Hot tearing susceptibility(H

TS

)and microstructure evolution of die casting Mg-10Zn-yAl（y=0

2

3.5

5）alloys（ZA series alloys）were investigated.The H

TS

of alloys was investigated using rod die casting mold and it was determined based on the location and quantity of cracks in the rods.The H

TS

results show that Al is effective to improve the hot tearing resistance of ZA series alloys.The H

TS

of ZA105 alloy reaches the lowest value.Thermodynamic calculation software（Pandat8.0）was used to calculate solidification paths of ZA series alloys.The results reveal that the correlation between H

TS

and Flep（liquid fraction at the end of primary solidification）is negative

while it between H

TS

and F

TR

（freezing temperature range）is positive.Microstructure analysis by EDS and XRD confirms that Al addition can refine effectively the grain size in the Mg-10Zn alloy.With increasing in Al addition

the amounts of secondary phase are increased

where the secondary phase is mainly Mg

5

Zn

2

in the ascast Mg-10Zn alloy and it is mainly quasicrystal phase(Mg

62～69

Zn

22～25

Al

6～16

)in the other alloys.