• Multi-stage thermomechanical treatment significantly enhances the ultimate tensile strength of directionally solidified Cu−15Ni−8Sn alloy, achieving 1509 MPa after aging at 400 °C for 0.25 h, which is over 200 MPa higher than single-stage treatment.
• Grain refinement and intensified 〈111〉 fiber texture are identified as key microstructural factors contributing to the improved mechanical properties.
• Directional solidification combined with multi-stage thermomechanical treatment enables the fabrication of Cu−15Ni−8Sn alloy wires with a nano-layered structure, overcoming traditional casting segregation issues.
• The study provides a promising alternative to beryllium−copper alloy for high-performance electrical connectors, with superior stress relaxation resistance and stable conductivity at high temperatures.