本研究的目的在於探討不同釔添加量之二元鎂釔合金，其微結構差異對於腐蝕性質的影響。首先利用ICP-MS、XRD、SEM等對鎂釔合金樣品進行微結構的觀察。結果顯示Mg-1wt%Y樣品所含的鐵雜質元素遠大於其容許極限，且以雜質顆粒的形式隨機分布在樣品表面；Mg-7wt%Y樣品則具有含鋯的雜質顆粒，而釔則主要以連續網狀的Mg24Y5二次相分布於晶界上。
接著透過電化學量測搭配臨場光學顯微鏡監測樣品腐蝕電位和表面腐蝕形貌隨浸泡時間的演變。在Mg-1wt%Y的樣品上可觀察到嚴重的局部腐蝕，且擴展十分迅速；相比之下，Mg-7wt%Y的樣品上局部腐蝕擴展則較為緩慢，且其腐蝕速率隨著時間的進行並沒有太大的改變。
最後通過SEM/FIB系統進一步觀察腐蝕微結構之差別。結果顯示Mg-1wt%Y樣品的局部腐蝕受鐵雜質所主導且在擴展過程無阻礙，可輕易擴展至整個樣品表面；而Mg-7wt%Y樣品則由鋯顆粒的伽凡尼效應主導局部腐蝕的進行，但局部腐蝕的擴展會受到Mg24Y5二次相的阻擋，因此導致擴展過程較為緩慢。鎂釔合金隨著釔添加量的提高，會在晶界上形成連續網狀的二次相結構，其對於阻擋局部腐蝕的擴展及提昇合金抗蝕性有正面的影響。

The purpose of this study is to investigate the influence of alloy microstructure on the corrosion properties of binary magnesium-yttrium alloys with different yttrium additions. Firstly, ICP-MS, XRD, and SEM were used to study the microstructure of magnesium-yttrium alloy samples. The results show that the Mg-1wt%Y sample contains iron impurity far greater than the tolerance limit, and they are randomly distributed along the surface as impurity particles; while the Mg-7wt%Y sample contains impurity particles with zirconium, and the yttrium is mainly present in the continuous network Mg24Y5 second phase distributed on the grain boundaries.
Then, the evolution of corrosion potential and surface corrosion morphology of the samples with immersion time was monitored through electrochemical measurements and in situ optical microscopy. Severe localized corrosion was observed on the Mg-1wt%Y sample with rapid expansion. In contrast, the expansion of localized corrosion on the Mg-7wt%Y sample is slower, and the corrosion rate does not change much with immersion time.
Finally, the difference in corrosion microstructure was studied by SEM/FIB system. The results show that the localized corrosion on the Mg-1wt%Y sample is dominated by iron impurities and can easily expand to the entire sample surface without much hinderance. On the other hand, the localized corrosion on the Mg-7wt%Y sample is dominated by the galvanic effect of the zirconium particles, but its expansion was blocked by the Mg24Y5 second phase, which leads to a slower expansion rate. With increasing amount of yttrium addition, continuous network-like second phase can form on the grain boundaries in magnesium-yttrium alloy, which has a positive effect on blocking the localized corrosion expansion and improving the corrosion resistance.

致謝 I
摘要 II
Abstract III
目錄 V
圖目錄 VIII
表目錄 XII
第一章 緒論 1
第二章 文獻回顧 3
2.1 鎂合金簡介 3
2.2 鎂合金命名 4
2.3 常見添加於鎂合金的合金元素 4
2.3.1 鋁(Al) 6
2.3.2 錳(Mn) 6
2.3.3 鋅(Zn) 6
2.3.4 鋯(Zr) 6
2.3.5 稀土元素(rare earth elements, RE) 7
2.4 鎂的雜質容許極限(tolerance limit) 7
2.5 鎂的腐蝕機制 9
2.6 鎂的局部腐蝕機制 10
2.7 添加釔對鎂的影響 12
2.8 鎂釔合金的腐蝕 13
第三章 實驗方法與步驟 16
3.1 實驗流程 16
3.2 實驗材料及前處理 17
3.3 合金成分分析與微觀組織觀察 18
3.4 腐蝕膜成分分析 19
3.5 晶體結構分析 19
3.6 浸泡測試 20
3.6.1 浸泡去離子水 20
3.6.2 浸泡0.1M氯化鈉水溶液 20
3.7 電化學量測及臨場光學顯微鏡觀察 20
3.7.1 開路電位(OCP)量測 22
3.7.2 動態極化掃描 22
3.7.3 電化學阻抗分析(EIS) 23
3.8 析氫反應(hydrogen evolution) 24
3.9 橫截面聚焦離子束微觀組織觀察 26
第四章 實驗結果與討論 27
4.1 鑄造鎂釔合金顯微組織 27
4.1.1 鎂釔合金化學組成 27
4.1.2 鎂釔合金XRD分析 28
4.1.3 鎂釔合金微結構觀察 29
4.1.4 鎂釔合金金相觀察 31
4.2 鎂釔合金之腐蝕性質 32
4.2.1 鎂釔合金開路電位隨浸泡時間之變化及臨場OM觀察 32
4.2.2 鎂釔合金腐蝕速率測試 34
4.2.3 電化學阻抗分析(EIS) 38
4.3 鎂釔合金腐蝕微結構 41
4.3.1 腐蝕膜結構及化學組成分析 41
4.3.2 鎂釔合金浸泡去離子水SEM觀察 46
4.3.3 鎂釔合金SEM/FIB腐蝕觀察 49
4.4 鎂釔合金腐蝕機制討論 58
第五章 結論 64
第六章 未來展望 65
參考資料 66

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