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|標題:||富鋁相組織對熱室法壓鑄AZ91D鎂合金薄板 之腐蝕性質影響及應用其易腐蝕特性 製造再生氫氣能源之評估
Effect of Al-rich α Phase on the Corrosion Properties of the Hot Chamber Die-Casting AZ91D Plate and Evaluation of the Corrosion Characteristic for Hydrogen Generation
|關鍵字:||Magnesium;鎂合金;Al-rich a phase;Ni-rich AZ91D;corrosion;hydrogen;富鋁相;高鎳AZ91D;腐蝕;氫氣||出版社:||材料工程學研究所||摘要:||
富鋁相組織分佈於壓鑄AZ91D薄板表面之die skin層，造成壓鑄AZ91D薄板抗腐蝕性不佳。前人研究在鎂合金中若鐵含量增加則抗腐蝕能力下降。本研究以SEM-EDS分析壓鑄薄板表面富鋁相組織，發現其含鐵量(3.9wt%)遠高於壓鑄薄板整體之平均鐵含量(0.005wt%)；為進一步確定鐵含量與富鋁相組織之間的腐蝕關係，本實驗自行熔煉出兩含鐵量不同之富鋁相/β相複合相合金塊材，並進行進行電化學腐蝕試驗；實驗結果後發現高含鐵量之富鋁相/β相複合相合，其腐蝕電流密度值高達800~2000μA/cm2；而低含鐵量之富鋁相/β相複合相合，其腐蝕電流密度值僅為67~90μA/cm2。由此可推證富鋁相組織抗腐蝕性不佳之主要原因為高含鐵量或高Fe/Mn含量比值。AZ91D在NaCl水溶液中的腐蝕速率與氫氣產生速率呈線性正比之關係，故本研究以高含鐵量之富鋁相/β相複合相合金塊材以及Ni-rich AZ91D，個別在NaCl水溶液中反應而產生氫氣，並同時以白金線觸媒加速其氫氣反應速率。實驗結果：在室溫5%NaCl水溶液中產生500ml的氫氣所需時間不超過800sec，若增加NaCl水溶液之濃度或溫度則氫氣產生速率更為提高；各試片完成製氫試驗後之重量損失介於0.29g~0.62g。為證實本實驗所製造之氣體大部分為氫氣，在氣體製造的過程中將氣體釋放出，同時點燃此氣體使之持續燃燒。實驗結果發現在點燃氣體之瞬間產生微量之爆炸聲，此為燃燒之氫氣與空氣中之氧氣反應結果，之後氣體便持續燃燒。製氫試驗後之粉末經低掠角XRD分析，其繞射圖譜比照JCPDS card後，得知主要繞射峰均代表(Mg(OH)2)，由此可證實此副產物為氫氧化鎂。本實驗不僅提供了一種製氫方式，同時亦可望改善高鎳廢棄AZ91D回收之問題。
The reason of the corrosion resistance decreasing of the die-cast AZ91D was the Al-rich α phase distributed in the die skin layer on the surface. In previous study, increasing the iron content caused the corrosion resistance decreasing of the Mg alloy. It was found that iron content (3.9wt%) in the Al-rich α phase distributed in the die skin layer on the die-cast AZ91D surface was greater than in the die-cast AZ91D's average(0.005wt%) by the SEM-EDS analysis. To explore the corrosion relationship between the Fe content and Al-rich α phase, we melted two of the Al-rich α/ β composite phase alloys which had different Fe contents. After the polarization test on the Al-rich α/ β composite phase alloys, the current density (800~2000μA/cm2) with higher Fe content was greater than with lower Fe content (67~90μA/cm2). According the results, the reason of the corrosion resistance decreasing of the Al-rich α phase was its high iron content. The relationship between the corrosion rate and the hydrogen evolution rate of the Ni-rich AZ91D was shown as linear and positive. The Al-rich α/ β composite phase alloys and the Ni-rich AZ91D were used to generate the hydrogen with platinum wire catalyst in NaCl solution. As the experiment result, the hydrogen volume created from zero to ~ 500ml spent no more than 800sec in 5%NaCl solution in room temperature. The weight losses of the samples for hydrogen generation were in range of the 0.29g~0.62g. To prove the gas we generated was mostly hydrogen, the gas was ignited during the process. A slight burst is heard and the gas keeps burning afterward. This is due to the reaction between the hydrogen and the oxygen in the atmosphere. The by-product was analyzed by the Grazing Incident X-ray diffraction and proved as (Mg(OH)2) after comparing diffraction pattern. The present study might not only suggest a method to generate hydrogen but also promote the recycling of used magnesium products that were originally plated with Ni on their surface.
|Appears in Collections:||材料科學與工程學系|
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