Under constrained condition, severe plastic deformation at high speed can be carried out at extreme low temperature without annealing. Homogeneously Ultrafine-Grained (UFG) 7075 aluminum alloy (e.g. Al-Zn-Mg alloy) with size about 200 nm was fabricated. Evolution of microstructure was studied by transmission electron microcopy (TEM). Different deformations were observed. Factors such as low temperature and dynamic recrystallization contributing to microstructural evolution were discussed.