Thermodynamic modeling and experimental investigation of the aluminum-iron-magnesium-silicon quaternary alloy system

To establish a knowledge base for the development of high performance aluminum alloys, a thermodynamic description was developed in this study for aluminum alloys that include magnesium, silicon, and iron. Because of the complexity of this system, the establishment of the phase equilibria and thermodynamic properties of the entire quaternary system by experimental study alone would require an impracticably large amount of work. Instead, a phenomenological extrapolation technique was used to predict the phase equilibria and thermodynamic properties of higher-order systems based on those of the subsystems. First, thermodynamic databases were developed for three constituent ternary systems, Al-Fe-Mg, Al-Mg-Si, and Fe-Mg-Si based on established descriptions of the constituent binary systems and the ternary experimental data available in the literature. Next, these ternary systems were combined with the established Al-Fe-Si system and quaternary experimental data to create a thermodynamic description for the Al-Fe-Mg-Si system, which can be used to calculate the phase equilibria and thermodynamic properties of the Al-Fe-Mg-Si system at any temperature and composition. The thermodynamic description was used to analyze a real aluminum alloy, 6063. Solidification paths of aluminum alloy 6063 were simulated using the lever rule and the Scheil model. This simulation is in good agreement with experimental data from the literature.; in order to verify the reliability of the description, the equilibria between the liquid phase and solid phases were experimentally investigated in the Al-Fe, Al-Si, Al-Fe-Mg, Al-Mg-Si, and Al-Fe-Mg-Si alloy systems. Alloys of known composition were created from high-purity elements, brought to equilibrium at high temperature, and quenched. The compositions of the phases in equilibrium were measured using Electron Probe Microanalysis. The measured compositions are in good agreement with the calculated phase equilibria. This confirms that the thermodynamic description is reasonable and the calculations in the Al-rich region are reliable for engineering applications.