本文之研究主要是利用霍普金森撞擊試驗機，利用帽型試件(Hat Shaped)來探討三種不同鋁鈧合金在極高速動態剪切荷載下之絕熱剪切變形行為。實驗於室溫25℃，應變速率分別為3.0x105s-1~6.3x105s-1下進行，藉由實驗所得之巨觀機械性質與和微觀破壞機制，來探討以瞭解鋁鈧合金件在極高應變速率下的動態剪切特性及剪切帶微觀組織之變化。
實驗結果顯示，應變速率及應變量對鋁鈧合金的巨觀機械性質影響甚鉅，其塑流應力值隨著應變速率的增加而上升；在達到最大值後，因為熱軟化之影響，塑流應力隨著應變量的增加而下降。鋁鈧合金的應變速率敏感性係數隨應變速率上升而增加；隨應變量增加而減少。熱活化體積則隨著應變速率之增加而下降，隨應變量增加而增加。隨著應變量的增加，加工硬化率及應變速率敏感性皆呈現下降的趨勢，而熱活化體積則會上升。
微觀組織經由金相觀察後，發現三種鋁鈧合金的絕熱剪切帶均為變形剪切帶，且剪切帶寬度隨應變速率增加而減小。剪切帶中心的局部應變量最大，隨著離開剪切帶的距離增加局部應變量迅速減小。SEM破斷面分析發現三種鋁鈧合金破壞特徵為韌窩組織形貌，隨著應變速率增加，韌窩深度亦隨之增加。在三種鋁鈧合金的破斷面上並沒有觀察到任何的脆性劈裂形貌，顯示出這三種鋁鈧合金在極高速剪切荷載下仍然保持良好的塑變能力。

This study uses a compressive split-Hopkinson pressure bar with hat-shaped specimens to investigate adiabatic shear banding in three Al-Sc alloys tested at room temperature under extremely high strain rates ranging from 3.0×105s-1 to 6.5×105s-1. Optical microscopy (OM) and scanning electronic microscopy (SEM) techniques are used to analyze the shear band formation and the microstructural characteristics of the deformed specimens in order to establish the correlation between the adiabatic shear behaviour of the three Al-Sc alloys and their respective mechanical properties.
The experimental results indicate that the shear properties of the three alloys are significantly dependent upon the applied strain rate and strain. The shear flow stress, shear strain, strain rate sensitivity and temperature rise are all found to increase with increasing strain rate. Thermal softening takes place during the current adiabatic shear processes and has a significant effect on the dynamic shear mechanical properties of the Al-Sc alloys. Thermal softening results in strain instability and strain localization, and eventually leads to fracturing of the adiabatic shear band. The OM observations reveal that adiabatic shear bands are formed in all the impacted specimens. The local shear strain decreases with increasing distance from the center of the shear band, while the width of the shear band decreases with increasing strain rate. The SEM results reveal that the fracture surfaces of the three Al-Sc alloys are characterized by a dimple-like structure, which indicates that the specimens fail in a ductile manner. Furthermore, it is observed that the characteristic size of the dimples increases with increasing strain rate.
The results presented in this paper provide a useful reference for the application of the three Al-Sc alloys in high-speed plastic forming processes.

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