Microstructure evolution during homogenization of Al-Mg-Si-Mn-Fe alloys: Modelling and experimental results

Microstructure evolution during the homogenization heat treatment of an Al-Mg-Si-Fe-Mn (AA6xxx) alloy was investigated using a combination of modelling and experimental studies. The model is based on the CALPHAD-coupled homogenization heat treatment model originally developed for AA3xxx alloys (i.e., Al-Mn-Fe-Si). In this work, the model was adapted to the more complex AA6xxx system (Al-Mg-Si-Mn-Fe) to predict the evolution of critical microstructural features such as the spatial distribution of solute, the type and fraction of constituent particles and dispersoid number density and size distribution. Experiments were also conducted using three direct chill (DC) cast AA6xxx alloys with different Mn levels subjected to various homogenization treatments. The resulting microstructures were characterized using a range of techniques including scanning electron microscopy, electron microprobe analysis (EPMA), XRD, and electrical resistivity measurements. The model predictions were compared with the experimental measurements, and reasonable agreement was found.