The influence of La addition on the microstructure and properties of 10 Mg

2

Si/Al-Cu-xLa（x=0

0.2

0.4

0.8

mass fraction）composites was investigated.The results indicate that the eutectic Mg

2

Si phase is refined remarkably in the 10 Mg

2

Si/Al-Cu composites with the addition of La

which is changed from a large Chinese character to a thin strip or dot

and the mechanical properties of the composites are improved.significantly The 10 Mg

2

Si/Al-Cu-0.8La composites present 133 HV in hardness

however existence of large needle-like La-rich phases leads to the reduction of its ultimate tensile strength（UTS）and elongation.Therefore

the squeeze casting was applied to improve the microstructure and properties of 10% Mg

2

Si/Al-Cu-0.8La composites.The experiments show that squeeze casting can refine significantly Mg

2

Si and needle-like La-rich phases

leading to the increase of hardness and mechanical properties.The optimal properties can be obtained in 10 Mg

2

Si/Al-Cu-0.8La composites prepared by the squeeze casting（SC）assisted with ultrasonic treatment（UT）

which exhibit 146 HV in hardness

336 MPa in UTS and 2.5%in elongation

respectively

which are increased by 16.8%

22.2% and 92.3%

respectively

compared with those of ones fabricated by gravity casting（GC）.