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

Abstract

The phase composition of the Al–Ca–Si–Sc system is investigated in aluminum corner uisng computational (Thermo-Calc) and experimental (optical microscopy, scanning electron microscopy, and electron probe microanalysis) methods. The influence of annealing on the structure and hardness of alloys containing 0.3 wt % Sc is investigated in the region up to 550°C. It is shown that the maximum in the hardening curve caused by the isolation of nanoparticles of the Al3Sc (L12) is attained after annealing at temperatures of 300–350°C in alloys belonging to the phase region (Al) + Al4Ca + Al2Si2Ca ((Al) is the aluminum-based solid solution). Scandium completely enters the (Al) composition in alloys of this region, while the silicon concentration is minimal in it. On the other hand, hardening is almost absent in alloys from the (Al) + (Si) + Al2Si2Ca phase region. The possibility in principle to form the casting alloys based on the (Al) + Al4Ca + Al2Si2Ca eutectic hardened without quenching is substantiated.