Modelling of quench sensitivity and age hardening curves of aluminium alloysWednesday (06.11.2019) 14:15 - 14:35 Part of:
Quench sensitivity of aluminium alloys is closely related to the precipitation process taking place during quenching. To understand the quench sensitivity of an alloy, it is essential to understand its precipitation process. Precipitation is a diffusion-controlled process, which is made complicated by the so-called quenched-in vacancies. These vacancies form during the solution treatment, become “excess” when temperature goes down, and annihilate during the following cooling and ageing treatments, making diffusion a function of both temperature and time. The effect of quenched-in vacancies on diffusion has been considered in the kinetic models to realise the calculation of TTT/CCT diagrams for aluminium alloys. The kinetics models have been integrated with precipitation hardening models developed previously, which enables the quantification of quench sensitivity and age hardening behaviour of aluminium alloys. This integrated model allows the formation of stable precipitates during cooling, as a result of which the amount of solutes in the matrix is changed, affecting its hardening potential during ageing treatment, i.e. the so-called quench sensitivity. The formation and hardening of GP zones and their transition to metastable hardening phases have also been considered. The performance of this integrated model has been demonstrated against experimental data on heat treatment time, age hardening curve and quench sensitivity of a wide range of commercial aluminium alloys. Advantages and limitations of this integrated approach are discussed as well.