Precipitation kinetics and crystal plasticity modeling of artificially aged AA6061

Abstract

An artificially aged AA6061 alloy was investigated at multiple heat treatment conditions with monotonic tensile and cyclic shear testing to characterize the effect of precipitation on the alloy's mechanical properties. The microstructure was first measured with scanning electron microscopy, which was observed to remain fairly constant throughout all aging conditions. Mechanical testing showed that artificial aging reduced the initial work hardening rate without affecting dynamic recovery. The alloy also exhibited a reduction in plastic anisotropy and an increase in kinematic hardening with increased aging time. Afterwards, a numerical through-process framework was introduced to predict both the precipitation kinetics and mechanical behavior of AA6000-series materials. The kinetics model was calibrated and validated with transmission electron microscopy measurements on several Al-Mg-Si alloys. The mechanical model uses the simulated precipitate distribution in a modified crystal plasticity framework to calculate the alloy's constitutive response. The framework was able to simulate the yield strength, work hardening, plastic anisotropy and Bauschinger behavior of AA6061 with reasonable accuracy. Plastic anisotropy and kinematic hardening was specifically captured with an inclusion-based method of modeling the precipitates. The model was later used to simulate precipitation hardening in individual single crystals. It was observed that the effect of artificial aging is minor compared to the overall effect of texture on the material.