加,微弧氧化过程中电压值下降。陶瓷膜层元素涵盖电解液及基体的主要成分,其中MgO和Mg₂SiO₄为主晶相;四种合金膜层中Mg₂SiO₄的生成时间相对为:α相+β相>β相>α相。在微弧氧化过程中四种基体均有Li+的析出,析出含量次序位14%>11%≈8%>5%。说明不同锂含量的镁锂合金,锂含量越多,微弧氧化过程中析出的锂越多。并且11%Li、14%Li在微弧氧化过程中基体表层与膜层接界处发生基体晶相的转变,即有β相（Li₃Mg₇）→α相（Li0.92Mg₄.08）晶相转变过程发生。另外,不同的添加剂对膜层的生长影响的方式不同。本实验所采用的添加剂分别为NaOH和NaF,二者均可增加溶液电导率、对膜层有溶解作用,并且对成膜过程物质生成反应影响小。但影响主晶相MgO和Mg₂SiO₄的生成时间,添加剂NaF使得主晶相生成时间最慢。另外,在本实验中,NaOH在低浓度时主要作用为促进膜层的生长,高浓度时主要作用为对膜层的溶解;而F-在基体表面的富集,抑制了膜层的溶解,从而促进了膜层的生长。更多还原

【Abstract】 For the Mg-Li alloy, different phase correspond to different content of Li in the alloys. Therefore, the content of Li do a important part for the film coating in the oxidation process. As far as this problem is concerned, the technique of MAO was used for the preperation of coatings on Mg-5% Li alloy, Mg-8% Li, Mg-11% Li and Mg-14% Li alloys. With regard to the result, the mechanism of the MAO coating formation was studied.X-ray diffraction （XRD）, Energy dispersive X-ray spectroscopy （EDS） were applied for analyze the phase and elemental composition of the ceramic coatings. Scanning electron microscopy （SEM） was employed to observe the surface and section morphology. Ectric eddy current thickness gauge was used to calculate the thicknesses of the ceramic coatings. TR200 roughness was used to calculate film roughness. In addition, inductively coupled plasma mass spectrometry （ICP-MS） was applied to confirm the precipitation of lithium in the process of coating formation.Growth process of the ceramic coatings on four kinds of alloy were studied in a single system and the influential factors such as Voltage curve, coating thickness, coating roughness,surface morphology, surface elements, and the changes of Li+ concentration in solution. The probable formulas of MAO process on alloy with various Li content were deduced, and the effect of Li on formation of MAO coating was concluded. The MAO voltage would be drop as the content of Li increased in the alloy. The films were mainly consisted of MgO and Mg2SiO4 crystallized phases, but the growth time of Mg2SiO4 in the coating is different on the different alloys:α-phase +β-phase>β-phase>α-phase. Furthermore, the content of lithium ascended in the electrolyte throughout MAO reaction, and the precipitation of lithium: 14%>11%≈8%>5%. That notes there would be precipitated as more as the content of lithium increased in the alloy. Besides, there will be Li+ segregation in the surface of the alloy during the MAO process, and the crystal phase transition occurs:β-phase （Li₃Mg₇）→α-phase （Li0.92Mg₄.08）. In addition, different additives do a different part in the prcocess of films coatingin MAO. In this research, the additives are NaOH and NaF. Similarities of the two additives are that increasing the conductivity,dissoluting the coating and having little effect on the reaction process. However the two have different influence in the growth rate of crystallized phases such as MgO and Mg₂SiO₄. Specificly, the growth rate is lower in Na₂SiO₃+NaF electrolyte. In this experiment, the presence of OH- would be increasing the growth rate of coating at lower concentrations, but to contrary, the presence of OH- would be dissoluting the coating at higher concentration; F- would be inhibiting the dissolution to promote the growth of the film because of the F- enrichment in the surface of substrate.更多还原