A bulk Cu-Zn alloy was multi-directionally forged at 77 K and 300 K to a cumulative strain of ΣΔε=6.0. With increasing strain, the initial grains subdivided gradually to ultrafine grains. Mechanical twins enhanced the grain fragmentation. The formed twins were further subdivided by the other variants of twins. The grain size obtained at ΣΔε=6.0 was about 17 nm at 77 K and 26 nm at 300 K.
