The effects of complex modification of Sb+Ce on the primary Mg

2

Si phase in 20%Mg

2

Si/Al-5Si composites fabricated by in situ reaction were investigated.The results reveal that the average size of the primary Mg

2

Si particles is decreased firstly and then increased with the 0.2%Sb+xCe modification.The primary Mg

2

Si particles reach 28μm with uniform distribution with the addition of 0.2%Sb+0.6%Ce.With the addition of 0.4%Sb+xCe

the primary Mg

2

Si particles can be modified effectively and its average size reaches 30

4

0μm.The optimum modification effect can be observed with the addition of 0.6%Sb+xCe

where average size of primary Mg

2

Si particles reaches 27

3

1μm with the higher roundness and more uniform distribution.