Microstructure

tensile strength and hot cracking tendencies of cast Al-7Zn-2.5Mg-Cu alloy with Al-5Ti-B grain refiner contents including 0

0.2%

0.5%

0.8% and 1.2% were investigated. The results show that grains of Al-7Zn-2.5Mg-Cu alloy are refined obviously by adding Al-5Ti-B grain refiner. With increasing in the refiner addition

the grain size is decreased firstly and then slightly increased. The smallest grain size with 66 μm can be observed with 0.8%grain refiner. As grain size decreases

the number of eutectic is increased

resulting in the improvement of tensile strength and decrease of hot cracking tendencies of cast Al-7Zn-2.5Mg-Cu alloy. Tensile strength and grain dimension follow the relationship of σb=47.227 11+1 325.354 77×d-1/2

and hot cracking tendencies and grain dimension follow the relationship of H=41.739 12+0.573 3×d. Eutectic phase also affects the tensile strength and hot cracking tendency of the alloy. Under experimental conditions

tensile strength is decreased and hot cracking tendency is decreased firstly and then raised with increasing in the eutectic number.