Phase Composition, Structure, and Hardening of Alloys Containing 6% (Ca + Si) in the System Al–Ca–Si–Zr–Sc

Abstract

Thermo-Calc calculations and experimental methods (optical and electron scanning microscopy, and electron microprobe analysis) were used to study the phase composition of alloys of the Al–Ca–Si–Sc–Zr system with the same scandium and zirconium contents (0.1 and 0.25 wt %, respectively) and the same total silicon and calcium content (6 wt %). It was shown that the hardening due to the precipitation of nanoparticles of the phase Al₃(Zr, Sc)–L1₂ reaches a maximum after annealing at 300–450°C in alloys within the phase region (Al) + Al₄Ca + Al₂Si₂Ca, where (Al) stands for a solid solution based on aluminum. In alloys within this region, almost all of the zirconium and scandium are contained in (Al), and the silicon content of the alloys is minimum. However, Zr and Sc additions have almost no effect on hardening in alloys within the (Al) + (Si) + Al₂Si₂Ca phase region. The aluminum–calcium eutectic has an essentially finer structure than that of aluminum–silicon.