Aluminum microstructure evolution and effects on mechanical properties in quenching and aging process
High strength aluminum alloy is recently widely applied in aircraft, automobile and construction industry fields. Typical T6 heat treatment process can be applied to improve the heat treatable aluminum alloy in order to facilitate the formation of prime strengthening precipitate phases. Critical steps in T6 heat treatment process include solution treatment, quenching and aging. Due to high thermal gradient variants in quenching process and aging process, large thermal stress will remain in the matrix and bring unexpected deformation or distortion in further machining. Therefore, in order to predict and minimize the thermal stress effects, a proper constitutive model and precipitate hardening model are needed to describe the mechanical properties of aluminum alloy.
In this dissertation, an optimized constitutive model, which is used to describe the mechanical behaviors in quenching and intermediate period of quenching and aging process, was given based on constitutive models with Zenor-Holloman parameter. Modification for constitutive model is based on the microstructure model both developed for quenching and aging processes. Quench factor analysis method was applied to describe the microstructure evolution and volume fraction of primary precipitate phases during quenching process. Some experimental phenomena are discussed and explained by precipitates distributions. Classical precipitate hardening models were reviewed and two models were selected for Al-Cu-Mn alloy aging treatment. Thermal growth model and Euler algorithm were used to improve the accuracy and the selected precipitate hardening models were validated by yield stress and microstructure observations of Al-Cu-Mn aging response experiments.