鎂合金為具備十足應用潛力的新興材料之一，可用於運輸、工程、3C、醫療、運動用品等，實現強度不變的材料輕量化。惟其抗蝕性受到鎂本身相對低的還原電位影響，使其於一般含水環境中極為活潑，抗蝕性成為鎂合金應用上必須克服的主要課題。鎂的腐蝕行為受到許多因素影響，且人們對於鎂腐蝕的詳細機制仍有許多不清楚的地方。因此本論文將針對合金結晶取向和鋯元素添加對鎂合金腐蝕性質之影響進行研究，並著重於合金腐蝕微結構和腐蝕行為之間的關聯。
結晶取向方面，本研究使用經輥軋之AZ31鎂合金來探討不同軋向之結晶取向對腐蝕性質的影響。透過X光繞射(XRD)圖譜、背向散射電子繞射(EBSD)等確認樣品之結晶取向分布後，以開路電位(OCP)量測、電化學阻抗頻譜(EIS)、動態極化曲線、析氫反應速率等電化學腐蝕測試針對合金瞬時和長期之腐蝕行為、腐蝕速率、及腐蝕膜層狀態進行分析，並透過臨場光學顯微鏡(in situ OM)和掃描式電子顯微鏡(SEM)記錄樣品表面巨觀腐蝕形貌及微觀腐蝕形態之異同。研究結果顯示不同軋面之結晶取向與分布對腐蝕速率有顯著影響。AZ31鎂合金表面腐蝕形貌以局部腐蝕為主，而局部腐蝕主要沿輥軋方向擴展。基面為主之表面局部腐蝕擴展速率較稜面為主之表面來得慢；而當樣品表面同時具有基面和稜面晶粒混合出現時，平面間會產生伽凡尼效應，進而導致此種樣品在腐蝕初期具有更快的腐蝕速率。
鋯(Zr)通常用作鎂合金的晶粒細化劑使用。在大多數情況下，鋯僅作為合金熔煉之輔助添加劑，其對腐蝕性質的影響常被其他合金元素的效應所覆蓋。因此本研究旨在了解鋯添加對兩種不同鋯含量(0.037 wt%和0.208 wt%)的二元鎂鋯合金腐蝕行為之影響。研究中使用掃描式電子顯微鏡(SEM)和能量散布X 光光譜(EDS)研究合金中的含鋯顆粒分佈和成分差異，並使用掃描開爾文探針力顯微鏡(SKPFM)用於了解鋯顆粒和鎂底材間的伏塔電位差。之後使用臨場光學顯微鏡(in situ OM)結合開路電位量測記錄合金腐蝕形貌的演變，並以電化學阻抗頻譜(EIS)對腐蝕膜層進行分析，和析氫速率測試定量合金腐蝕速率。最後針對特定腐蝕形貌區域的鋯顆粒，以聚焦離子束(FIB)/SEM/EDS分析，探討腐蝕形貌與合金表面鋯顆粒的尺寸、分布、以及鐵含量間的關係。鋯含量0.208 wt%的樣品，鋯顆粒尺寸較大，含鐵量較多，且鋯顆粒與鎂底材之間的伏塔電位差也較大。析氫試驗顯示鋯含量0.208 wt%樣品的腐蝕速率較鋯含量0.037 wt%樣品快上許多。在兩種樣品中可以觀察到鋯顆粒的尺寸和含鐵量在超過一定的大小和比例後，會對鋯顆粒與底材間的伏塔電位差有顯著的提升，進而產生嚴重的析氫反應和局部腐蝕，證實二元鎂鋯合金中局部腐蝕的驅動力主要來自於鋯顆粒所提供的伽凡尼效應。

Magnesium alloys are one of the emerging materials with various potential applications. They can be used in transportation, engineering, 3C, medical and sports equipment to achieve lightweight while maintaining strength. However, owing to the low reduction potential of magnesium, it is extremely active in aqueous environments, and its corrosion resistance has become the main problem that must be overcome for practical applications. The corrosion behavior of magnesium is affected by different factors, and the corrosion mechanism of magnesium is still not fully understood. Therefore, in this study, the effects of crystal orientation and zirconium addition on the corrosion properties of magnesium alloys will be investigated, focusing on the correlation between corrosion microstructure and corrosion behavior.
For crystal orientation, this study used rolled AZ31 magnesium alloys to study the effect of crystal orientation from different directions with respect to rolling on the corrosion properties. After confirming the crystal orientation distribution of the samples through X-ray diffraction (XRD) and electron backscatter diffraction (EBSD), electrochemical corrosion tests, including open circuit potential measurements, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and hydrogen evolution rate, are performed to study the instantaneous and long-term corrosion behavior, corrosion rate, and properties of the corrosion film. The similarities and differences of both macroscopic and microscopic corrosion morphologies on the samples were observed by in situ optical microscopes (OM) and scanning electron microscopes (SEM). The results show that crystal orientation on different directions with respect to rolling has a significant effect on the alloy corrosion rate. The corrosion morphology on the surface of AZ31 magnesium alloys is mainly localized corrosion, and the localized corrosion propagates along the rolling direction. The localized corrosion propagation rate on the basal plane is slower than that on the prismatic plane. And when the sample has a mixture of basal and prismatic planes, the galvanic effect between these planes leads to a faster corrosion rate of the sample in the early stage.
Zirconium (Zr) is commonly used as a grain refiner for Mg alloys. However, in most cases, Zr was added as a secondary additive, by which the effect on the corrosion properties would be shadowed by other alloying elements. Therefore, this research aims to elucidate the effect of Zr addition on magnesium corrosion with two binary Mg-Zr alloys with different Zr concentrations (0.037wt% and 0.208wt%). In this study, scanning electron microscopes (SEM) with X-ray energy dispersive spectroscopy (EDS) were used to study the Zr distribution and compositional differences in the alloys. Scanning Kelvin probe force microscope (SKPFM) was used to reveal the Volta potential difference between the Zr particles and the Mg matrix. In situ optical microscopes (OM) combined with open circuit potential monitoring were used to record the alloy corrosion morphology evolution. And through electrochemical impedance spectroscopy (EIS) analysis and hydrogen evolution tests, the properties of the surface corrosion film and the alloy corrosion rates were analyzed. Finally, with focused ion beam (FIB)/SEM/EDS analysis, the size, distribution, and Fe content of the zirconium particles on the alloy surface are correlated to the corrosion behavior and morphology. For the sample with 0.208 wt% Zr, the Zr particles are larger and contain more Fe, with a larger Volta potential difference between the Zr particles and the Mg matrix. Hydrogen evolution tests show that the corrosion rate of the 0.208 wt% Zr sample is faster than that of the 0.037 wt% Zr sample. In these two alloys, it can be observed that when the size and iron content of the zirconium particles reach a critical value, it will significantly increase the Volta potential difference between the zirconium particles and the Mg matrix, resulting in severe hydrogen evolution reaction and localized corrosion. It can be concluded that the driving force of localized corrosion on binary Mg-Zr alloys mainly comes from the microgalvanic effect provided by the Zr particles.

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