臺灣博碩士論文加值系統

本研究乃對於6061-T6鋁合金垂直於滾軋板材方向(Transverse) 於高溫及高應變速率下之不同溫度、不同應變速率荷載下之巨觀機械性質及微觀結構變化之分析與討論。主要利用霍普金森高速撞擊試驗機及高溫加熱裝置，材料於100 ℃、200 ℃與350 ℃，及應變速率分別為1000 s^(-1)、3000 s^(-1)與5000 s^(-1)條件下進行高速撞擊，以探討溫度及應變速率相對於材料之塑變行為及微觀結構之影響。
結果顯示，相同溫度條件，其塑流應力值、加工硬化率及應變速率敏感性係數均隨應變速率增加而增加，而熱活化體積則會下降。反之，相同應變速率條件下，其塑流應力值、加工硬化率及應變速率敏感性係數均隨溫度增加而下降，而熱活化體積則會上升。此外，可以藉由Zerilli-Armstrong構成方程式，準確描述此合金在不同溫度及應變速率下的動態塑變行為。
微觀結果方面，由光學式顯微鏡之觀測可知6061-T6合金於高溫高應變速率下有再結晶的出現且晶粒組織形貌也有所改變，而晶粒細化與再結晶為材料於高溫、高應變速率下強度改變的原因。而在穿透式電子顯微鏡下則可觀察到差排密度隨著應變速率上升而增加，隨溫度上升而減少，且可於高溫低應變速率時發現疊差缺陷與魏氏組織的產生。再藉由差排密度、差排環尺寸、塑流應力值、應變速率敏感性係數及熱活化體積之連結並導入Modified Hall-Petch relationship，解析巨觀機械性質與微觀結構之相依性。最後導入疊差缺陷能公式，對微觀結構變化作一完整說明。

In this study, the effect of temperature and strain rate on plastic deformation and microstructure of 6061-T6 aluminum with Transverse direction is evaluated. A split Hopkinson pressure bar tester is utilized to investigate the macro-mechanical properties and microstructural variation of the specimens under high strain-rate loadings over wide temperature range. The specimens are deformed at 100 ℃, 200 ℃ and 350 ℃ under the strain rates of 1000 s^(-1), 3000 s^(-1) and 5000 s^(-1).
The experimental results indicate that the mechanical properties are related to temperature, strain rate and strain. At a constant temperature, plastic stress, work hardening rate and strain rate sensitivity all increase with the increasing strain rate, while the thermal activation volume decreases. However, at a constant strain rate, plastic stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, while the thermal activation volume increases. A Zerilli-Armstrong constitutive equation is used to predict flow behavior under different temperatures and strain rates.
OM observation results indicate that the morphology of deformed grain and recrystallization varied with strain rate and temperature. Moreover, grain refinement and recrystallization are observed of influencing largely intensity at high temperature and high strain rate. TEM microstructure observations reveal that the dislocation density increases with the increasing strain rate, but decreases with the increasing temperature. In addition, stacking defects and Widmanstatten structure generate at high temperature and low strain rate. The higher dislocation density prompts a reduction in the dislocation cell size. The relationship between flow shear, grain size and dislocation cell can be described by a modified Hall-Petch equation. Furthermore, the effect of grain size on the stacking fault energy is also evaluated.

1 中文摘要 I
2 ABSTRACT II
3 誌謝 III
4 總目錄 IV
5 表目錄 VII
6圖目錄 VIII
7 符號說明 XV
8第一章 前言 1
9第二章 理論與文獻回顧 3
2-1 鋁合金之介紹 3
2-2 6061-T6鋁合金之介紹 5
2-3 塑性變形之機械測試類別 5
2-4一維波傳理論 7
2-5霍普金森撞擊試驗機之理論基礎 9
2-6材料塑性變形行為 11
2-7材料構成方程式 15
10第三章 實驗方法及步驟 25
3-1實驗流程 25
3-2實驗儀器與設備 25
3-2-1動態機械性質測試系統：霍普金森撞擊試驗機 25
3-2-2光學顯微鏡(OM) 27
3-2-3穿透式電子顯微鏡(TEM) 28
3-2-4雙噴式電解拋光機 28
3-2-5低速切割機 28
3-2-6加熱裝置 29
3-3實驗步驟 29
3-3-1實驗試件製備 29
3-3-2動態衝擊實驗 29
3-3-3試件金相之觀察(OM) 31
3-3-4 TEM試片製備 31
11第四章 實驗結果與討論 34
4-1應力-應變曲線 34
4-2加工硬化率 35
4-3應變速率效應 36
4-4熱活化體積 37
4-5活化能 38
4-6 溫度效應 39
4-7理論溫升量 40
4-8材料組構方程式 41
4-9 OM金相組織觀察 42
4-10 TEM微觀結構分析 43
12第五章 結論 114
13參考文獻 117

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