Microstructure regulation and strengthening behavior of Cu–15Ni–8Sn alloy microalloyed with multi-elements

This study systematically investigated the microstructural evolution and strengthening mechanisms of Cu-15Ni-8Sn-X alloys through multi-element microalloying (Si, Ti, P) and process optimization. The alloys were prepared using vacuum medium-frequency induction melting, followed by hot extrusion and cold working processes. Microstructure characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC), were employed to elucidate the synergistic effects of microalloying elements on dendritic refinement, segregation suppression, and precipitation behavior. The results indicated that the addition of 0.3% Si, 0.3% Ti, and 0.1% P significantly refined the as-cast dendritic structure and suppressed macrosegregation of Sn elements. The optimized homogenization treatment maintained at 860°C for 9 h effectively alleviated the dendritic segregation and promoted the dissolution of Sn-rich phases. After hot extrusion and solution treatment, undissolved second phases (such as Ni 2 Si and Ni 3 Ti) pinned the grain boundaries, refining the grain size to below 10 μm and significantly inhibiting the growth of recrystallized grains. During aging, the single-layer lamellar unit spacing of discontinuous precipitation (DP) phases increased from 78 nm to 108 nm, which retarded the growth rate of discontinuous precipitates and extended the peak aging time from 2 h to 6 h. The peak-aged alloy exhibited an ultimate tensile strength of 1299 MPa, a yield strength of 1243 MPa, an elongation of 5%, and a Vickers hardness of 402.9 HV. The analysis of strengthening mechanisms revealed that the strength of the alloy was mainly contributed by precipitation strengthening (474.3 MPa), dislocation strengthening (382 MPa), and grain boundary strengthening (39.3 MPa). This study provides a theoretical basis for the design and engineering applications of high-performance Cu-15Ni-8Sn-based alloys.