A Microstructural Based Unified Model for Creep-Ageing Behaviour of Aluminium Alloy Under Various Thermal Conditions

A microstructure based constitutive analytical model considering the temperature effects on creep-ageing behavior of aluminium alloy has been developed. The evolution of precipitates for age hardening, as well as their interactions with dislocation evolution during creep have been considered and related equations have been proposed based on the nucleation and growth theory of precipitates for artificial ageing. These microstructures are then related to the yield strength and creep strain evolutions to update the strengthening and dislocation-based creep models, with which the temperature effects can be explicitly included. The analytical model has been successfully utilized to predict the microstructures (precipitation and dislocation) and macro properties (creep strain and yield strength) during creep ageing under different temperatures of an Al-Zn-Mg alloy. Furthermore, the capability of the developed model to predict the detailed creep and age hardening behaviour with complex multi-step heat treatment histories for creep-ageing processes has been presented and discussed with the same set of material constants. The analytical model developed in this study could be used to help the process design to achieve the concurrent optimization of accurate shape and high strength in the formed alloys.