發(fā)布時間：2018-07-23 17:48

【摘要】：鎂合金耐蝕性能較差,嚴重阻礙了工程領域中的應用,因而改善鎂合金表面耐腐性能成為社會亟待解決的問題。本論文采用電化學輔助沉積和微弧氧化技術(shù)在ZK60鎂合金表面原位構(gòu)筑耐蝕膜層,為ZK60鎂合金在工程領域中的應用奠定基礎。論文利用電化學輔助沉積技術(shù),在十六烷基三甲氧基硅烷(HTMS)/正硅酸乙酯體系中,分別探討了沉積電位、沉積時間和添加劑十六烷基三甲基溴化銨(CTAB)對SiO_2硅烷薄膜厚度、疏水性和耐蝕性能的影響。實驗結(jié)果表明,增加沉積電位和沉積時間,可顯著增加SiO_2硅烷薄膜厚度,降低鎂合金基體腐蝕電流密度。添加劑CTAB能夠增強SiO_2硅烷薄膜疏水性能,顯著縮短膜層達到超疏水狀態(tài)的沉積時間。利用分子動力學和量子化學的方法分析了HTMS在鎂合金表面成膜機理。分子動力學模擬結(jié)果表明,HTMS在鎂合金表面能夠形成吸附,其吸附能為-76.03 kcal/mol。密度泛函理論計算結(jié)果表明:HTMS分子的HOMO軌道與金屬的空軌道形成成鍵軌道;其LUMO軌道易得到金屬的電子形成反鍵軌道,成鍵與反鍵之間的協(xié)同作用實現(xiàn)HTMS分子吸附;分子前線軌道理論Fukui指數(shù)表明HTMS分子吸附活性位點為硅羥基。為解決電化學輔助沉積過程中存在膜層結(jié)合力較差,對鎂合金形狀具有依賴性的難題。實驗中以Na_2SiO_3-KOH-NaF為電解液體系,采用微弧氧化技術(shù)在ZK60鎂合金表面原位構(gòu)筑陶瓷膜層,以增加鎂合金器件在工程領域的應用。首先,通過正交實驗法優(yōu)化電解液中各組分濃度,確定最佳電解液體系。分別研究了電流密度、頻率、占空比和反應時間對微弧氧化膜層耐蝕性能的影響,確定最佳工藝參數(shù)。通過測試陶瓷膜層的形貌可知:陶瓷膜層表面含有大量的微孔及裂痕。由XRD和XPS分析可知,陶瓷膜層主要以Mg_2SiO_4相、MgO相及未完全反應的金屬Mg相組成。耐蝕性能結(jié)果表明:微弧氧化技術(shù)能夠顯著提高鎂合金的耐蝕性能;其中,陶瓷膜層腐蝕電位比基體提高0.25 V,腐蝕電流密度降低至7.60×10~(-8)A/cm~2。為實現(xiàn)不同形狀鎂合金連接件表面及螺紋強化處理,研究了丙三醇分子對微弧氧化反應過程影響。實驗結(jié)果表明,丙三醇分子的存在能夠促進微弧氧化反應的進行,降低氧氣氣泡體積;并且能夠有效解決反應過程中因電場分布不均而產(chǎn)生的局部放電現(xiàn)象。丙三醇添加濃度對陶瓷膜層微觀形貌、元素組成、相組成及耐蝕性能有重要影響。當添加濃度濃度為100 m L/L時,陶瓷膜層具有較少的表面缺陷和較高的耐腐蝕性能,其腐蝕電流密度為4.30×10~(-8)A/cm~2,比基體耐蝕性能提高近萬倍。此外,丙三醇的添加能夠顯著改善連接件邊緣及盲孔螺紋表面膜層質(zhì)量。實驗利用分子動力學的方法分析了丙三醇對微弧氧化過程及膜層生長的影響。結(jié)果表明,丙三醇分子在鎂合金表面能夠形成強烈的吸附,改變?nèi)芤?基體界面的組成和性質(zhì),分割反應位點使得膜層表面放電均勻,降低放電斑點尺寸,在反應過程中起到“柔化”放電的作用。為改善微弧氧化陶瓷膜層表面質(zhì)量,進一步提高陶瓷膜層的耐蝕性能,對陶瓷膜層進行表面改性研究。首先,在微弧氧化陶瓷膜層表面,實驗分別研究磁場條件對四氧化三鐵/HTMS復合薄膜構(gòu)筑的影響。結(jié)果表明:在磁場誘導作用下,四氧化三鐵呈陣列結(jié)構(gòu),其疏水角為157°,實現(xiàn)超疏水復合膜層的制備。耐蝕性能表明,超疏水復合薄膜的腐蝕電流密度比基體降低4個數(shù)量級,僅為1.44×10~(-8)A/cm~2,顯著提高鎂合金基體的耐蝕性能;其次,利用改性Hummer法成功制備了氧化石墨烯,并利用氧化石墨烯表面具有含氧官能團的特性,將氧化石墨烯溶液填充陶瓷表面微孔與裂痕處,原位組裝形成化學穩(wěn)定、耐蝕性較強氧化石墨烯薄膜。通過測試微弧氧化/氧化石墨烯復合薄膜耐蝕性能可知,微弧氧化/氧化石墨烯復合膜層在3.5 wt%Na Cl溶液體系浸泡100 h不發(fā)生腐蝕,其腐蝕電流密度降低至1.45′10~(-8) A/cm~2,比微弧氧化陶瓷膜層耐蝕性能提高5倍,實現(xiàn)進一步提高鎂合金耐腐蝕性能。
[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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG178

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本文編號：2140165