The effects of different Zr content（0

0.1%

0.15%

0.2%

0.25%）on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy were investigated. The alloy with Zr content of 0.1% and 0.25% was treated by ultrasonic melt treatment before pouring

and the microstructure and mechanical properties after ultrasonic treatment were analyzed. The results reveal that Zr can refine grain size

however

with Zr content increase

composition segregation is deteriorated

and the secondary phase is increased in the grain

resulting in the increase of firstly and then decrease of as-cast tensile strength with decrease of elongation. After ultrasonic melt treatment

the grains are refined with uniform distribution and average size less than 50 μm

meanwhile

the second phase in the crystal disappears completely

and composition segregation is reduced significantly.