Effect of scandium on phase composition and hardening of Al–Ca–Si system casting aluminum alloys

Abstract

The paper uses calculation (Thermo-Calc) and experimental (optical and electron scanning microscopy, electron microprobe analysis) methods and studies phase composition of the system Al–Ca–Si–Sc in the region of aluminum alloys. It studies the effect of annealing in the range of up to 550 °C on the structure and hardness of alloys containing 0,3 % of Sc. The study demonstrates that maximum hardening due to release of Al3Sc (L12) phase nanoparticles is achieved after annealing at temperatures of 300–350 °C in alloys falling within the phase region (Al) + Al4Ca + Al2Si2Ca ((Al) – solid aluminum-based solution). Scandium enters the (Al) composition in alloys of this region in full, and silicon concentration in such composition is minimal. On the other hand, hardening effect in alloys of the (Al) + (Si) + Al2Si2Ca phase region is near-zero. The study substantiates fundamental possibility of creating (Al) + Al4Ca + Al2Si2Ca eutectic-based cast alloys, which can be hardened without quenching.