With the help of thermal analysis system

the modification effects of RE on eutectic Si in Al-20Si-1.5Cu-0.4Mg alloy were investigated. Thermal analysis curves and microstructure of the eutectic Si with various RE additions were observed at a given P content of 0.08%. The results reveal that when RE addition is lower than 0.6%

with its increase

eutectic Si phase in the alloy is gradually converted from acicular structure into dispersedly short rod with decreasing in grain size

where eutectic growth temperature is decreased and difference of eutectic growth temperature is increased

showing better and better modification effects. However

with RE addition more than 0.6%

modification effects become worse

and eutectic growth temperature is increased with decreasing in difference of eutectic growth temperature. Difference of eutectic growth temperature exhibits desirable corresponding relationship with the modification effect of RE on eutectic Si.