臺灣博碩士論文加值系統

本研究選用A357和A201鋁合金做為研究材料，分別在砂模鑄造過程中外加不同強度交流磁場。並藉由顯微組織觀察與機械性質分析，探討外加交流磁場對砂模鑄造A357和A201機械性質影響與晶粒細化效應。
不論A357或A201在外加磁場下，隨磁場上升晶粒尺寸均隨之細化，A357及A201最小晶粒尺寸均出現在5.55 mT。而A357晶粒細化較A201明顯，原因推測為兩者初晶形狀所致，A357的初晶較於A201的初晶形狀更易於因攪拌破碎，進而提供更多的異質成核點。結果顯示不論A357或A201在未外加磁場下試片外圍和中心都有晶粒尺寸分布不均的現象，在外加磁場攪拌過後熔湯產生的質傳效應而有所改善使試片晶粒尺寸分布均勻。
A201和A357洛氏硬度測量結果均隨外加磁場強度提升而硬度提升。A201拉伸試驗顯示最大抗拉強度、降伏強度和伸長率在外加磁場上升後均提升，其中最佳機械性質表現出現在5.55 mT，並且隨著磁場攪拌效果提升使鑄材誤差明顯縮小，良率上升。而A357因隨磁場強度上升共晶區域的共晶形成導致攪拌紊亂會越嚴重進而產生空孔，磁場強度達到1.45mT時因晶粒尺寸已有初步細化，且共晶區域空孔數大幅小於較高磁場強度鑄材，使其最佳機械性質表現出現在1.45mT。
由XRD結果可發現無論是A357或是A201均因晶粒成核後因外加交流磁場而旋轉，使平行磁場面測量結果可發現α-Al相具有(111)的優選取向，在垂直磁場面測量呈現隨機取向的結果。

In this study, A357 and A201 aluminum alloys were used as the research materials, prepared by sand casting process with different intensity AC magnetic field. The effects of external magnetic field on the mechanical properties and grain refinement of A357 and A201 were investigated by microstructure observation and mechanical testing.
The minimum grain size of A357 and A201 can be obtained at 5.55 mT, and the grain refinement of A357 is more significant than A201, The reason is due to the different shape of primary crystals for both alloys. The results showed that the uneven distribution of the grain size of A357 and A201 alloys cast under magnetic field can be improved.
Rockwell hardness test results showed that the hardnesses of A201 and A357 alloys increased when increasing the external magnetic field intensity. According to the tensile test results, the ultimate tensile strength, yield strength and elongation were improved when the external magnetic field intensity was increased. The optimal mechanical properties appeared when cast at magnetic field intensity of 5.55 mT. A357 alloy cast at the higher magnetic field intensity, the lager shaking during cast could be more serious. Therefore, the holes were formed around the eutectic phases. The optimal mechanical properties appeared at magnetic field intensity of 1.45 mT. Because the grain size have been refined and therefore the numbers of holes in eutectic phases were less than the alloy cast under high magnetic intensity.
According to the XRD results, both A357 and A201 alloys displayed the higher preferred orientation of (111) α-Al phase along the direction of parallel magnetic field. The reason is proposed that the nucleation of grains were rotated by applying the magnetic field.

摘要 I
Abstract II
總目錄 III
表目錄 IV
圖目錄 V

第一章 緒論 - 1 -
1-1 前言 - 1 -
1-2 研究動機 - 3 -

第二章 文獻回顧 - 5 -
2-1 鋁合金簡介 - 5 -
2-2 鋁合金命名 - 7 -
2-3 鋁合金鑄造 - 9 -
2-4 砂模鑄造 - 11 -
2-5 鑄造晶粒細化 - 12 -
2-5-1 控制降溫速度（Thermal method） - 12 -
2-5-2 添加晶粒細化劑（Chemical method） - 14 -
2-5-3 外力攪拌 (Mechanical method) - 17 -
2-6 磁場與晶粒細化 - 20 -
2-7 晶粒尺寸對機械性質的影響 - 21 -
2-8 結晶優選取向 - 22 -
2-9 電磁場與結晶優選方向 - 22 -
2-10 外加電磁場與鑄造 - 24 -

第三章 實驗流程 - 31 -
3-1 材料製備 - 31 -
3-2-1 光學顯微鏡(Optical microscope, OM)分析 - 35 -
3-2-2 枝晶臂間距(Dendrite Arm Spacing, DAS)測量 - 37 -
3-2-3 掃描式電子顯微鏡(Scanning electron microscope,SEM)分析- 38
3-3 機械性質分析 - 39 -
3-3-1 洛氏硬度機Mitutoyo AR-10 - 39 -
3-3-2 拉伸測試 - 39 -
3-4結構分析 - 41 -
3-4-1 X光繞射( X-Ray diffraction, XRD)分析 - 41 -

第四章 結果與討論 - 43 -
4-1 A357和A201 原鑄材之顯微結構 - 43 -
4-2 A357和A201 外加交流磁場鑄材之顯微結構 - 46 -
4-3 A357和A201 外加交流磁場鑄材之機械性質 - 49 -
4-4 A357和A201 外加交流磁場鑄材之XRD分析 - 58 -
4-5 A357和A201 外加交流磁場鑄材之優選取向產生機制 - 61 -

第五章 結論 - 69 -

第六章 參考文獻 - 71 -

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