The effect of hydraulic pressure applied during solidification on the mechanical properties of hypereutectic Al-Si alloys (15-21wt%Si) was studied. The results obtained are as follows:
(1) The eutectic structure of unmodified hypereutectic Al-Si alloys were refined by the pressure applied during solidification.
(2) The mechanical properties were improved with an increase of the applied pressure, and an appreciable improvement was attained at above 20kg/mm².
(3) An ingot almost free from the casting defects was obtained by applying a pressure above 20kg/mm².
(4) The mechanical properties of the ingot solidified under the hydraulic pressure were not lower than those case with the treatment of modification.
(5) Dimple markings were observed on both the tensile and impact fractured surfaces.