- 學位論文
AZ31B鎂合金鋯酸與矽氧烷複合處理之腐蝕行為研究
The Corrosion Behavior of Hexafluorozirconic Acid and Silane Composite Coating on AZ31B Magnesium Alloy
摘要
因環保節能等等的環境議題逐漸受到重視，鎂合金的高比強度、高導電導熱率、及生物可降解等等特性成為了一個未來發展的重點項目。然而鎂合金本身的高化學活性使其在應用方面增加了不少限制和條件，因此如何環保且有效的提升鎂合金的抗蝕性將是需要面對的問題。本研究嘗試使用六氟鋯酸鹽化成結合溶膠凝膠的複合製成來達到環保且抗蝕的效果。研究主要分為前後兩部分：前半將討論AZ31B經過不同pH值六氟鋯酸化成後的表面形貌及特性，後半則會討論後續進行溶膠凝膠處理後抗蝕性的變化及腐蝕行為。 研究結果發現，pH4為六氟鋯酸化成的一個重要分界，原因在ZrO2穩定存在的酸鹼值區間在pH4以上。pH4以下的化成條件使得較鈍態的雜質Al8Mn5以外的相對陽極區難以形成均勻的膜層結構而持續造成底材溶出，而雜質處因大量的還原反應有較多的ZrO2覆蓋。反之pH4以上即便在相對陽極處也可以有ZrO2沉積，而形成相對較穩定且連續的鈍化膜。其中pH值造成的ZrO2沉積成核點數量及沉積速率差異使得在不同pH值下所形成的鈍化膜結構其表面疏水性也會也有明顯不同，而表面疏水性造成的溶膠凝膠膜厚差異會大幅影響溶膠凝膠阻水阻氣的效果。 最後的腐蝕行為分析可以看到複合製成雖然可以有效提升鎂合金的抗蝕性，但Al8Mn5雜質處因不論在任何pH值下皆會因為有較厚的ZrO2沉積及劇烈的析氫反應使其周圍的膜層有較多的缺陷，因此腐蝕攻擊皆會出現在雜質附近。若要提升此複合製成的抗蝕效果，如何減少雜質造成的活性差異將會是需要解決的問題。
並列摘要
As environmental issues such as energy conservation have gradually received attention, magnesium alloys which possess high specific strength, high electrical and thermal conductivity, and biodegradability have become a key project for future development. However, the high chemical activity of the magnesium alloy adds many restrictions to its application. Therefore, how to improve the corrosion resistance of the magnesium alloy in an environmentally friendly and effective way will be essential. In this study, hexafluorozirconate acid combined with sol-gel composite production was developed to enhance corrosion resistance of AZ31B magnesium alloy. The study is mainly divided into two parts: the first half will discuss the surface morphology and characteristics of AZ31B after hexafluorozirconate conversion with different pH values, and the second half will discuss the corrosion resistance and corrosion behavior after the subsequent sol-gel treatment. The results found that pH4 is an important boundary for the formation of hexafluorozirconate conversion coating. The reason is that the pH range where ZrO2 stably exists is above pH4. The formation conditions below pH4 make it difficult for the anode region with respect to impurity Al8Mn5 to form a uniform film structure, which continues to cause the substrate to dissolve. Only the impurity is covered by a large amount of ZrO2 due to reduction reactions. While the pH is above 4, ZrO2 can be deposited at the relatively cathode region, forming a stable and continuous passivation film. In addition, the difference in the number of nucleation points and deposition rate of ZrO2 deposition caused by the pH value makes the surface hydrophobicity of the passive film significantly different. The difference in the thickness of the sol-gel film caused by the surface hydrophobicity will greatly affect the water and gas barrier effect of the sol-gel. In the last part, corrosion behavior analysis shows that although the composite process can effectively improve the corrosion resistance of the magnesium alloy, the impurity Al8Mn5 at any pH value will cause excessively thick ZrO2 deposition and intense hydrogen evolution reaction which makes the film near the impurities has more defects. To improve the corrosion resistance of the composite process, how to reduce the difference in activity caused by impurities will be a problem that needs to be solved.
參考文獻
延伸閱讀
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