臺灣博碩士論文加值系統

本研究係利用壓縮式霍普金森高速撞擊試驗機(Split Hopkinson pressure bar)及溫度調控裝置，探討在不同溫度及應變速率下AZ80鎂合金之撞擊特性與微觀結構。圓柱形試片於實驗溫度-100℃、25℃及300℃，及應變速率800s-1、1500s-1、2200s-1條件下進行測試，以分析溫度以及應變速率對鎂合金塑變行為與微觀結構之影響。
實驗結果顯示，溫度和應變速率對AZ80鎂合金之機械性質影響甚巨。在相同溫度條件下，其塑流應力值、加工硬化率，應變速率敏感性係數及溫度敏感性係數均會隨應變速率之增加而上升，而熱活化體積及活化能則會下降。相反地，在相同應變速率條件下，其塑流應力值、加工硬化率、應變速率敏感性係數及溫度敏感性係數隨溫度之增加而下降，而熱活化體積以及活化能則會上升。此外，藉由Zerilli-Armstrong構成方程式，來準確的預測AZ80鎂合金在不同溫度及應變速率下的塑變行為。
在微觀方面，由光學顯微鏡之觀測可知AZ80鎂合金在高速荷載下產生滑移變形，且受溫度與應變速率影響，晶相形貌及相組成體積百分比亦隨之改變；在掃描式電子顯微鏡之觀察結果顯示，肇因於此合金為HCP晶格結構，其破斷面為脆性破壞，而隨著β相提升，破斷面之韌性破壞會隨之提升；另在穿透式電子顯微鏡下則可觀測到差排密度隨著應變速率上升和溫度降低而隨之增加，差排密度的平方根與塑流應力值作線性關係上升。最後結合巨觀機械性質與微觀結構結果證實了差排密度、塑流應力值、應變速率敏感性係數及熱活化體積有重要的相關性。

In this study, a spit-Hopkinson bar is utilized to investigate the effect of temperature and strain rate on impact response and microstructural characteristics of AZ80 magnesium alloy at different temperatures of -100℃, 25℃and 300℃, under strain rates of 800s-1,1500s-1 and 2200s-1, respectively.
The experimental results indicate that the mechanical properties are related to temperature and strain rate. At a constant temperature, flow stress, work hardening rate, strain rate sensitivity and temperature sensitivity all increase with the increasing strain rate, while the thermal activation volume and activation energy decreases. However, at a constant strain rate, flow stress, work hardening rate, strain rate sensitivity, and temperature sensitivity decrease with increasing temperature, while the thermal activation volume and activation energy increases. In addition, the observed impact deformation behavior of AZ80 magnesium alloy under current testing conditions can be described by the Zerilli-Armstrong equation.
Optical microstructural observations reveal that the formation of slip band and morphology of deformed grain of Z80 magnesium alloy are strongly dependent on temperature and strain rate. The SEM fracture analysis results indicate that due to the presence of HCP structure, the fracture surfaces of the deformed AZ80 magnesium specimens are dominated by cleavage feature. However, the ductile fracture is found to increase with increasing β phase. TEM observations show that the dislocation density increases with increasing strain rate, but decreases with increasing temperature. A linear relationship between the flow stress and square root dislocation density is observed. Finally, the flow stress, strain rate sensitivity and thermal activation volume are related to the observed dislocation substructure.

總目錄
中文摘要 I
Abstract II
Extended Abstract III
誌謝 IX
總目錄 X
表目錄 XIII
圖目錄 XIV
符號說明 XXII
第一章 前言 1
第二章理論文獻與回顧 3
2-1鎂及鎂合金之介紹 3
2-1-1鎂合金的分類 3
2-1-2鎂合金製造及加工性 4
2-1-3添加合金成分對鎂合金的影響 5
2-1-4鎂合金之熱處理強化機制 6
2-2AZ80鎂合金之介紹 7
2-2-1 AZ80鎂合金之熱處理方式 7
2-3塑性變形之機械測試類別 8
2-4 一維波傳理論 9
2-5霍普金森狀及試驗機原理 11
2-6材料塑變行為特性 13
2-7材料構成方程式 16
2-7-1 Ludwik model [15, 26, 27] 17
2-7-2 Sokolosky＆ Malvern model [15] 17
2-7-3 Vinh model[15, 28] 17
2-7-4 Duffy model [15] 17
2-7-5 Kobayashi ＆ Dodd model[29, 30] 18
2-7-6 Zerilli-Armstrong model [31, 32] 18
2-7-7 Johnson-Cook model [4, 34-36] 19
第三章 實驗方法及步驟 29
3-1實驗流程 29
3-2實驗儀器與設備 29
3-2-1 霍普金森撞擊試驗機 29
3-2-2實驗環境加熱裝置 31
3-2-3光學顯微鏡(OM) 31
3-2-4掃描式電子顯微鏡(SEM) 31
3-2-5聚焦離子束(FIB) 31
3-2-6穿透式電子顯微鏡(TEM) 32
3-3實驗步驟 32
3-3-1實驗材料試片製備 32
3-3-2 動態撞擊實驗 33
3-3-3金相組之觀察(OM) 33
3-3-4 破斷面之觀察(SEM) 34
3-3-5 TEM試片製備(FIB) 34
第四章 實驗結果與討論 39
4-1應力-應變曲線 39
4-2 加工硬化率 40
4-3 應變速率敏感性係數 42
4-4 熱活化體積 43
4-5 活化能 45
4-6 溫度敏感性係數 46
4-7 理論溫升量 47
4-8 材料構成方程式 48
4-9 光學顯微鏡(OM)金相組觀察 49
4-10 掃描式電子顯微鏡(SEM)破壞特徵分析 50
4-11 穿透式電子顯微鏡(TEM)差排結構特徵 51
第五章 結論 125
參考文獻 127

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