鎂鋰合金有良好的室溫成型性，但因為添加鋰元素使強度下降，因此本研究採用LZ91與LAZ941合金作為研究對象，進行不同旋轉速度之摩擦攪拌製程(FSP)與FSP之後再進行冷加工，探討經過不同製程處理其機械性質與顯微組織的影響。經摩擦攪拌製程後晶粒均有明顯細化， FSP-LZ91 100rpm有最小的晶粒尺寸為8.9μm，是由於轉速較低因此摩擦所產生的熱輸入較低的關係，其在拉伸結果也顯示有最佳的降伏強度與最大抗拉強度，分別為137.6MPa和150.8MPa，這與Hall-Petch方程相符合，晶粒尺寸越小降伏強度越大。而FSP-LAZ941則與LZ91有相反的現象，在300rpm時則有最佳的強度，其降伏強度與最大抗拉強度分別為187.7MPa和221.0MPa，是由於θ-Li2MgAl相出現的關係。在FSP經過軋延後，因為大量的塑性變形，使合金有明顯晶粒細化與加工硬化現象，所以材料強度均大幅提升，但因為冷加工關係導致延伸率下降，FSP-LAZ941 300rpm CR40%為最佳，硬度值為89.9HV，降伏強度為229.6MPa，最大抗拉強度為298.5MPa。從SEM破斷面分析，可知摩擦攪拌製程後，呈現許多小蜂窩狀組織。

Magnesium-lithium alloy has good room temperature formability, but its strength is low due to lithium addition. In this study, the mechanical properties and microstructures of LZ91 and LAZ941 alloys after the friction stir process (FSP) with different rotational speeds and subsequent cold rolling on FSP were investigate. The results show that the grains are remarkably refined after FSP. The minimum grain size of FSP-LZ91 100rpm is 8.9μm, which is due to the lower heat input at a lower rotation speed. It also displays the best yield and ultimate tensile strengths, which are 137.6 MPa and 150.8 MPa, respectively. It is consistent with the Hall-Petch equation, the smaller grain size the greater yield strength. On the other hand, the FSP-LAZ941 has the contrary phenomenon compare with the LZ91, and has the best strength after FSP at a higher rotation speed of 300 rpm, and its yield strength and ultimate tensile strength were 187.7MPa 221.0MPa, respectively. The reason was considered that the precipitation of θ-Li2MgAl phase occur during the FSP at higher rotation speed. After the subsequent cold rolling on FSP, the alloys show the obvious grain refinement and the work hardening due to the large amount of plastic deformation. The mechanical properties were improved, but the elongation decreased. FSP-LAZ941 300rpm following CR40% cold rolling displays optimal properties. The hardness was 89.9HV; yield strength and ultimate tensile strength were 229.6MPa and 298.5MPa, respectively. From the SEM fracture analysis results, the fracture surfaces show the dimple structures.

摘要 I
Abstract II
總目錄 III
圖目錄 V
表目錄 VIII

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鎂合金介紹 5
2-2添加合金元素對鎂合金之影響 6
2-2-1鋰(Li)元素 7
2-2-2鋁(Al)元素 7
2-2-3鋅(Zn)元素 8
2-3鎂合金的強化 8
2-4摩擦攪拌製程(Friction stir processing) 10

第三章 實驗方法及實驗步驟 23
3-1實驗設備 23
3-2材料製備 23
3-2-1鎂合金熔煉 23
3-2-1-1 LZ91熔煉及擠製製程 23
3-2-1-2 LAZ941熔煉及熱軋延製程 24
3-2-2感應耦合電漿放射光譜儀(ICP-OES) 24
3-2-3摩擦攪拌製程(Friction Stir Processing, FSP) 24
3-2-4冷軋延製程(Cold Rolling) 24
3-3顯微組織觀察 25
3-3-1光學顯微鏡分析(Optical microscope, OM) 25
3-3-2掃描式電子顯微鏡(Scanning electron microscope, SEM) 26
3-4結構分析 26
3-4-1 X-ray晶體結構分析 26
3-5機械性質測試 26
3-5-1維克氏硬度測試 26
3-5-2拉伸測試 27

第四章 實驗結果與討論 39
4-1 擠型材LZ91、FSP-LZ91及FSP-LZ91經冷軋延 39
4-1-1擠型材LZ91與FSP-LZ91 39
4-1-1-1 X-ray繞射圖譜分析 39
4-1-1-2 顯微組織觀察 39
4-1-1-3機械性質測試 39
4-1-2 FSP-LZ91經冷軋延 41
4-1-2-1 X-ray繞射圖譜分析 41
4-1-2-2顯微組織觀察 41
4-1-2-3機械性質測試 41
4-2 熱軋材LAZ941、FSP-LAZ941及FSP-LAZ941經冷軋延 43
4-2-1熱軋材LAZ941與FSP-LAZ941 43
4-2-1-1 X-ray繞射圖譜分析 43
4-2-1-2顯微組織觀察 43
4-2-1-3機械性質測試 44
4-2-2 FSP-LAZ941經冷軋延 45
4-2-2-1 X-ray繞射圖譜分析 45
4-2-2-2顯微組織觀察 45
4-2-2-3機械性質測試 45

第五章 結論 63
5-1擠型材LZ91、FSP-LZ91及FSP-LZ91經冷軋延 63
5-2熱軋材LAZ941、FSP-LAZ941及FSP-LAZ941經冷軋延 63

參考文獻 65

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