Ultra fine grain of Cu-Zn alloy evolved by multi directional forging and its thermal and mechanical properties

A Cu-30 mass%Zn alloy was multi directionally forged (MDFed) at 300 K and 77 K. Dislocation walls, subboundaries and grain boundaries were gradually developed with increasing strain to form ultra fine grains (UFGs). Furthermore, the evolution of UFGs was drastically stimulated by mechanical twinning. Therefore, it was revealed that the grain refinement in a Cu-Zn alloy during MDF was induced by both mechanisms of mechanical twinning and continuous dynamic recrystallizatrion. When MDFed to a cumulative strain of Sigma Delta epsilon = 6, the grain size obtained was 18 run at 77 K and 22 nm at 300 K. The MDFed alloy exhibited almost constant ductility irrespective of cumulative strain and MDF temperature, while the tensile strength increased monotonically with increasing cumulative strain. Thermal stability of the UFGed Cu-Zn alloy decreased with increasing cumulative strain and decreasing MDF temperature.