本研究以7075鋁合金為實驗材料，探討不同方位取向、人工時效及預應變處理對共振破壞行為及裂縫傳播特徵的影響。
實驗結果顯示，不同方位取向的試片具裂縫傳播速率的差異。軋延方向試片其裂縫傳播速率最慢，導致其共振壽命較其它兩取向試片為佳。此外，三取向試片之主裂縫均以穿晶傳播為主。
在人工時效方面之共振測試結果顯示，在固定振動台出力值條件下，其起始偏移量由高至低依序為峰值時效、固溶化、初時效以及過時效，恰與共振壽命長短順序相反。亦即，等出力條件下試片之振動破壞阻抗與制振性成正比。而在固定試片末端起始偏移量條件下，共振壽命則隨著降伏強度增加而增加。另外，在裂縫傳播特徵方面，固溶化試片其主裂縫主要以穿晶、局部沿滑移帶傳播的方式成長；初時效、峰值時效及過時效試片並無觀察到滑移帶生成，其主裂縫傳播均以穿晶為主。固溶化及初時效試片其主裂縫遇到晶界不會改變傳播方向，但峰值時效及過時效試片，可觀察到主裂縫有遇到晶界而改變其傳播方向的情形。
另外，本研究亦發現，經展伸及峰值時效之7075合金(T651)，於固定振動台出力值下，其制振性及共振壽命均較上述各時效條件試片差，此結果顯示7075-T651鋁合金不適合應用於振動環境。

This study aims to explore the effects of sampling direction, artificial aging and stretch treatment on the resonant vibration properties of the commercial 7075 alloy. The influence of crack propagation characteristics on the vibration life was also investigated.
Experimental results indicate that different sampling direction caused the difference in crack propagation rate. The RD (rolling direction) samples which show the lowest crack growth rate exhibit the greatest vibration life. The crack propagation path of the specimens is almost transgranular regardless of the sampling direction.
The results also show that under constant force conditions the initial deflection in a decreasing order and the vibration life in an increasing order are the peak-aged (PA), solution-treated (ST), under-aged (UA) and over-aged (OA) specimens. That is, the specimen with a greater damping capacity possesses a higher vibration fracture resistance under constant-force conditions. On the other hand, under constant initial deflection conditions the vibration life is proportional to the yield strength of the specimen. In addition, the major cracks of the ST specimens propagate mainly transgranularly, and the crack growth along the persistent slip bands can also be observed occasionally. As for other samples, main crack propagates transgranularly but the slip band cracking feature is absent. Notably, grain boundaries don’t affected the growth of the major crack of the ST and UA specimens, but slightly change the propagation direction of the cracks of the PA and OA samples.
Worthy of notice is that, the vibration life of the 7075-T651 samples undergoing stretch and peak aging treatments possess a lower vibration life in comparison with aforementioned artificially aged samples without the pre-strain under constant force conditions. This result suggests that the stretched 7075 alloys are not suitable to be applied under the vibration environment.

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