Abstract
A new numerical modelling approach integrating the Langer and Schwartz approach and log-normal particle size distribution has been developed to depict the precipitation kinetics of age-hardening precipitates in Al alloys. The modelling framework has been implemented to predict the precipitation behavior of the key secondary phases in 6xxx and 7xxx Al alloys subjected to artificial aging. The simulation results are in good agreement with the available experimental data in terms of precipitate number density, radius, and volume fraction. The initial shape parameter of the log-normal size distribution entering the modeling framework turns to play an important role in affecting the later-stage evolution of precipitation. It is revealed that the evolution of size distribution is not significant when a small shape parameter is adopted in the modelling, while an initial large shape parameter will cause substantial broadening of the particle size distribution during aging. Regardless of the magnitude of shape parameter, a broadening of the particle size distribution as predicted by the present model is in agreement with experimental observations. It is also shown that large shape parameter will accelerate the coarsening rate at later aging stage, which induces fast decreasing of number density and increased growth rate of mean/critical radius. A comparison to the Euler-like multi-class approach demonstrates that the integration of more realistic log-normal distribution and Langer and Schwartz model make the present modelling faster and equivalently accurate in precipitation prediction.
Highlights
We present a revised Langer-Schwartz (RLS) model, which integrates the LS approach and log-normal particle size distribution to depict the precipitation kinetics including nucleation, growth and coarsening
A novel model termed as RLS approach which couples the Langer and Schwartz approach and log-normal particle size distribution has been developed to predict the precipitation behavior of the key precipitates including b¢¢, b¢, g¢ in 6xxx and 7xxx Al alloys subjected to artificial aging
The available transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) data concerning the precipitation of these secondary phases in terms of number density, mean radius, and volume fraction can be well predicted by the RLS approach
Summary
4838—VOLUME 51A, SEPTEMBER 2020 precipitation behavior of secondary phases during age-hardening process.[8,9,12,13,14,15,16,17,18,19,20,21,22,23,24,25] Based on the classical nucleation and growth theories, these models are able to predict the time evolution of the precipitation of secondary phases during heat treatment. A detailed comparison between the mean size and multi-class approaches conducted by Perez et al.[19] reveals that in simple cases, the ‘‘mean size approach’’ is faster and as accurate as the multi-class approaches in predicting the general course of precipitation: nucleation, growth, coarsening. This suggests that the ‘‘mean size approach’’ is able to predict accurate results in the modeling framework wherein an implementation of KWN multi-class approach is not computationally affordable.
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