臺灣博碩士論文加值系統

為拓展鎂合金於3C產品與運輸工具上之應用，添加微量高純度稀土元素( Rare earth) Ce 及 La，藉此提高輕金屬鎂合金於室溫、高溫的機械性質，並以鑄造配置Mg97Zn2La1、Mg97Zn2Ce1與Mg97Zn2La0.5Ce0.5合金。鑄造材會產生大量樹枝狀晶( dendrite )結構，造成室溫拉伸強度明顯不足，降伏強度只有120MPa左右，本研究以滾軋的方式給予材料大量變形量，使枝狀晶結構能斷裂並分散於合金中，在773K下軋延量可達到90%，使合金室溫降伏強度提升至300MPa以上。經光學顯微鏡( Optical Microscope )下觀察三者顯微組織，鎂相以樹枝晶結構組成，並在晶界上形成二次相，藉由維克氏硬度機測試，皆可發現材料之二次相硬度高於鎂基材硬度約4倍，此為三種合金高強度之主因，強化機制屬於散佈強化，經XRD分析結果得知，此類二次相為Mg12Ce1及Mg12La1；並計算經高溫滾軋673K下50%、723K下70%及773K下90%最大軋延量比較二次相分散程度對機械性質之變化。

In order to expand the application of magnesium alloys in 3C products and the transportation field, small amount of high purity rare-earth element added magnesium alloys were investigated. In this research, the Mg97Zn2Ce1, Mg97Zn2La1 and Mg97Zn2Ce0.5La0.5 alloy billets were prepared by vacuum casting. Due to the large quantity of huge dendrite structures and large size of secondary phases, the tensile yield strengths of all alloys were low around 120MPa. In this study, hot rolling processes combining the different rolling temperatures and rolling reduction were adopted for trying to refine the secondary phases. After hot rolling at 773K with 90% reduction, the yield strength of magnesium alloy can be increased to more than 300MPa. The microstructures were observed by optical microscope. The magnesium matrix displayed the large dendritic structure, while the secondary phases existed at the grain boundary of magnesium. According to the nano-indentation test result, the second phase possesses much higher hardness than the matrix. As a consequence, the strengthening mechanisms were proposed as the dispersion strengthening. In the XRD results, the secondary phases were identified as Mg12Ce1 and Mg12La1. The dispersion levers of different hot rolling processes were measured, and compared with the mechanical properties.

總目錄
摘要 I
ABSTRACT II
總目錄 III
表目錄 V
圖目錄 VI
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鎂合金簡介 5
2-2 合金元素的添加對鎂合金性質之影響 8
2-2-1 鋅(Zn)元素 8
2-2-2 稀土元素(Rare earth, Re) 9
2-2-2-1 稀土元素的介紹 9
2-2-2-2 稀土符號 10
2-2-3 稀土元素添加之影響 9
2-2-4 稀土鎂合金及其應用 12
2-2-4-1 Mg-Al-RE (AE系)合金 12
2-2-4-2 Mg-RE-Zr(EK系)合金 12
2-2-4-3 Mg-Y-RE(WE系)合金 13
2-2-4-4 Mg-Zn-RE(EZ系)合金 14
2-2-5 Mg-Zn-Y合金 14
2-2-6 Mg-Zn-Ce及Mg-Zn-La 合金 18
2-2-7 鑄造材鎂合金樹枝狀晶粒結構 (dendritic grains) 20
2-3熱機處理對鎂合金的影響 22
2-3-1 鎂合金晶粒細化 22
2-3-2 鎂合金熱機處理細化晶粒 22
2-4 分散強化 26
2-4-1散佈程度(DL, dispersion level) 26
2-4-2 高溫軋延(Hot rolling) 26
第三章 實驗方法 29
3-1 材料製備 29
3-1-1 鎂合金熔煉(Melting) 29
3-1-2 感應耦合電漿質譜分析儀(ICP-MS) 30
3-1-3 均質化 31
3-1-4 熱軋延製程(Hot rolling) 32
3-2 顯微組織觀察 33
3-2-1 光學顯微鏡(Optical microscope, OM)分析 33
3-2-2 掃描式電子顯微鏡(Scanning electron microscope, SEM)分析 35
3-3 機械性質分析 36
3-3-1 維克氏硬度機Mitutoyo HM-101 36
3-3-2 拉伸測試 36
3-4結構分析 39
3-4-1 X光繞射( X-Ray diffraction, XRD)分析 39
第四章 實驗結果 41
4-1 MG97ZN2CE1、MG97ZN2LA1、MG97ZN2CE0.5LA0.5 鑄造材經均質化後分析 41
4-1-1 顯微組織觀察 41
4-1-2 X-ray 繞射圖譜分析 45
4-1-3 室溫機械性質分析 46
4-1-4 高溫機械性質分析 48
4-1-5 鑄造材拉伸破斷面觀察 49
4-2 MG97ZN2CE1、MG97ZN2LA1、MG97ZN2CE0.5LA0.5 合金最大軋延率下熱軋延之分析 53
4-2-1 顯微組織觀察 53
4-2-2 X-ray 繞射圖譜分析 57
4-2-3 室溫機械性質分析 59
4-2-4 高溫機械性質分析 61
4-2-5 熱軋延後材料拉伸破斷面 64
第五章 結論 75
第六章 參考文獻 77

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