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.

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