Modeling the Effect of Excess Vacancies on Precipitation and Mechanical Properties of Al–Mg–Si Alloys

Abstract

A model for vacancy annihilation during aging has been combined with a precipitation model for coupled nucleation, growth, and coarsening in AA 6xxx series aluminum alloys. The simulation results were compared with precipitation parameters from TEM measurements and hardness data obtained for various times during artificial aging. Both simulations and measurements indicated that a combination of an excess concentration of non-equilibrium vacancies at the start of aging and a fast vacancy annihilation rate significantly affected the resulting precipitation and strength evolution. Hence, the model reproduced the short aging time required to reach the maximum strength when direct artificial aging was applied (DAA). In contrast to the fast aging response of DAA, the hardness measurements showed a much slower aging response when artificial aging was performed after prolonged natural aging. This aging behavior was captured in the model simulations by assuming that an equilibrium vacancy concentration is present from the start of the aging.