Patent ID: 7100669

Claim:
A method of casting a hypereutectic aluminum silicon alloy, comprising the steps of preparing a molten hypereutectic aluminum silicon alloy consisting essentially of: 16–28% by weight silicon, 0.90–4.9% by weight copper, 0.3–1.3% by weight magnesium, 0.005–0.1% by weight phosphorus, less than 0.3% by weight manganese, less than 0.2% by weight titanium and less than 0.1% by weight zinc; pouring said molten hypereutectic aluminum-silicon into a flask at a temperature at or greater than 1600° F., said flask containing a foam pattern having a configuration of an item to be cast; applying external pressure in the range of 5.5 to 50 ATM to the molten hypereutectic aluminum-silicon in the flask before the foam pattern is entirely ablated by the molten alloy; and maintaining the pressure on the molten hypereutectic aluminum-silicon through solidification to produce a cast article having a reduced average silicon particle size by 15 to 25%, compared to the average silicon particle size realized without applying and maintaining said external pressure.