The effects of super-gravity field on the eutectic microstructure and microhardness of Al-12 Si alloy without modification and with sodium modification were investigated by centrifuge.The results reveal that

the central eutectic silicon in the un-modified Al-12 Si alloy can be refined significantly and granulated in the super-gravity field

and most of the central eutectic silicon presents granular with a diameter of about 0.7μm with solidified at 4 000 g（g=9.8 m/s

2

）.In addition

the central eutectic silicon can be refined and granulated to a higher degree under compound action of super-gravity field and sodium salt metamorphism

and the central eutectic silicon is basically granular with a diameter of about 0.3μm when the super-gravity field reaches 3 000 g.With the increase of gravity field

the central hardness（HV）of the un-modified alloy is increased gradually and reaches the maximum value of 72 at 4 000 g.The central hardness（HV）is increased more obviously when the sodium salt metamorphic alloy is solidified in the super-gravity field and reaches the maximum value of 88 at 3 000 g.