Investigation On The Phase Diagram And Thermodynamics Of The Al-Cu-Sc-Si System

CALPHAD (CALculation of PHAse Diagram) technique is an effective and widely utilized method for assessment and calculation of multicomponent materials. To effectively improve the performance of aluminum alloy, design alloy’s composition and optimize the synthesis process, an accurate knowledge of the phase diagram and thermodynamics of the multi-component Al-based system is needed. This work focused on Al-Cu-Sc-Si system using CALPHAD technique, key experiment and the first-principle calculation. Firstly, this work critically assess the six binary systems (Al-Cu, Al-Sc, Al-Si, Cu-Sc, Cu-Si, Sc-Si) and four ternary systems (Al-Sc-Si, Al-Cu-Si, Cu-Sc-Si, Al-Cu-Si). Then, based on the optimized parameters of these binary systems and ternary systems, the database of the quaternary Al-Cu-Sc-Si system is established.The main reseach results obtained in this work are shown as follows:(1) The heat contents of Sc5Si3and ScSi in the Sc-Si system were measured using drop calorimeter method. Thermodynamic optimization of the Sc-Si system was performed with the present experimental data and data from the literature. A set of self-consistent thermodynamic parameters for the Sc-Si system was obtained.(2) The phase relationship and phase transition temperature in the Al-rich corner of the Al-Sc-Si system had been determined in this work by means of XRD, EPMA and DTA. Based on the experimental data in the literature and in this work, the Al-Sc-Si system was optimized using the CALPHAD method and a set of self-consistent thermodynamic parameters for the Al-Sc-Si system was obtained.(3) The Cu-Sc system was reoptimized in this work. Based on the experimental data in the literature and the enthalpies of formation of the ternary compounds by first-principles calculations, a set of self-consistent thermodynamic parameters for the Cu-Sc-Si system was obtained.(4) Based on the thermodynamic parameters of Al-Cu-Sc、Al-Cu-Si、 Al-Sc-Si and Cu-Sc-Si systems, the database of the quaternary Al-Cu-Sc-Si system was established.