- 學位論文
LZ91 鎂合金透過微弧氧化製程改變表面色澤之研究
Study of surface color change of LZ91 magnesium alloy through processes of micro arc oxidation
摘要
鎂合金雖具有良好的物理特性，但卻具有較差的抗腐蝕與耐磨耗性及表面著色困難等弱點，而嚴重影響鎂合金之未來發展。微弧氧化技術為鎂合金表面改質新興技術之一，其技術特色在於鎂合金表面生成一氧化膜，並提升其抗腐蝕、耐磨耗特性和表面氧化膜色澤變化。 本次研究藉由LZ91 鎂合金在不同電解液之成分搭配和氧化時間以達到氧化 膜色澤變化，其電解液主軸以植酸為主，而植酸對於二價、三價陽離子之螯合能 力極為顯著。此外選用硫酸銅或過錳化鉀之不同比例，並搭配植酸之螯合特色， 以助於氧化膜之色澤變化和提升耐磨耗、抗腐蝕等特性。透過色度分析儀、SEM、 XRD、XPS、極化曲線、交流阻抗、鹽霧試驗、磨耗試驗等方式以分析不同微弧 氧化之表面形貌、氧化膜色澤、耐磨耗、抗腐蝕性之差異化。 研究結果發現，植酸之氧化膜色澤呈現灰色，且有助於氧化膜成長速率、抗腐蝕特性，然而緻密性較差，對於長期腐蝕環境下，腐蝕氣氛易透過內部孔洞侵入基材。另一方面，添加硫酸銅或過錳化鉀，其氧化膜呈現色澤則分別為70%昏灰色及駝色，但卻造成氧化膜成長速率降低且抗腐蝕、抗磨耗性略低於僅有植酸之氧化膜。 經由以上實驗結果發現，植酸電解液中適量添加硫酸銅或過錳化鉀，可有效 助於氧化膜色澤之變化，且不會顯著降低其他相關性質。
並列摘要
Magnesium alloys have good physical properties. Unfortunately, magnesium alloys exhibit a very poor corrosion resistance, wear and color of surface. These weak points will seriously influence their future development and applications. Micro arc oxidation technology, which generates on the alloy surface to develop ceramic-like oxide coatings,is one of the new surface treatments for magnesium alloys. It can remarkably promote the corrosion, wear resistance and change surface color. In this study, effects of various electrolytic compositions and oxidation times on the color change of MAO coatings of LZ91 magnesium alloys were evaluated. Phytic acid, which exhibits powerful chelating capability with di- and trivalent cations, is a main electrolytic composition in this study. Furthermore, some CuSO4·5H2O or KMnO4 is combined with phytic acid to further improve the oxide-coating color, wear and corrosion resistance. The colorimeter, SEM, XRD, XPS, potentiodynamic polarization, EIS, salt spray, pin-on-disk tribo-meter are used to analyze the MAO surface morphologies, coating colors, wear and corrosion properties. In this work, the growth rate of oxide coating in phytic acid is fast. The surface coating in phytic acid exhibits a gray color and could improve the corrosion properties of LZ91 magnesium alloys. However, the oxide coating in phytic acid is not dense sufficiently and will be penetrated easily by corrosion atmosphere after a long period in corrosion environment. On the other hand, addition of CuSO4·5H2O or KMnO4 causes coating color to exhibit 70% dim gray or camel, respectively. But the growth rate of oxide coating decreases and the wear and corrosion resistance are reduced. Based on these experimental results, the electrolyte of phytic acid with suitable content of CuSO4•5H2O or KMnO4 with phytic acid will change the colors of thin film,which properties of film will not be affected.