Experimental investigation and thermodynamic assessment of the Al–Ag–Sc system

As an important system in heat-resistant aluminium alloys, Al–Ag–Sc still has no publication on the investigation of thermodynamics and phase equilibria. In the present work, the isothermal sections of the Al–Ag–Sc ternary system at 500 and 600 ºC were experimentally measured through electron probe microanalysis (EPMA) and X-ray diffraction (XRD) for alloy samples. The ternary maximum solubility of Al in AgSc, Ag 2 Sc, Ag 4 Sc, and Ag in Al 3 Sc are 20.5 ± 0.5, 5.2 ± 0.3, 6.3 ± 0.2 and 12.5 ± 0.3 at. %, respectively. In addition, two stable ternary compounds Al 36 Sc 36 Ag 28 and Al 27 Sc 18 Ag 55 were newly discovered. The solidification paths were measured for as-cast alloys. Five primary phases AgSc, (Ag), Ag 2 AlSc, Al 36 Sc 36 Ag 28 and Al 3 Sc were revealed. The end-members formation enthalpies of the Al–Ag–Sc intermetallic compounds were computed by first-principles calculations. Based on the experimental and first-principles calculations results, a set of thermodynamic parameters for the Al–Ag–Sc system were established by the application of the CALPHAD (CALculation of PHAse Diagrams) method. The phase equilibrium, isothermal section, liquidus projection and solidification structure are well reproduced by using the thermodynamic parameters obtained in this work. • The maximum solubility of Al in AgSc, Ag 2 Sc, Ag 4 Sc and Ag in Al 3 Sc were measured. • Two stable ternary phases Al 36 Sc 36 Ag 28 and Al 27 Sc 18 Ag 55 were newly discovered. • The isothermal sections of Al–Ag–Sc at 500 and 600 °C were determined through experimentation and extrapolation. • Five primary phases were experimentally revealed. The liquidus projection and solidification paths in the Al–Ag–Sc system were determined. • A set of thermodynamic parameters for the Al–Ag–Sc system were assessed for the design of Al alloys.