Improving the stability of microstructure and mechanical property in Cu-9Ni-6Sn-0.2Nb alloy by annealing treatment

Cu-9Ni-6Sn-0.2Nb alloys were prepared by a series of preparation-process including hot rolling, solution treatment, cold rolling, annealing treatment, and aging treatment. As the results indicate, the annealing treatment provided a significant role on improving aging stability of the alloys, it obviously decreased volume fraction of DP nuclear sites as well as hinder the growth of DP colony by decreasing the degree of GND and increasing the volume fraction of Sigma 3(n) grain boundaries. Besides, annealing treatment makes Cu-9Ni-6Sn-0.2Nb alloy extend aging window, and the yield strength and Vickers hardness could nearly drop a bit after peak aging compare to the cold-rolled one. Strengthening mechanism has been quantitatively established, indicating that the respective contribution of precipitation strengthening (dominated by gamma ' phases) plays a dominant role in the strength enhancement of the annealed alloy.