臺灣博碩士論文加值系統

本研究主要探討微弧氧化技術中，電源供給之正負電荷量對整體製程與含鋯鎂金屬基材之膜層影響，特別針對膜層中鋯元素含量變化與相分佈位置加以觀察，以SEM、EDS與XRD做膜層微觀形貌、元素含量與相結構分析，並搭配製程中電壓與脈衝變化作參考依據，最後使用酸、中與鹼性氯化鈉溶液對不同鋯成份分佈與緻密膜層做浸泡測試，評估其於不同酸鹼環境中之抗蝕能力。
於第一部份鍍製不同鋁元素含量之鎂基材發現，鋁與基底鎂析出之Mg17Al12(β相)對初始成膜具有相當重要影響，歸因於顯微結構中α相與β相氧化程度不同，造成電荷無法均勻累積產生穩定電弧。而電解液中若提升氟離子濃度，有助於初始氧化膜生成，使受到兩相氧化程度影響之基材擁有穩定成膜品質。另外電解液中若含有微量沉澱，細微顆粒會以電泳方式移動至電極沉積，膜層因此具有緻密化效果。
第二部份由不同電荷比實驗得知，單位時間內負電荷多寡明顯影響膜層緻密性、生長方向與相成份分佈，當供給之負電荷小於等於正電荷時，陽極之正能量充足，因此試片表面擁有穩定電弧；而當負電荷大於正電荷時，正電壓具有異常降低情形，工作能量受限情況下，試片表面僅能產生局部靜態弧光使膜層品質降低。負電荷量增加有助於吸引電解液中之正離子於試片表面，膜層表面之鋯含量因此具有影響，而負電荷也同時影響相成份分佈，膜層外部主要為含鋯相t-ZrO2、c-ZrO2與Mg2Zr5O12；而靠近基材內層則為氧向基材擴散所生成之氧化鎂，氧擴散程度與負電荷量成正比，對應氧化鎂厚度與膜層內外生長趨勢，向內生長機制膜厚與氧擴散程度有關。
最後經過不同酸鹼值浸泡得知，膜層於酸性環境氯離子攻擊情形最為嚴重，而鹼性環境中鎂之腐蝕產物於可穩定存在，因此於鹼性環境中腐蝕情形最輕微。腐蝕抵抗能力與緻密性以及相成份分佈有關，在兩種相分佈型態膜層試片中，內部具緻密氧化鎂相，較含孔洞之鋯相膜層耐蝕性佳，而擁有高負電荷所吸引之鋯元素於膜層表面，可大幅延長腐蝕攻擊時間，因此電荷比1.5/1.5之膜層具有較佳耐蝕特性。

In this study, the characteristics of the zirconia coating on magnesium alloys were discussed on different charge ratio using micro-arc discharge oxidation (MDO) process in zirconate-based electrolyte. The element content and phase distribution of zirconia coating from charge ratio plasma have been investigated. The morphologies and phase components of the coating were examined by SEM and XRD. In order to understand the corrosion behavior of the zirconia coatings with different phase composition distribution, the zirconia coatings were immersed in chloride environments with varying pH value.
In the first part, it was found that the content of aluminum in the Mg17Al12 (β-phase) magnesium alloys substrate precipitation has a very important effect during the initial deposition process. The formation of an initial oxide film in the early stage is caused by Mg matrix (α-phase) and Mg17Al12 (β-phase) which have different oxidation potential. Therefore, the electric charge can’t reach the breakdown potential. The addition of the fluoride ion concentration can help the initial oxide film formation. As a result, the β-phase substrate can emit arc. If the electrolytes have partial precipitation, the particles can help the film densification using electrophoretic adsorption.
The second part of the experiment discusses about the effect of positive and negative charge ratio. There is some evidence that negative charge significantly affects coatings density, growth direction, and phase distribution of zirconia coatings. Increasing the negative charge can help cation adsorption to anode electrode which can produce high zirconia content on the coating surface. Simultaneously, the negative charge can affect the phase distribution of the zirconia coatings. The cross-sectional morphologies of charge ratio coating BEI image have different type layer. The coating is relatively dense and composed of MgO in the inner layer and ZrO2- Mg2Zr5O12-MgO in the outer layer. With the increase in negative charge, the thickness of the MgO inner layer starts evolving. Inner layer thickness is related to the degree of oxygen diffusion. And the degree of oxygen diffusion is related to charge ratio.
The final part of this research discusses about the two types of zirconia coating component immersed in NaCl solution with pH of 3, 7 and 11, respectively. The experiment results show that rapid chemical dissolution happened in the oxide coating and lost its protection capability very quickly in acidic NaCl solution. In the alkaline NaCl solution, the coating underwent only a slight degradation. On the other hand, the results show that the deterioration of MDO coating was influenced by its density and composition distribution. It can be found that the coatings formed in small charge ratio have dense inner layer and mainly composed of MgO which can provide good corrosion protection for a long period of time. The coating produced in large charge ratio was mainly composed of zirconia, but pores in the coating suffered from rapid chemical dissolution.

中文摘要 I
Abstract III
目錄 V
圖目錄 VIII
表目錄 XII
第一章 前言 1
第二章 文獻回顧 3
2.1 鎂及其合金簡介 3
2.1.1 鎂及其合金發展與物理特性 3
2.1.2 鎂合金的表示方式 4
2.1.3 合金元素對鎂合金性質影響 6
2.1.4 鎂及其合金的化學特性與腐蝕行為 7
2.1.5 鎂及其合金表面防蝕處理 12
2.2 微弧氧化技術簡介 14
2.2.1 微弧氧化技術發展 14
2.2.2 微弧放電工作原理 14
2.2.3 影響膜層特性之控制因子 17
2.3 微弧氧化鍍製含鋯氧化膜 26
2.3.1 氧化鋯簡介 26
2.3.2 Mg2Zr5O12簡介 28
2.3.3 含鋯膜層鍍法 29
第三章 實驗方法 33
3.1 實驗藥品與設備規格 33
3.1.1 實驗藥品規格 33
3.1.2 實驗設備 33
3.2 實驗流程 35
3.3 試片製備 35
3.4 參數設定 36
3.4.1 第一部份實驗-基材與電解液之選擇 36
3.4.2 第二部份實驗-電荷比對膜層影響 38
3.4.3 第三部份實驗-不同酸鹼環境浸泡測試 39
3.5 儀器原理及實驗分析 39
3.5.1 掃描式電子顯微鏡 40
3.5.2 X-ray繞射儀 41
3.5.3 膜厚測定儀 41
3.5.4 維克氏硬度機 42
3.5.5 恆電位儀與交流阻抗分析儀 43
第四章 結果與討論 45
4.1 第一部分實驗-基材與電解液之選擇 45
4.1.1 不同鋁含量基材與添加NaF電解液對膜層成長之影響 46
4.1.2 不同鋁含量基材與添加NaF電解液對膜層微觀結構影響 50
4.1.3 不同鋁含量基材與膜層成份結構關係 55
4.2 第二部分實驗-電荷比對膜層影響 56
4.2.1 不同CR值對電壓與脈衝影響 57
4.2.2 不同CR值對膜層微觀結構影響 61
4.2.3 不同CR值對膜層成份結構影響 67
4.2.4 不同CR值膜層之耐蝕表現 71
4.3 第三部分實驗-不同酸鹼環境浸泡測試 72
4.3.1 浸泡測試 73
4.3.2 浸泡測試後之微觀形貌 75
4.3.3 浸泡測試後之極化曲線分析 80
第五章 結論 83
參考文獻 85

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