本文主要是探討6061-T6鋁合金在低溫下之撞擊特性與微觀結構分析。利用壓縮式霍普金森桿高速撞擊試驗機(Hopkinson bar)及低溫裝置，於應變速率分別為1000 s-1、3000 s-1和5000s-1；實驗環境溫度分別為-196℃、-100℃、0℃條件下測試，以分析溫度以及應變速率對材料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6061-T6鋁合金之機械性質影響甚巨。在相同溫度條件下，其塑流應力值與應變速率敏感性係數均會隨應變速率之增加而上升，而加工硬化率和熱活化體積則會下降。相反地，在相同應變速率條件下，其塑流應力值與應變速率敏感性係數則會隨溫度之增加而下降，而熱活化體積則會上升。此外，可以藉由Zerilli-Armstrong構成方程式，來準確的預測此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6061-T6鋁合金中有絕熱剪切帶形成及晶粒組織形貌的改變，兩者皆受溫度與應變速率的影響；然而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。最後結合巨觀與微觀結果證明了塑流應力值隨著差排密度的平方根作線性的增加趨勢，證實了Bailey-Hirsch關係式的存在，也證實了差排密度、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 study the effect of temperature and strain rate on impact response and microstructural characteristics of 6061-T6 aluminum alloy at different cryogenic temperatures of 0℃, -100℃and -196℃, under strain rates of 1000s-1, 3000s-1 and 5000s-1, respectively.
The experimental results indicate that the mechanical properties are related to temperature and strain rate. At a constant temperature, flow stress and strain rate sensitivity all increase with the increasing strain rate, while the work hardening and thermal activation volume decreases. However, at a constant strain rate, flow stress and strain rate sensitivity decrease with increasing temperature, while the thermal activation volume increases. In addition, the observed impact deformation behavior of this alloy under current testing conditions can be described by the Zerilli-Armstrong equation.
Optical microstructural observations reveal that the formation of adiabatic shear band and morphology of deformed grain of 6061-T6 aluminum alloy are strongly dependent on temperature and strain rate. Transmission electron microscopy (TEM) observations show that the dislocation density increases with increasing strain rate, but decreases with increasing temperature. Based on the experimental mechanical properties and microstructural characteristics, it is found that the correlation between the dislocation density and flow stress obeyed by the Bailey-Hirsch type relation. In addition, the flow stress, strain rate sensitivity and thermal activation volume are also related to the observed dislocation substructure.

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