The eutectic and primary silicon in hypereutectic Al-Si alloy can be refined by special modification. Then

the nodular silicon hypereutectic Al-Si alloy can be obtained through T6 treatment due to the crystallography flaky-nodular silicon transition. The average aspect ratio of nodular silicon is about 1. 6. In this alloy 99% of the silicon particles have their diameters less than 30 um

and less than 1 % of them have their diameters ranged from 30

4

0um. The nodular silicon Al-22Si is characterized with better plasticity and with an ultimate tensile strength at room timperature up to 300 MPa and a tensile strength at 573K up to 100MPa

being better than those in commercial Al-22Si piston alloy. By way of contrast with commercial hypereutectic of Al-Si alloy the machinability Al-Si alloy tested was improved greatly.