奈米氧化鈦顆粒對AZ31鎂合金微弧氧化膜層腐蝕、磨耗以及光催化性能之影響

Abstract

鎂合金作為新一代的綠色材料，具有比強度高以及加工性良好等特性，廣泛應用於汽車、航空等工業應用領域。然而，鎂合金的化學活性高，抵抗腐蝕能力低，在極端環境使用中也因此受到限制，故而必須施以適當的表面改質。 在各種表面改質技術中，微弧氧化能夠在鎂合金上形成陶瓷氧化層，並藉此提升抗腐蝕和耐磨耗能力。雖然能夠有效提升鎂合金的抗腐蝕能力，但是微弧氧化層本身具有多孔結構，仍然可能讓腐蝕因子得以擴散接觸底材進而發生腐蝕。因此，為了改善微弧氧化層的多孔特性，本研究在含氟之矽酸鹽電解液系統中添加不同濃度 2.5、5.0、7.5 g/L 之奈米氧化鈦顆粒，並就製程參數對所生成微弧氧化層之抗蝕能力、微結構、化學組成及光催化效應等進行深入的探討。 根據實驗結果，隨著電解液中奈米氧化鈦顆粒濃度的增加，微弧氧化層中Rutile相含量也隨之提升，在硬度提升的同時，表面顏色也會由原先未添加奈米顆粒的白色轉為灰黑色。雖然低濃度2.5g/L的奈米氧化鈦顆粒對微弧氧化層的抗腐蝕能力並未有顯著影響，但添加高濃度7.5g/L的奈米氧化鈦顆粒可以有效填補鎂合金微弧氧化層表面之孔洞，並藉此在AZ31鎂合金表面生成具有良好障蔽保護效果之微弧氧化層，進而提升其抗腐蝕能力，同時由磨耗試驗得知，添加低濃度2.5 g/L的氧化鈦顆粒對於膜層具有提升抗磨耗能力之功用。 關鍵字: 鎂合金、微弧氧化、奈米氧化鈦顆粒、抗腐蝕測試、磨耗測試

As one of the green materials, magnesium alloys are known for their high specific strength and good workability, and thus widely used in various industrial fields, especially in automobiles and aircraft. However, magnesium alloys tend to suffer severe corrosion due to their high chemical activity, which calls for proper surface modification. Among various surface modification processes, micro-arc oxidation (MAO) can form a ceramic oxide layer on magnesium alloys to improve their corrosion resistance and wear resistance. Nonetheless, even with the elevated corrosion resistance,the porous structure of MAO coating still leaves a diffusion path for corrosive species to penetrate through the coating and react with the substrate. Therefore, in order to modify the microstructural defects in the MAO coatings, this study investigates the effect of TiO2 nanoparticle addition on the MAO process operated in a fluoride containing silicate electrolyte system, including corrosion resistance, microstructure, chemical composition, and photocatalytic effect of the coatings. The preliminary experimental results showed that the increase in the concentration of TiO2 nanoparticles increased the number of Rutile-TiO2 in the MAO coating, which results in both an elevated hardness and a change in color from white to gray-black. As observed in electrochemical impedance spectroscopy (EIS), the addition of 2.5g/L TiO2 of nanoparticle exhibits no significant influence on the corrosion resistance and the total impedance is around 107 kΩcm2. However, the coating formed with a high concentration 7.5g/L of TiO2 nanoparticles performs better corrosion resistance which elevates the total impedance to over 600 kΩcm2 and the defects within are effectively reduced. In addition, low concentration of 2.5 g/L TiO2 exhibits the improve the wear resistance property. Keywords: Magnesium alloy, micro-arc oxidation, TiO2 nanoparticles, EIS, wear resistance.