Mechanisms controlling the artificial aging of Al–Mg–Si Alloys

In this study the artificial aging behavior of the Al–Mg–Si alloy AA 6061 was investigated in the temperature range 150–250 °C using atom probe tomography, hardness and resistivity measurements for various thermal histories. It was found that the precipitation kinetics and age-hardening response of artificial aging at temperatures below 210 °C are lowered by prior natural aging but enhanced above this temperature. An analysis of hardness data was used to evaluate the temperature dependence of precipitation kinetics and dissolution processes. Supported by theoretical considerations, it is assumed that artificial aging of Al–Mg–Si alloys is controlled via the concentration of mobile vacancies. The “vacancy-prison mechanism” proposed determines the mobile vacancy concentration in the case of natural pre-aging by temperature-dependent dissolution of co-clusters and solute–vacancy interactions.

► Artificial aging of Al–Mg–Si alloys in the range of 150 and 250 °C.
► We study precipitation kinetics caused by various thermal histories.
► Natural pre-aging affects kinetics at low artificial aging temperatures.
► Natural pre-aging promotes kinetics at high artificial aging temperatures.
► A vacancy-prison mechanism explains the effect of natural pre-aging.