Thermodynamics of liquid and undercooled liquid Al–Cu–Ni–Si alloys

Abstract

The partial and the integral enthalpies of mixing of liquid Al–Cu–Ni–Si alloys have been determined by high temperature isoperibolic calorimetry for four isopleths at 1575±3 K. A least-square regression analysis of the data together with the literature values of the constituent binaries and ternaries results a consistent analytical representation of the enthalpy of mixing of liquid Al–Cu–Ni–Si alloys at 1575 K. The regular association model describes adequately the thermodynamic properties of the liquid constituent ternaries on the basis of their constituent binaries, respectively, if additional ternary association reactions with the stoichiometries Al 2Cu 1Ni 1, Al 1Cu 3Si 1, Al 1Ni 2Si 1, and Cu 2Ni 2Si 1 are assumed. The calculated Gibbs energy for the ternaries demonstrate that there are minima for the Al–Cu–Ni (−42.8 kJ mol −1), Al–Ni–Si (−54.6 kJ mol −1), Al–Cu–Si (−24.4 kJ mol −1) near the ternary compositions Al 0.45Cu 0.10Ni 0.45, Al 0.20Ni 0.55Si 0.25, and Al 0.17Cu 0.50Si 0.33, respectively, whereas the minimum for the liquid Cu–Ni–Si alloys (−52.0 kJ mol −1) corresponds to the binary composition Ni 0.58Si 0.42. The Gibbs energy of liquid quaternary alloys were estimated on the basis of the results from the regular association model for the constituent ternaries using the Kohler scheme in combination with an empirical enthalpy–entropy model. The minimum of the Gibbs energy of mixing of the quaternary alloys is observed at the composition Al 0.19Cu 0.08Ni 0.50Si 0.23.