| Summary: | 碩士 === 義守大學 === 材料科學與工程學系 === 90 === Plastic instability is observed during stress rate change test of aluminum-magnesium alloy 5052 at room temperature. TEM observations reveal the microstructure and dislocation morphology of specimens at different final stress level and retention time.
In the stress rate change tests, strain retardation and plastic deformation instability are observed. During the stress rate change test, plastic strain is insignificant until the plastic instability occurs. If there is no unstable phenomena, the plastic strain rate would practically have no changes from beginning to end. The occurrence of plastic instability is related to the applied stress rate and retention time. By the argument of dynamic strain ageing effect, the plastic instability could be justified as the interaction between solid solution element, magnesium, and dislocations.
In order to modeling the plastic deformation mechanisms, thermally activated kinetic flow theory coupled with structural evolution law has been employed. Numerical methods of these coupled nonlinear equations are utilized. By changing the values of suitable parameters to simulate the microstructure change of instability, plastic instability could be modeled. Excellent agreement between numerical simulations and experimental data is observed.
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