In-situ 5TiB

2

/Al-7Si composites were fabricated by mixed salt reaction in Al-7Si melt.The effects of TiB

2

and Mg contents on the impact properties of TiB

2

/Al-7Si composites were investigated.As the addition of TiB

2

and Mg element

theα-Al and eutectic Si phases in the composites can be refined

however its impact properties can be weakened.The Al-7Si alloy exhibits the satisfied impact toughness among these composites

and it is about of 14.2J/cm

2

.With the addition of 5%TiB

2

the impact toughness of the composites is further reduced to 12.6J/cm

2

.When the 1.5%or 3%Mg element were added into the 5TiB

2

/Al-7Si composites

the impact toughness of the composites is reduced to 10.9and 10.4J/cm

2

respectively.The fracture morphology of 5TiB

2

/Al-7Si composites is mainly characterized by dimple and quasi-cleavage of a mixed fracture.