| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 101 === 6061-T6 aluminum alloy has been used extensively as structural materials for internals of experimental nuclear reactors, aircraft fittings, amour systems and high-speed machinery for years due to its superior mechanical properties. In this study, the high temperature deformation and micro-structural evolution of 6061-T6 aluminum alloy under high strain rate loading condition are investigated by means of a split-Hopkinson bar. The specimens with longitudinal direction are heated using a clam-shell radiant-heating furnace. Impact tests are performed at strain rate ranging from 1×103 to 5×103 s-1 and temperatures between 100℃ and 350℃. The experimental results indicate that the flow response of 6061-T6 aluminum alloy is related to temperature and strain rate. At a constant temperature, plastic stress, work hardening rate and strain rate sensitivity all increase with the increasing strain rate, while the thermal activation volume decreases.
However, at a constant strain rate, plastic stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, while the thermal activation volume increases. The observed that high temperature and high strain rate deformation behavior of 6061-T6 aluminum alloy can be adequately described using the Zerilli-Armstrong constitutive equation. Transmission electron microscopy observations reveal that the dislocation density increases with an increasing strain rate, but decreases with an increasing temperature. The strengthening effect observed at higher strain rates and lower temperatures is attributed to a greater dislocation density. The stacking fault is also found in high temperature and high strain rate. A linear relationship between the square root of the dislocation density and the true stress is also found.
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