The influence of cooling rate and RE content on microstructure and hardness of Al-Sc alloy was investigated by the combination of vacuum induction melting and spray casting. The results indicate that the equiaxed crystal structure in as-cast alloy is gradually refined with the increase of Sc content

and desirable refinement effect can be obtained in Al-0.8 Sc hypereutectic alloy with the average grain size of 106 μm

which is reduced by 97.6% in comparison with that of pure Al. Due to the strong chilling effect of copper mould injection

non-equilibrium solidification microstructure of the fast-cooling Al-Sc alloy is characterized by preferentially grown columnar crystals

which is typically transformed to equiaxed grain after Sc addition

and the ratio of latter is enlarged as the Sc content increases. The increase of cooling rate inhibits the formation of primary Al

3

Sc phase

which is favorable to supersaturated solid solution. However

the weakening of precipitation strengthening effect results in a lower microhardness of the fast-cooling alloy than that of the as-cast alloy.