Integrated approach to thermodynamics, phase relations, liquid densities and microstructures in the Al-Bi-Cu system

Al-Bi-Cu phase equilibria were studied using, dedicated thermal analysis and microstructural investigation of slowly solidified samples. Experimentation in the most decisive Cu-rich region was enabled by developing a BN insert in combination with Ta-encapsulation for these challenging samples. A consistent thermodynamic model of the Al-Bi-Cu system is developed for the first time and applied to calculations of the entire phase diagram. The liquid miscibility gap of Al-Bi alloys extends dramatically upon addition of Cu. The density difference of the two liquids was determined in dedicated experimentation on buoyancy forces. The useful composition and temperature range for these experiments in the ternary L' + L '' region was provided by the thermodynamic calculations. The density data can be well interpreted on the basis of presently calculated coexisting liquid phase compositions. Finally, distinct ternary monotectic features on solidification microstructures of Al-Bi-Cu alloys are revealed and inter-related with the phase formation from thermodynamic calculations.