Optimization of hardening of Al–Zr–Sc cast alloys

The effects of composition, cooling rate after the end of solidification, and annealing regime on the structure and hardening of binary and ternary alloys of the Al–Sc–Zr system are studied. The liquidus in Al–Sc–Zr alloys is experimentally assessed in order to facilitate the correct choice of casting temperatures. The precipitation during slow cooling after the end of solidification causes hardening in the as-cast state and decreases the hardening effect during annealing. It is shown that the full hardening ability of precipitates can be achieved only upon their homogeneous distribution in the matrix. The optimum total concentration of Sc and Zr in aluminium alloys should be about 0.3 wt% at the ratio Zr:Sc ≥ 2. That allows conventional casting temperatures and considerable hardening during annealing.