Predictive calculation of phase formation in Al-rich Al–Zn–Mg–Cu–Sc–Zr alloys using a thermodynamic Mg-alloy database

Abstract

Three series of Al-rich alloys in the system Al–Zn–Mg–Cu–Sc–Zr and the subsystems Al–Zn–Mg–Cu–Sc and Al–Zn–Mg–Sc were studied by thermodynamic calculations. Phase formation was compared with experimental data obtained by DTA and microstructural analysis. Calculated phase diagrams, phase amount charts and enthalpy charts together with non-equilibrium calculations under Scheil conditions reveal significant details of the complex phase formation. This enables consistent and correct interpretation of thermal analysis data. Especially the interpretation of liquidus temperature and primary phase is prone to be wrong without using this tool of computational thermodynamics. All data are predictions from a thermodynamic database developed for Mg-alloys and not a specialized Al-alloy database. That provides support for a reasonable application of this database for advanced Mg-alloys beyond the conventional composition ranges.