- 學位論文
鎂合金AZ31鋁基化成處理之研究
Aluminum-Based Conversion Coatings on AZ31 Magnesium Alloys
摘要
鎂合金本質上具有高比強度及優異生物相容特性，極具潛力適用於汽車工業、3C電子產品及生物植體上。惟因鎂合金其化學特性極為活潑，在一般使用的使用環境中，無法生成緻密的腐蝕氧化膜，以保護鎂合金底材，避免受到腐蝕因子的攻擊，因此提升抗蝕性，為鎂合金應用上，迫需解決的關鍵問題。本研究主要分為兩個部分: 第一部分為架設自製的即時氣體收集及影像記錄系統，並且透過此系統研究鎂合金AZ31在不同水溶液環境中的腐蝕行為，第二部分則為鎂合金AZ31化成處理的溶液設計，並將無毒三價鋁離子，應用於水溶液化成系統中，試圖取代傳統中化成溶液中的六價鉻物種，並討論後處理製程，對於化成皮膜的抗蝕能力的提升。經由實驗發現，實驗室的自製系統，明顯觀察到鎂合金AZ31在含氯離子的溶液中，出現明顯的腐蝕前沿，並且腐蝕前沿擴展的速率與陰極析氫電流密度高度相關。化成處理部分為鎂合金AZ31經由添加磷酸二氫鉀的硫酸鋁溶液化成處理，或是單一鋁鹽化成處理，再經矽酸鈉後處理後，兩者的抗蝕能力表現，皆相較未經處理的底材，極化阻抗提升約一個數量級。
並列摘要
Magnesium possesses high specific strength and biocompatibility, hence, with potential to be applied in automobile industry, commercial electronics, and bio-implant. Nonetheless, magnesium is limited for high chemical activity and porous film naturally-formed without prevention for corrosion media attack. Corrosion resistance enhancement is, therefore, the critical problem required to solve in magnesium for various application. This study has been divided in to two parts: Part1 mainly comprises the set-up of real-time gas collection equipment with video recorder and magnesium AZ31in various aqueous environment studied through this equipment. Part2 focus on the design in chemical conversion coatings solution, in attempt to substitute non-toxic trivalent aluminum for highly toxic hexavalent chromium species. As result, the corrosion fronts apparently formed when AZ31 in chloride containing solution, and the propagation for corrosion fronts is apparently related to hydrogen evolution rate in observation. Conversion coatings formed in aqueous solution containing aluminum sulfate with potassium dihydrogen phosphate, and single aluminum salt with silicate post-treatment both highly improved the corrosion resistance. (estimated by polarization resistance and corrosion current density showing that approximately one order improvement).