鋁合金在高應變率下應力應變結果之穩定性

本文採用兩種常用的鋁合金材料：Al2024-T351和Al7075-T6作成試片，利用MTS材料試驗機進行單軸向應力之壓縮試驗。實驗的溫度範圍為常溫至300℃，平均應變率為100 以上，屬高應變率試驗。再藉真實應力應變曲線對應力應變穩定性作探討與解釋。實驗結果顯示，材料的流動應力曲線圖的趨勢由加工硬化與加工軟化的效果來決定。加工軟化的機構主要為動態回復與動態再結晶。在再結晶溫度附近的溫度範圍內，溫度的影響與應變率的溫升效應影響相當，所以降伏應力的變化較大。在低溫時影響流動應力曲線主要是應變硬化與動態回復。溫度再高時，動態再結晶的影響會越顯著。在遠高於再結晶溫度的情況下，材料已經過再結晶或晶粒成長完成，應變硬化的效果已不明顯。實驗中可發現Al2024-T351其主要滑移系統大量滑移，在試片內部形成圓錐狀的剪變形帶。低溫時造成試片巨觀上的破裂，高溫時在圓截面上形成環形帶狀的組織。故由此可證明剪變形帶與材料的破裂形式有關。關鍵字:高應變率、動態回復、動態再結晶、加工硬化

關鍵字

加工硬化；動態回復；高應變率

並列摘要

Two common aluminum alloys, namely ,　Al2024-T351 and Al7075-T6 are adopted as the specimen materials. We operated an uniaxial-stress compression test on the Material Testing System, at temperatures ranging from 20℃ to 350℃ and at average true-strain rates greater than 100. The experiment results show that the trend of the flow stresses of materials depends on the effects of work-hardening and work-softening. Dynamic recovery and dynamic recrystallization were the chief mechanisms of work-softening. At temperatures near the recrystallization temperatures of the alloys, the effect of temperature was equivalent to that of strain-rate. On the trend of flow stress, the variation of yield stress is obvious. When the test temperature was lower than recrystallization temperature, work-hardening and dynamic recovery are the main mechanisms that affect the trend of flow stresses. At higher temperature, dynamic recrystallization dominates over dynamic recovery . At temperatures that was much higher than the recrystalliization temperature, the alloys have undergone recrystallization and grain growth. The yield stress increased with strain-rate increasing, but the phenomenon of strain-hardening became undefined. When Al2024-T351 was subjected to high-strain-rate deformation, the principle slip system formed a cone–like shear band. Macroscopic fracture occurs at the edges of shear bands at low temperature. Key words：high-strain-rate、dynamic recovery、dynamic 　　　　 recrystallization、

並列關鍵字

high-strain-rate ； work-hardening ； dynamic recrystallization ； dynamic recovery

參考文獻

high strain rate compression of 2024 T351 Aluminum , J.Mater. Sci.,23(1988),p.3578-3587

modeling of the high temperature flow behavior of

aluminum alloy 2024,metallurgical transaction

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國際替代計量

鋁合金在高應變率下應力應變結果之穩定性

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