本研究將Al-5wt%Zn合金在室溫下以路徑Bc，通道交角為120°，經由等徑轉角擠型（equal channel angular extrusion, ECAE）擠製16道使晶粒細化至超細晶尺寸，來探討超細晶Al-Zn合金於不同溫度及應變速率下對拉伸變形行為的影響，並與Al-5wt%Zn相同製程條件之4N純鋁的拉伸變形行為做比較。
研究結果指出，隨著拉伸溫度增加，Al-5wt%Zn的延展性提升，在473 K溫度下總伸長量比在室溫298 K下高出65%，和相同擠製道次下4N純鋁相比主要提升量在於非均勻伸長量(post uniform elongation ,PUE) 的大幅提升，並且應變速率敏感值(strain rate sensitivity, m)也有明顯增加，試片表面也觀察出現許多裂縫及孔洞，是晶界滑移發生的證據。因此吾人推測Zn原子的添加，因為其容易在晶界上擴散而幫助晶界滑移(grain boundary sliding, GBS)，而晶界滑移應是造成PUE隨著溫度提升而增加的重要機制。
在低應變速率下，隨著溫度提升，晶界滑移更為明顯，延展性也隨之提升，以及應力應變曲線圖會出現降伏下降及動態應變時效的現象，而動態應變時效的發生會有效提升加工硬化率，進而提升延展性。
Al-5wt%Zn活化體積(activation volume, υ*)在不同溫度下範圍在21~41b3，推論影響超細晶Al-Zn差排移動的關鍵機制主要來自差排在晶界處與Zn原子之間的作用。

In this work, ultrafine-grained (UFG) Al-5wt%Zn alloy was produced by equal channel angular extrusion (ECAE) with 120 degree die. The tensile deformation behavior of this UFG Al-5wt%Zn alloy was investigated at temperatures ranging from 77 K to 473 K with various strain rates. In order to identify the effect of Zn in the Al-Zn alloy, pure aluminum (4N, 99.99%) was also studied for comparison.
The tensile elongation of the UFG Al-5wt%Zn alloy increases with increasing temperature. After the same ECAE processing, the UFG Al-5wt%Zn alloy possesses higher tensile strength and elongation than pure aluminum. The improved tensile elongation of the UFG Al-5wt%Zn alloy is mainly due to the contribution of post-uniform elongation (PUE), which can be related to increased strain rate sensitivity (SRS). Observations of the surface of tensile tested specimen revealed the evidence of grain boundary sliding (GBS) in the UFG Al-5wt% Zn alloy. It is proposed that the addition of Zn may enhance the grain boundary diffusion in the UFG Al-Zn alloy and facilitate the process of GBS. It is believed that the enhanced GBS is responsible for the increasing of PUE with increasing temperature. At low strain rates, 1- 4 x 10-5s-1, the UFG Al-5wt% Zn alloy exhibits yield phenomenon and dynamic strain aging at 373 K - 423 K, which result in increased work-hardening rate and tensile elongation.
The activation volume (v*) of the UFG Al-Zn alloy is in the range of 21b3~41b3 for the temperature range studied. Based on the small value of the activation volume, it is suggested that the controlling mechanism for tensile deformation in the UFG Al-Zn alloy might be related to the generation and absorption of dislocations in grain boundary, which is affected by the interaction between dislocations and Zn atoms in the grain boundary.

論文審定書 i
致謝 ii
摘要 iii
Abstract iv
表目錄 vii
圖目錄 viii
一、前言 1
二、文獻回顧 2
2-1等徑轉角擠型(equal-channel angular extrusion, ECAE) 2
2-2影響ECAE 之製程參數 2
2-2-1對於模角的影響 2
2-2-2 路徑的影響 3
2-3超細晶金屬之機械性質 3
2-3-1 超細晶金屬的強度 3
2-3-2超細晶金屬的延展性 4
2-3-3 超細晶金屬之拉伸變形行為 5
2-4超細晶金屬的應變速率敏感值 6
2-5Al-Zn合金之介紹 8
2-5超細晶Al-Zn合金 8
三、實驗方法 10
3-1 實驗材料 10
3-2均質化處理 (Homogenization) 10
3-3等徑轉角擠型 (ECAE) 10
3-4拉伸前微結構分析 10
3-5電子背向散射繞射(EBSD)分析 11
3-6拉伸性質測試 11
3-7變形表面型態觀察 12
四、實驗結果 13
4-1拉伸前微結構觀察 13
4-2拉伸性質 13
4-2-1不同溫度下之拉伸性質比較 13
4-2-2 4N 純鋁在不同溫度下的拉伸性質 15
4-2-3不同拉伸速率下之拉伸性質比 16
4-2-4拉伸後試片表面觀察 17
4-3應變速率敏感值(strain rate sensitivity)測試 19
4-3-1不同測試溫度下之應變速率敏感值測試 19
5-5-2 4N純鋁、Al-5wt%Zn和Al-15wt%Zn[2]之拉伸性質比較 20
五、討論 21
5-1測試溫度對拉伸性質的影響 21
5-2應變速率對拉伸性質的影響 22
5-3測試溫度對Al-5wt%Zn應變速率敏感值與活化體積的影響 23
5-3-1 應變速率敏感值 23
5-3-2 活化體積 24
六、結論 27
參考文獻 28

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