The homogenization process and microstructure of 7075 alloy ingot were analyzed by optical microscopy（OM）

scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The results show that the microstructure of Al-Zn-Mg-Cu-Cr alloy ingot consists of Al matrix and Mg（Zn

Al

Cu）2non-equilibrium eutectic phase.With homogenized at 460 ℃

the dendritic structure in the alloy disappears partly

and low melting point phases is dissolved insufficiencily

so alloy constituent exhibits unevenly diffusion

while with homogenized at 470 ℃

part of structure is overburned.After homogenized at 460℃×5h+480℃×24hand 460℃×5h+490℃×24h

the eutectic structure at grain boundary are bascally eliminated

however

grain size is grew up obviously

where the final grain size of the alloy at two homogenizing treatments reaches 120μm and 150μm

respectively.After treated at 400℃×5h+460 ℃×24h+470 ℃×24h

the eutectic structures is totally dissolved

and grain size is about 75μm.It is indicated that the three level homogenization treatment is desirable for treating Al-ZnMg-Cu-Cr alloy.