- 學位論文
微弧氧化製程之電解液濃度與電參數對於AZ31鎂合金深色膜層性質之影響
Effect of Electrolyte Concentration and Electrical Parameters on Coating Properties of Dark Micro-Arc Oxidation on AZ31 Magnesium Alloy
摘要
鎂合金在輕量化的世代中擁有良好的發揮空間，但其耐磨耗性質不佳與抗蝕能力差是其應用上的缺點。透過微弧氧化的方式，能夠使鎂合金表面形成一層陶瓷氧化膜層，此膜層能夠提供鎂合金良好的耐磨耗性以及保護鎂合金基材減緩腐蝕的速率。 本研究透過調整微弧氧化製程當中氫氧化鈉、偏矽酸鈉、氟化鈉以及硫酸銅的濃度與使用不同的電流密度及工作頻率，在AZ31鎂合金上探討不同因子對膜層結構以及性質的影響。在分析方面利用掃描式電子顯微鏡、X光繞射儀以及X光光電子光譜儀了解膜層的結構以及成分；利用動電位極化曲線了解膜層的抗蝕能力，並透過分光色差儀量化膜層的外觀顏色數值。 研究結果指出，不同電解質上的濃度調整大多數均會影響膜層的結構以及成分，但經由微弧氧化製程後膜層均對鎂合金產生良好的保護性。影響膜層外層結構最明顯的電解質為氫氧化鈉，這是由於其影響電解液中導電度甚劇，使微弧氧化的放電程度有明顯的變化。影響膜層與基材間緻密層最多的電解質是氟化鈉，溶液中是否含有氟化鈉影響此層結構是否存在，也主導了膜層的抗腐蝕能力，但在過多的氟化鈉添加則會造成部分膜層的劣化情形。影響膜層外觀顏色最多的則是硫酸銅，且硫酸銅添加並不影響膜層中的其他性質。而電參數的控制以電流密度以及頻率為主，可以發現電流密度由於影響到提供微弧氧化進行的能量，與膜層厚度有很明顯的正相關；頻率雖然也影響厚度，但其效應不若電流密度來的明顯，其主要能改善膜層的結構，使膜層中的缺陷減少，並使膜層外觀的顏色更加均勻。
並列摘要
Magnesium alloys are widely applied in the lightweight field, but it faces two problems those are poor wear resistance and corrosion resistance. Magnesium alloys can be treated to generate ceramic-like oxide coatings on its surface with micro-arc oxidation (MAO). The MAO coating can improve the wear resistance and reduce the corrosion rate of magnesium alloys. During the micro arc oxidation process in the present study, the concentrations of sodium hydroxide, sodium metasilicate, sodium fluoride, copper sulfate and the applied current density and frequency were carefully controlled. Then, the influences of these controlled parameters on the structures and properties of the MAO coatings on AZ31 magnesium alloy were discussed. In order to understand the microstructures and compositions of MAO coatings, the Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) were applied in this study. Furthermore, to analyze the corrosion resistance and to define the color of MAO coatings, the potentio-dynamic polarization test and colorimeter were applied respectively. Experimental results indicate that the concentration adjustment of electrolytes will affect the structures and compositions of MAO coatings. All these MAO coatings on magnesium alloys can exhibit good surface protection. Sodium hydroxide has the most significant effect on the outer layer of the MAO coatings because it dramatically influences the conductivity of solution which apparently changes the intensity of spark during MAO process. On the other hand, sodium fluoride has the most obvious effect on the inner layer of the coatings and the corrosion resistance because it determinates whether the dense layer exists or not. But, excess sodium fluoride will interrupt the integrity of MAO coatings. Copper sulfate influences the surface colors the most without changing other properties of MAO coatings. The main electric parameters are the current density and frequency. The current density has pronounced influence on the thickness of MAO coating because it can supply different amounts of energy during MAO process. Frequency can have more obvious effect on the microstructures of MAO coatings, instead of the thickness. Its main effect is to improve the microstructure by reducing the defects within MAO coatings, hence improve the homogeneity of surface colors.
參考文獻
延伸閱讀
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