Effect of heat treatment on microstructure evolution, phase transformation and mechanical properties of dual phase Cu-Zn alloy

Effects of heat treatment conditions on the microstructure evolution, phase transformation and mechanical properties of dual phase Cu-Zn alloy were systematically investigated. Meanwhile, the relationship between the nano-hardness and the macroscopic hardness was also discussed in the study. The results show that the β phase rich in Zn, has the phase transformation temperature from 456.5 °C to 827.1 °C. With the increasing of heat treatment temperature, significant (200) (220) α phase to (200) (211) β phase transformation occur and the β phase fraction increases from as-received 13.1–41.3%. The grain becomes coarser and grows rapidly from 32.6 µm to 49.7 µm from temperature 550 °C to 800 °C, the increase of β phase results in the strength increases and the fracture elongation decreases. The β phase fraction has not varied significantly at temperature 750 °C and 800 °C, the strength has a further increase which is mainly attributed to a part of fine needles of Widmanstätten phase begin to form. At the same displacement, the β phase exhibits a much larger load than that of the α phase, the material pile-ups around indent edges of the α phase becomes more evident indicating that the α phase is softer and has a better ductile. The big difference in the predicted hardness and the macroscopic hardness when heat treatment at 750 °C and 800 °C is mainly attributed to the formation of the fine needles of Widmanstätten phase.