The as-cast and homogenized microstructure of DC 7050 aluminum alloy were investigated by differential scanning calorimeter （DSC）

optical microscope （OM）

scanning electron microscope （SEM） and X-ray diffraction （XRD）. The results reveal that there exists an amount of non-equilibrium Mg（AlZnCu）2 phase with η-MgZn2 crystal structure in DC 7050 aluminum alloy ingots. The non-equilibrium phase is fully dissolved into the alloy matrix at 477℃ to further transform into large spherical Al2CuMg （S phase） at 490℃. With homogenization treatment at 460℃

the non-equilibrium Mg（AlZnCu）2 phase with η-MgZn2 crystal structure totally disappeares in the alloy with occurrence of spherical S phase in both intercrystal and grain. During cooling process

η-MgZn2 phase and S phase are precipitated from the grain subsequently

however

S phase disappears in the grain of the 7050 alloy ingots at 260℃.