ZK60镁合金表面原位构筑耐腐蚀膜层及性能研究

发布时间：2018-07-23 17:48

【摘要】：镁合金耐蚀性能较差,严重阻碍了工程领域中的应用,因而改善镁合金表面耐腐性能成为社会亟待解决的问题。本论文采用电化学辅助沉积和微弧氧化技术在ZK60镁合金表面原位构筑耐蚀膜层,为ZK60镁合金在工程领域中的应用奠定基础。论文利用电化学辅助沉积技术,在十六烷基三甲氧基硅烷(HTMS)/正硅酸乙酯体系中,分别探讨了沉积电位、沉积时间和添加剂十六烷基三甲基溴化铵(CTAB)对SiO_2硅烷薄膜厚度、疏水性和耐蚀性能的影响。实验结果表明,增加沉积电位和沉积时间,可显著增加SiO_2硅烷薄膜厚度,降低镁合金基体腐蚀电流密度。添加剂CTAB能够增强SiO_2硅烷薄膜疏水性能,显著缩短膜层达到超疏水状态的沉积时间。利用分子动力学和量子化学的方法分析了HTMS在镁合金表面成膜机理。分子动力学模拟结果表明,HTMS在镁合金表面能够形成吸附,其吸附能为-76.03 kcal/mol。密度泛函理论计算结果表明:HTMS分子的HOMO轨道与金属的空轨道形成成键轨道;其LUMO轨道易得到金属的电子形成反键轨道,成键与反键之间的协同作用实现HTMS分子吸附;分子前线轨道理论Fukui指数表明HTMS分子吸附活性位点为硅羟基。为解决电化学辅助沉积过程中存在膜层结合力较差,对镁合金形状具有依赖性的难题。实验中以Na_2SiO_3-KOH-NaF为电解液体系,采用微弧氧化技术在ZK60镁合金表面原位构筑陶瓷膜层,以增加镁合金器件在工程领域的应用。首先,通过正交实验法优化电解液中各组分浓度,确定最佳电解液体系。分别研究了电流密度、频率、占空比和反应时间对微弧氧化膜层耐蚀性能的影响,确定最佳工艺参数。通过测试陶瓷膜层的形貌可知:陶瓷膜层表面含有大量的微孔及裂痕。由XRD和XPS分析可知,陶瓷膜层主要以Mg_2SiO_4相、MgO相及未完全反应的金属Mg相组成。耐蚀性能结果表明:微弧氧化技术能够显著提高镁合金的耐蚀性能;其中,陶瓷膜层腐蚀电位比基体提高0.25 V,腐蚀电流密度降低至7.60×10~(-8)A/cm~2。为实现不同形状镁合金连接件表面及螺纹强化处理,研究了丙三醇分子对微弧氧化反应过程影响。实验结果表明,丙三醇分子的存在能够促进微弧氧化反应的进行,降低氧气气泡体积;并且能够有效解决反应过程中因电场分布不均而产生的局部放电现象。丙三醇添加浓度对陶瓷膜层微观形貌、元素组成、相组成及耐蚀性能有重要影响。当添加浓度浓度为100 m L/L时,陶瓷膜层具有较少的表面缺陷和较高的耐腐蚀性能,其腐蚀电流密度为4.30×10~(-8)A/cm~2,比基体耐蚀性能提高近万倍。此外,丙三醇的添加能够显著改善连接件边缘及盲孔螺纹表面膜层质量。实验利用分子动力学的方法分析了丙三醇对微弧氧化过程及膜层生长的影响。结果表明,丙三醇分子在镁合金表面能够形成强烈的吸附,改变溶液/基体界面的组成和性质,分割反应位点使得膜层表面放电均匀,降低放电斑点尺寸,在反应过程中起到“柔化”放电的作用。为改善微弧氧化陶瓷膜层表面质量,进一步提高陶瓷膜层的耐蚀性能,对陶瓷膜层进行表面改性研究。首先,在微弧氧化陶瓷膜层表面,实验分别研究磁场条件对四氧化三铁/HTMS复合薄膜构筑的影响。结果表明:在磁场诱导作用下,四氧化三铁呈阵列结构,其疏水角为157°,实现超疏水复合膜层的制备。耐蚀性能表明,超疏水复合薄膜的腐蚀电流密度比基体降低4个数量级,仅为1.44×10~(-8)A/cm~2,显著提高镁合金基体的耐蚀性能;其次,利用改性Hummer法成功制备了氧化石墨烯,并利用氧化石墨烯表面具有含氧官能团的特性,将氧化石墨烯溶液填充陶瓷表面微孔与裂痕处,原位组装形成化学稳定、耐蚀性较强氧化石墨烯薄膜。通过测试微弧氧化/氧化石墨烯复合薄膜耐蚀性能可知,微弧氧化/氧化石墨烯复合膜层在3.5 wt%Na Cl溶液体系浸泡100 h不发生腐蚀,其腐蚀电流密度降低至1.45′10~(-8) A/cm~2,比微弧氧化陶瓷膜层耐蚀性能提高5倍,实现进一步提高镁合金耐腐蚀性能。
[Abstract]:The corrosion resistance of magnesium alloys is poor, which seriously hinders the application in the field of engineering. Therefore, it is an urgent problem to improve the corrosion resistance of magnesium alloys on the surface of magnesium alloys. This paper uses electrochemical assisted deposition and micro arc oxidation technology to construct the corrosion resistance film in situ on the surface of ZK60 magnesium alloy, laying the foundation for the application of ZK60 magnesium alloy in the field of engineering. The effects of deposition potential, deposition time and additive sixteen alkyl three methyl ammonium bromide (CTAB) on the thickness, hydrophobicity and corrosion resistance of SiO_2 silane film were investigated by electrochemical assisted deposition in the sixteen alkyl trimethoxy silane (HTMS) / tetraethyl orthosilicate system. The experimental results showed that the deposition potential was increased. The deposition time can significantly increase the thickness of SiO_2 silane film and reduce the corrosion current density of the magnesium alloy matrix. The additive CTAB can enhance the hydrophobicity of SiO_2 silane film and significantly shorten the deposition time of the film to the superhydrophobic state. Molecular dynamics and quantum chemistry have been used to analyze the mechanism of HTMS film formation on the surface of magnesium alloy. The dynamic simulation results show that HTMS can form adsorption on the surface of magnesium alloy, and its adsorption energy is -76.03 kcal/mol. density functional theory calculation results show that the HOMO orbit of HTMS molecule forms bond orbit with the hollow orbit of metal; its LUMO orbit is easy to get the anti bond orbit of metal electrons and the coordination between bonding and anti bonding to realize H TMS molecular adsorption and molecular front-line orbital theory Fukui index indicate that the adsorption site of HTMS molecules is silicon hydroxyl. In order to solve the problem of dependence on the shape of the magnesium alloy in the process of electrochemical auxiliary deposition, the presence of the membrane of the magnesium alloy is poor. In the experiment, Na_2SiO_3-KOH-NaF is used as the electrolyte system and the microarc oxidation technology is used in the ZK60 magnesium alloy table. The ceramic coating is constructed in situ to increase the application of magnesium alloy devices in the engineering field. First, the optimum electrolyte system is determined by orthogonal experimental method. The effect of current density, frequency, duty ratio and reaction time on corrosion resistance of micro arc oxide film layer is studied, and the best process parameters are determined. The surface morphology of the ceramic coating shows that the surface of the ceramic coating contains a lot of micropores and cracks. By XRD and XPS analysis, the ceramic coating is mainly composed of Mg_2SiO_4 phase, MgO phase and the incomplete reaction metal Mg phase. The corrosion resistance results show that the corrosion resistance of the magnesium alloy can be greatly improved by the micro arc oxidation technology. The corrosion potential is increased by 0.25 V, and the corrosion current density is reduced to 7.60 x 10~ (-8) A/cm~2. to enhance the surface and thread intensification of different shapes of magnesium alloy joints. The effect of the molecules of glycerol on the micro arc oxidation process is studied. The experimental results show that the deposit of glycerol molecule can promote the oxidation reaction of micro arc and reduce the oxygen. The volume of the bubble and the partial discharge caused by the uneven distribution of the electric field can be effectively solved. The addition concentration of glycerol has an important effect on the microstructure, composition, phase composition and corrosion resistance of the ceramic coating. When the concentration is 100 m L/L, the ceramic coating has less surface defects and higher resistance. The corrosion current density is 4.30 x 10~ (-8) A/cm~2, and the corrosion resistance of the base body is increased by nearly 10000 times. In addition, the addition of glycerol can significantly improve the quality of the surface film layer on the edge of the joint and the blind hole thread surface. The molecules of glycerol can form a strong adsorption on the surface of magnesium alloy, change the composition and properties of the interface of the solution / matrix, divide the reaction site to make the surface of the film evenly discharge, reduce the size of the discharge spots, and play the role of "softening" the discharge during the reaction process. The corrosion resistance of the coating is studied on the surface modification of the ceramic coating. First, the effect of magnetic field conditions on the structure of the /HTMS composite film of iron oxide is studied on the surface of micro arc oxidation ceramic coating. The results show that, under the induction of magnetic field, iron oxide has array structure and its hydrophobic angle is 157 degrees, and the superhydrophobic composite film is realized. The corrosion resistance shows that the corrosion current density of the superhydrophobic composite film is reduced by 4 orders of magnitude, only 1.44 x 10~ (-8) A/cm~2, which significantly improves the corrosion resistance of the magnesium alloy matrix. Secondly, the modified Hummer method is used to prepare graphene oxide successfully, and the properties of oxygen containing functional groups on the surface of graphene oxide are obtained. The solution filled with micropores and cracks on the ceramic surface was assembled in situ to form chemically stable and corrosion-resistant graphene oxide films. By testing the corrosion resistance of microarc oxidation / graphene oxide composite films, microarc oxidation / graphene oxide composite films were soaked in 3.5 wt%Na Cl solution system for 100 h without corrosion. The current density is reduced to 1.45 '10~ (-8) A/cm~2, which is 5 times higher than that of the micro arc oxidation ceramic coating, which can further improve the corrosion resistance of magnesium alloy.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG178

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