Abstract

The phase composition, structure and hardening of alloys in the aluminium corner of the Al–Ca–Sc system were studied in the range up to 10% Ca and up to 1% S≿. The experimental study (optical, scanning and transmission electron microscopy with electron-microprobe analysis, differential thermal analysis and hardness measurements) was combined with Thermo-Calc software simulation for the optimization of the alloy composition. It was shown that only phases of the binary systems (Al4Ca и Al3Sc) might be in equilibrium with the aluminium solid solution. It was shown that the (Al) + Al4Ca eutectic had a much finer structure as compared with the Al–Si eutectic, which suggests a possibility of reaching higher mechanical properties as compared to commercial alloys of the A356 type. The influence of the annealing temperature within the range up to 600 °С on the structure and hardness of the Al–Ca–Sc experimental alloys was studied. It was determined that the maximum hardening corresponded to the annealing at 300 °С, which was due to the precipitation of Al3Sc nanoparticles with their further coarsening. With an example of an Al-7.6% Ca-0.3% Sc model experimental alloy, a principal possibility of manufacturing aluminium casting alloys based on the (Al) + Al4Ca eutectic was demonstrated. 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 casting.

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