Thermodynamic modeling and experimental investigation of the aluminum-copper-magnesium-zinc quaternary system

To establish a knowledge base for the development of high strength aluminum alloys, the Al-Cu-Mg-Zn quaternary system was thermodynamically modeled in the present study using the CALPHAD approach. In order to obtain a thermodynamic description for the Al-Cu-Mg-Zn quaternary system, it was necessary to first thermodynamically model the four constituent ternary systems, Al-Cu-Mg, Al-Mg-Zn, Al-Cu-Zn, and Cu-Mg-Zn. The thermodynamic descriptions of the ternary systems were developed based on the established descriptions of the constituent binary systems and the ternary experimental data available in the literature. Due to lack of experimental data, the quaternary description was obtained by extrapolating the ternary descriptions into quaternary space. Nevertheless, there are good agreement between the calculated phase equilibria and experimental data available in the Al-rich corner, which indicates that the quaternary description obtained in this study is reasonable. The phase equilibria and thermodynamic properties of the Al-Cu-Mg-Zn system can now be calculated from the thermodynamic description at any temperature and composition. The calculated phase equilibria in the Al-rich corner are believed to be reliable for engineering applications; those away from the Al-rich region are believed to be topologically correct and can be used as a guide for alloy design and processing development. Moreover, by integrating the thermodynamic description with kinetic models, the solidification paths of commercial Al-Cu-Mg-Zn alloys can be predicted by calculations at both equilibrium and non-equilibrium conditions.; In order to verify the reliability of the extrapolation approach used in the thermodynamic modeling, the equilibria between the liquid phase and the primary (Al) phase in the Al-Cu, Al-Cu-Mg and Al-Cu-Mg-Zn systems were experimentally investigated at 550{dollar}spcirc{dollar}C, 575{dollar}spcirc{dollar}C and 600{dollar}spcirc{dollar}C using Electron Probe Microanalysis. In view of the experimental uncertainties, the calculated phase equilibria are in good agreement with the experimental data. The agreement achieved between calculation and experimentation confirmed that the extrapolation approach used to obtain the thermodynamic description for the Al-Cu-Mg-Zn quaternary system is reasonable and the calculated phase equilibria in the Al-rich region are reliable for engineering applications.