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Effect of Reactions between Fly Ash and Al-3Mg Melt on the Microstructure and Hardness of Aluminum Matrix Composites
|Authors: ||Liang-Jing Fan|
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
microstructure;aluminum matrix composite;fly ash;chemical reaction
|Issue Date: ||2017-05-24T08:23:53Z
|Abstract: ||飛灰與液相鋁的化學反應過程，飛灰顆粒逐漸分解及原位自生成複合材料的增強材已被證實。在本研究中，以攪拌鑄造製作的Al-3Mg/5 wt.%飛灰複合材料加熱至850℃施予不同的反應時間0、10、20、30、40小時，探討化學反應對複合材料微觀結構及硬度之影響。飛灰與Al-3Mg合金的化學反應的研究，使用光學顯微鏡、能量散射光譜儀、X-射線繞射儀、X-射線光電子能譜儀進行複合材料的微觀結構分析。複合材料性質評估工作包括密度檢測、孔隙率計算及勃氏試驗。 實驗結果顯示反應30小時之後，大部分的飛灰顆粒被還原反應分解及原位自生成Al2O3及MgAl2O4。還原反應使飛灰釋放Si，達到一定量後將與基材中的Mg形成Mg2Si 相析出強化複合材料。顯微組織顯示在飛灰壁緣破碎後熔湯將會滲入非實心顆粒內部的孔及裂縫，進而降低複合材料的孔隙率。複合材料隨著化學反應時間增加能降低孔隙率、並提升複合材料密度及BHN硬度值。反應40小時後，複合材料的硬度值達到最高的BHN 70.74，相較於未強化合金提升46.7 %。|
During the reactions between fly ash and Al melt, fly ash particles progressively disintegrate in the in-situ-generated reinforcement of composites. In this study, Al-3Mg/5 wt.% fly ash composites were prepared through stir casting with reactions at 850 °C for various durations 0, 10, 20, 30, and 40 h. The effects of the reactions on the microstructure and hardness of the composites were investigated. These chemical reactions between the fly ash and Al-3Mg melt were studied through microstructure analysis of composites by optical microscopy, energy-dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. The density, porosity and Brinell hardness number (BHN) of composites were evaluated on all of the Al matrix and composites. The experiment indicated that after a 30-h reaction most of the fly ash particles were decomposed because of a reduction reaction, in situ-generated θ-Al2O3, and MgAl2O4. In reduction reactions, the fly ash released the Si in the melt. A sufficient quantity of Si formed an Mg2Si phase with the Mg of the melt for precipitation strengthening. Microstructural observations revealed that after the wall of fly ash particles cracked, molten metal infiltrated the pores and cracks in the nonsolid fly ash particles. Increasing the reaction time reduced the porosity in the Al matrix composites, whereas the density and BHN were increased. After a 40-h reaction, the composite exhibited a maximal hardness of BHN 70.74, which was an improvement of 46.7% over that of unreinforced alloys.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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