Investigation on microstructure development and mechanical properties of large-load and low-speed friction stir welded Cu-30Zn brass joint

In this work, 2 mm thick Cu-30Zn brass plates were successfully joined by using large-load and low-speed friction stir welding. Heat-affected zone was eliminated due to the significantly improved thermal cycle. The stir zone exhibited ultra-fine grains, with high fraction of twin boundaries and low dislocation density. Also, several nanoscale twin boundaries were introduced into the stir zone. Grain structure refinement in the weld was attributed to the combination of discontinuous, continuous, geometric and shear-band-assisted dynamic recrystallization mechanisms. Consequently, the stir zone showed excellent strength-ductility synergy compared to that of the severe plastic deformed and the conventional friction stir welded Cu-30Zn brass. A feasible one-step strategy was developed herein, to increase the strength of the friction stir welded Cu-30Zn brass joint, while avoiding ductility loss. Moreover, this study offers a new insight and choice for joining metals or alloys with higher melting points, such as steel and titanium alloys.