The effects of cooling rate and Nd modification on the microstructure of hypoeutectic Al-11 Mg

2

Si alloy were investigated. The results indicate that the microstructure of hypoeutectic Al-11 Mg

2

Si alloy is composed of primary α-Al and（α-Al+Mg

2

Si） phase. With the increase of the cooling rate of the mould

the eutectic temperature is decreased and the undercooling is increased

where the area fraction of primary α-Al phase is gradually decreased

and the Mg

2

Si eutectic phase is converted from coarse lamellar to fine fibrous. Moreover

the secondary dendrite spacing of Mg

2

Si phase is decreased and the microstructure is refined. After 0.4% Nd modification

with the increase of cooling rate

the addition of modifier leads to the partial melt undercooling of Mg

2

Si eutectic during solidification

improving the nucleation rate. Mg

2

Si is uniformly distributed in form of flocculent in eutectic of Al-11 Mg

2

Si alloy