In this paper the modification of Al-Zn alloys with 0.2 ÷ 0.6% concentration at different temperatures by RE were investigated. The results showed that, after modification, the grain size of this alloy was reduced in the casting. When the heat treatment, the particle size of the modified alloys increased slower than non-modification. With 04.% RE, the particle size was smallest. RE elements distributed at the border and inside the α particles. The hardness of modified alloys was not only increased, but also decreased after the heat treatment. The hardness values was lowest when RE’s content is 0.4%.
