Effect of 0.3% Sc on microstructure, phase composition and hardening of Al-Ca-Si eutectic alloys

The phase composition, microstructure and hardening of aluminum-based experimental alloys containing 0.3% Sc, 0-14% Si and 0-10% Ca (mass fraction) were studied. The experimental study (electron microscopy, thermal analysis and hardness measurements) was combined with Thermo-Calc software simulation for the optimization of the alloy composition. It was determined that the maximum hardening corresponded to the annealing at 300-350 °C, which was due to the precipitation of Al3Sc nanoparticles with their further coarsening. The alloys falling into the phase region (Al)+Al4Ca+Al2Si2Ca have demonstrated a significant hardening effect. The ternary eutectic (Al)+Al4Ca+Al2Si2Ca had a much finer microstructure as compared to the Al-Si eutectic, which suggests a possibility of reaching higher mechanical properties as compared to commercial alloys of the A356 type. Unlike commercial alloys of the A356 type, the model alloy does not require quenching, as hardening particles are formed in the course of annealing of castings.