本文關(guān)鍵詞： 鎂合金 復(fù)合電解液 碳化硅顆粒/微弧氧化 特性　出處：《江蘇大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：本文采用微弧氧化技術(shù)(MAO)在恒流條件下在鎂合金表面制備陶瓷膜層,并以陶瓷膜層的耐蝕性做為主要評(píng)價(jià)指標(biāo),對(duì)鋁酸鈉-硅酸鈉復(fù)合電解液的組分、電源輸出參數(shù)、電源工作模式進(jìn)行了研究及優(yōu)化,確定最佳優(yōu)化參數(shù),并在此基礎(chǔ)上進(jìn)一步研究了納米碳化硅顆粒與微弧氧化技術(shù)復(fù)合膜層的制備工藝及特性。利用測(cè)厚儀、掃描電鏡、XRD、能譜儀、顯微硬度計(jì)研究了膜層厚度、顯微結(jié)構(gòu)形貌、相組成、膜層成分和硬度；利用摩擦磨損儀測(cè)試了膜層的耐磨性；在3.5%NaCl中性溶液中采用靜態(tài)失重試驗(yàn)、極化曲線、電化學(xué)阻抗譜(EIS)等方法測(cè)試膜層的耐蝕性能。結(jié)果表明：在鋁酸鈉-硅酸鈉復(fù)合電解液中,鎂合金微弧氧化膜層厚度及耐蝕性隨著組分鋁酸鈉、硅酸鈉、四硼酸鈉、氫氧化鈉、檸檬酸鈉、丙三醇濃度的增加呈現(xiàn)出先提高后降低的變化趨勢(shì)。鋁酸鈉、四硼酸鈉為膜層耐蝕性的主要影響因素,鋁酸鈉、硅酸鈉、四硼酸鈉和丙三醇為膜層厚度的主要影響因素。經(jīng)優(yōu)化確定：鋁酸鈉9 g/L、硅酸鈉15 g/L、四硼酸鈉2g/L、氫氧化鈉3g/L、檸檬酸鈉7g/L、丙三醇5 mL/L為綠色復(fù)合電解液組元最佳配方。不同的電源輸出參數(shù)下,膜層的耐蝕性隨著電流密度、脈沖頻率、占空比及氧化時(shí)間增加先提高后降低的變化趨勢(shì),膜層厚度的變化趨勢(shì)與耐蝕性有所不同。電流密度是膜層耐蝕性的主要影響因素,電流密度、氧化時(shí)間是膜層厚度主要影響因素。利用正交優(yōu)化試驗(yàn)確定電流密度15 A/dm2、脈沖頻率520Hz、正占空比38%及氧化時(shí)間15min為本體系中最佳電源輸出參數(shù)。不同電源工作模式下,與單極性相比,雙極性下膜層致密,均勻,具有更好的耐腐蝕性能,確定本體系采用雙極性電源工作模式。復(fù)合膜層耐蝕性隨著碳化硅濃度的增加先提高后降低,膜層的厚度隨著碳化硅濃度的增加而增加,當(dāng)碳化硅濃度為4g/L時(shí)復(fù)合膜層致密,均勻,耐蝕性最佳。鎂合金微弧氧化過程可分為活性溶解、活化鈍化、鈍化、過鈍化四個(gè)區(qū)。在恒流氧化模式下,該體系中微弧氧化膜層生長(zhǎng)過程可分為陽極氧化膜形成期、微弧氧化膜快速生長(zhǎng)期,微弧氧化膜局部生長(zhǎng)期三個(gè)階段。單一膜層主要由O元素、Mg元素、Al元素、Si元素組成,并且氧化時(shí)間不同,各元素的含量不同。復(fù)合膜層由于碳化硅的加入膜層中比單一膜層增加了C元素,C元素隨著碳化硅濃度的增加而增加,其在膜層分布規(guī)律是外層分布稍高,內(nèi)部較低,但總體含量較少。在不同的工藝條件下微弧氧化陶瓷膜層均由MgO、MgAl2O4、Mg2SiO4三相組成,但工藝條件影響它們的濃度比例的分配。微弧氧化可有效地提高鎂合金的耐蝕性和耐磨性,單一膜層與基體相比,自腐蝕電極電位提高150mV,腐蝕電流密度降低3個(gè)數(shù)量級(jí),磨損率性下降20%。碳化硅顆粒與微弧氧化復(fù)合膜層的耐蝕性、耐磨性可進(jìn)一步提高,但耐磨性提高的更加顯著；復(fù)合膜層的綜合質(zhì)量?jī)?yōu)于單一膜層。
[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.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG174.4

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