Effects of Zr on microstructural evolution and mechanical property of Cu-15Ni-8Sn alloy

The Cu-15Ni-8Sn-XZr (wt.%, X=0-0.7) alloys were prepared by vacuum melting, and their microstructural evolutions during the solidification and heat-treatment processes were systematically investigated as well as the corresponding mechanical properties. Zr addition could offer a significant effect on the dendritic morphology by controlling the constitutional supercooling in solidification front, and it also made the gamma-phase more likely to form in the needlelike-shape rather than the lamellar-like shape in subsequent cooling process. After solution treatment, the Zr atoms with a low content of 0.1 wt% were completely solidly dissolved in the alpha-matrix. With its content increasing to 0.3 and 0.5 wt%, the existence form was changed into the nano-scale precipitation phase (Ni5Zr) and then to micron-scale segregation phase (Ni4SnZr). The presence of Zr could significantly extend the aging window of alloy and improve its mechanical properties by inhibiting the nucleation and growth of discontinuous precipitation (DP), and there was few DP even after 16 h aging. The optimal combination of properties was obtained for Cu-15Ni-8Sn-0.5Zr alloy aged at 673 K for 4-16 h, including a hardness of 330HB, ultimate tensile strength (UTS) of 980 MPa and electrical conductivity of 9%IACS.