Effects of yttrium on microstructure and mechanical properties of Mg-3Zn-xY（x=0.5

1.5

3

6）alloys were investigated by X-ray and microscope.The results show that the size and amounts of particles in the matrix and at grain boundary are increased with increasing yttrium content.The type of second phase in the alloy is found to be dependent upon the Zn/Y ratio.With the Y content increases

the second phase is converted from Mg

7

Zn

3

+I phase to I phase +W phase

and to W phase +H phase to H phase.The shapes of the second phases at the grain boundaries are transformed from punctate to short rodlike

and to reticular particles.The tensile strength

hardness and impacting toughness of alloy are improved while the plasticity is decreased with Y content increasing.However

the comprehensive mechanical properties are descended with 6% Y addition.