Modeling the Influence of Cooling Rate on the Precipitate Evolution in Al-Mg-Si (Cu) Alloys

Abstract

The present study aims at understanding the process of age hardening in Al-Mg-Si (Cu) alloys, which starts immediately after annealing heat treatment followed by quenching. The cooling rate turns out to be one of the most important parameters in this process, since it will determine the quantity of quenched-in vacancies. During room temperature aging, these excess vacancies increase the diffusivity of alloying elements and accelerate the formation of precipitates until they become annihilated at available sinks. Using a model describing the role of parameters like quenching temperature, quenching rate and vacancy sink density, which are implemented in the thermo-kinetic software MatCalc, simulations are performed for 30 K/s to 1 K/s cooling conditions. Number density and size distribution of the complex sequence of precipitates are simulated and the tendencies are analyzed based on quantity and evolution of quenched-in vacancies. The model is validated by comparison with experimental data obtained from Vickers hardness measurements. no referenc to 6061.