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A. Redermeier, T. Wojcik, T. Ebner, E. Kozeschnik:
"Evolution of meta-stable phases in Al-Mg-Si alloys - Comparison of thermokinetic simulations and experimental findings";
Talk: Euromat 2019, Stockholm; 2019-09-01 - 2019-09-05.

Introduction / Purpose:
Ecological reasoning demands for the use of light weight materials in transportation. For this purpose, especially the Al-Mg-Si alloys, are an interesting candidate due to their good corrosion resistance, hardness and good castability. During heat treatment, these alloys undergo a complex precipitation sequence of various metastable phases. A profound understanding of the precipitation sequence is essential to predict material properties like tensile strength.
In this study, we use thermokinetic simulations to reproduce not only differential scanning calorimetry (DSC) curves but also number densities and type of metastable precipitates for different ageing times for two high purity Al-Mg-Si alloys.
Methods:
Thermokinetic software packages are based on two cornerstones, namely CALPHAD type databases and thermokinetic models. CALPHAD type databases provide information on the Gibbs energy of all occurring thermodynamic phases as function of chemical composition and temperature. Moreover, diffusion properties are available with these databases. Thermokinetic models describe the evolution of precipitates as function of chemical composition, temperature and strain.
For this work, we use the software package MatCalc, which is based on a mean-field treatment of nucleation, growth and coarsening of multi-component and multi-phase systems. The thermodynamic databases are developed in-house.
To reproduce the DSC-curves, we carefully select the important thermokinetic models and adjust the parameters accordingly. With these settings and parameters, we simulate the evolution of precipitates for different chemical compositions and different ageing times.
Results:
The simulated DSC curves are qualitatively in good agreement with the measured ones. Our thermokinetic simulations reproduce well the experimental findings for number densities and type of precipitates for both alloys.
Conclusions:
The thermokinetic simulation of DSC-curves reveals a deeper understanding of the complex precipitation sequence in Al-Mg-Si alloys. The parameter set, calibrated to the simulation of DSC-curves is also valid for the prediction of the precipitate evolution for different chemical compositions and varying ageing conditions.