复合电解液中镁合金微弧氧化复合膜层制备及特性研究

发布时间：2018-02-13 18:35

本文关键词： 镁合金复合电解液碳化硅颗粒/微弧氧化特性　出处：《江苏大学》2015年博士论文　论文类型：学位论文

【摘要】：本文采用微弧氧化技术(MAO)在恒流条件下在镁合金表面制备陶瓷膜层,并以陶瓷膜层的耐蚀性做为主要评价指标,对铝酸钠-硅酸钠复合电解液的组分、电源输出参数、电源工作模式进行了研究及优化,确定最佳优化参数,并在此基础上进一步研究了纳米碳化硅颗粒与微弧氧化技术复合膜层的制备工艺及特性。利用测厚仪、扫描电镜、XRD、能谱仪、显微硬度计研究了膜层厚度、显微结构形貌、相组成、膜层成分和硬度；利用摩擦磨损仪测试了膜层的耐磨性；在3.5%NaCl中性溶液中采用静态失重试验、极化曲线、电化学阻抗谱(EIS)等方法测试膜层的耐蚀性能。结果表明：在铝酸钠-硅酸钠复合电解液中,镁合金微弧氧化膜层厚度及耐蚀性随着组分铝酸钠、硅酸钠、四硼酸钠、氢氧化钠、柠檬酸钠、丙三醇浓度的增加呈现出先提高后降低的变化趋势。铝酸钠、四硼酸钠为膜层耐蚀性的主要影响因素,铝酸钠、硅酸钠、四硼酸钠和丙三醇为膜层厚度的主要影响因素。经优化确定：铝酸钠9 g/L、硅酸钠15 g/L、四硼酸钠2g/L、氢氧化钠3g/L、柠檬酸钠7g/L、丙三醇5 mL/L为绿色复合电解液组元最佳配方。不同的电源输出参数下,膜层的耐蚀性随着电流密度、脉冲频率、占空比及氧化时间增加先提高后降低的变化趋势,膜层厚度的变化趋势与耐蚀性有所不同。电流密度是膜层耐蚀性的主要影响因素,电流密度、氧化时间是膜层厚度主要影响因素。利用正交优化试验确定电流密度15 A/dm2、脉冲频率520Hz、正占空比38%及氧化时间15min为本体系中最佳电源输出参数。不同电源工作模式下,与单极性相比,双极性下膜层致密,均匀,具有更好的耐腐蚀性能,确定本体系采用双极性电源工作模式。复合膜层耐蚀性随着碳化硅浓度的增加先提高后降低,膜层的厚度随着碳化硅浓度的增加而增加,当碳化硅浓度为4g/L时复合膜层致密,均匀,耐蚀性最佳。镁合金微弧氧化过程可分为活性溶解、活化钝化、钝化、过钝化四个区。在恒流氧化模式下,该体系中微弧氧化膜层生长过程可分为阳极氧化膜形成期、微弧氧化膜快速生长期,微弧氧化膜局部生长期三个阶段。单一膜层主要由O元素、Mg元素、Al元素、Si元素组成,并且氧化时间不同,各元素的含量不同。复合膜层由于碳化硅的加入膜层中比单一膜层增加了C元素,C元素随着碳化硅浓度的增加而增加,其在膜层分布规律是外层分布稍高,内部较低,但总体含量较少。在不同的工艺条件下微弧氧化陶瓷膜层均由MgO、MgAl2O4、Mg2SiO4三相组成,但工艺条件影响它们的浓度比例的分配。微弧氧化可有效地提高镁合金的耐蚀性和耐磨性,单一膜层与基体相比,自腐蚀电极电位提高150mV,腐蚀电流密度降低3个数量级,磨损率性下降20%。碳化硅颗粒与微弧氧化复合膜层的耐蚀性、耐磨性可进一步提高,但耐磨性提高的更加显著；复合膜层的综合质量优于单一膜层。
[Abstract]:In this paper, ceramic coatings were prepared on the surface of magnesium alloys under constant current conditions by means of micro-arc oxidation (Mao). The corrosion resistance of ceramic coatings was used as the main evaluation index. The composition of sodium aluminate / sodium silicate composite electrolyte and the output parameters of power supply were studied. The working mode of power supply is studied and optimized, and the optimum parameters are determined. On the basis of this, the preparation process and characteristics of composite film layer of nano-silicon carbide particles and micro-arc oxidation technology are further studied. The thickness, microstructure, phase composition, composition and hardness of the film were studied by scanning electron microscopy (SEM) XRD, energy spectrometer and microhardness tester. The wear resistance of the film was tested by friction and wear tester, and the static weightlessness test was used in 3.5 NaCl neutral solution. Polarization curve, electrochemical impedance spectroscopy (EIS) and other methods were used to test the corrosion resistance of the film. The results showed that the thickness and corrosion resistance of magnesium alloy microarc oxide film were determined with the composition of sodium aluminate, sodium silicate and sodium tetraborate in the composite electrolyte of sodium aluminate and sodium silicate. The concentration of sodium hydroxide, sodium citrate and glycerol increased first and then decreased. Sodium aluminate and sodium tetraborate were the main factors affecting the corrosion resistance of the film, such as sodium aluminate, sodium silicate, sodium silicate, sodium aluminate, sodium silicate, sodium aluminate, sodium silicate, sodium silicate, sodium aluminate and sodium tetraborate. Sodium aluminate 9 g / L, sodium silicate 15 g / L, sodium tetraborate 2 g / L, sodium hydroxide 3 g / L, sodium citrate 7 g / L, propanetriol 5 mL/L were selected as green composite electrolyte components. Different power output parameters, With the increase of current density, pulse frequency, duty cycle and oxidation time, the corrosion resistance of the film increases first and then decreases. The change trend of the film thickness is different from that of the corrosion resistance, and the current density is the main factor affecting the corrosion resistance of the film. The current density and oxidation time are the main factors affecting the film thickness. The optimum power output parameters are determined by orthogonal optimization test: current density 15A / dm2, pulse frequency 520Hz, positive duty cycle 38% and oxidation time 15min. Compared with unipolarity, the film is compact, uniform, and has better corrosion resistance. It is determined that the working mode of bipolar power supply is adopted in this system. The corrosion resistance of the composite film increases first and then decreases with the increase of silicon carbide concentration. The thickness of the film increases with the increase of silicon carbide concentration. When the concentration of silicon carbide is 4 g / L, the composite film is compact, uniform and corrosion resistant. The process of micro-arc oxidation of magnesium alloy can be divided into active dissolution, activation passivation and passivation. In the constant current oxidation mode, the growth process of the micro-arc oxide film can be divided into anodic oxide film formation period, micro-arc oxide film rapid growth period. There are three phases in the local growth period of the micro-arc oxide film. The single layer is mainly composed of O element, mg element, Al element and Si element, and the oxidation time is different. The content of each element is different. Due to the addition of silicon carbide to the film layer, the C element and C element increase with the increase of the concentration of silicon carbide, and the distribution of C element in the film layer is slightly higher than that in the single film layer, and the distribution law is slightly higher in the outer layer and lower in the inner layer. But the total content is relatively small. The ceramic coatings of micro-arc oxidation are all composed of MgO- MgAl2O4- Mg2SiO4 under different technological conditions, but the technological conditions affect the distribution of their concentration ratio. Micro-arc oxidation can effectively improve the corrosion resistance and wear resistance of magnesium alloys. Compared with the substrate, the corrosion potential of the single film increases by 150 MV, the corrosion current density decreases by 3 orders of magnitude, the wear rate decreases by 20%. The corrosion resistance and wear resistance of silicon carbide particle and micro-arc oxidation composite film can be further improved. However, the wear resistance of the composite film is better than that of the single film.
【学位授予单位】：江苏大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG174.4

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