Abstract
Fractography was made on impact tested specimens of the Al-Si alloys (4-20%Si) solidified under the hydrostatic pressure up to 30kgf/mm2. A lateral contraction phenomenon was found just under the notch in the hypoeutectic alloys. The alloys containing low or high quantities of Si showed rough fractures. The alloys near the eutectic composition showed flat fractures. All the alloys solidified under 1 atm showed cleavage fractures. The Al-20%Si alloy showed a cleavage fracture independent of the applied pressure. The dimples were observed both on the fractures of the hypo and hypereutectic alloys solidified under the pressure above 10 and 20kgf/mm2 respectively. Inclusions were recognized at the bottom of all the dimples.
