Enhanced strength and thermal stability of Cu–Ni–Co–Si alloys via Mg-modified coherent nanoprecipitates

This study systematically investigates the evolution of hardness, electrical conductivity, and microstructure during aging in Cu-1.35Ni-1.35Co-0.65Si (-0.1Mg) alloys. Aging analysis shows that peak-aged conditions are achieved at 450 °C for 60 min in the Cu-1.35Ni-1.35Co-0.65Si alloy and at 450 °C for 240 min in the Cu-1.35Ni-1.35Co-0.65Si-0.1Mg alloy. The addition of 0.1 wt% Mg significantly enhances the tensile strength from 816.8 MPa to 949.8 MPa while maintaining relatively high electrical conductivity. Transmission electron microscopy (TEM) reveals that the dominant precipitates in the Cu-1.35Ni-1.35Co-0.65Si and Cu-1.35Ni-1.35Co-0.65Si-0.1Mg alloys are (Ni,Co) 2 Si and δ-(Ni,Co) 2 Si, respectively. In particular, the δ-(Ni,Co) 2 Si phase exhibits a high degree of coherency with the Cu matrix. Strength-contribution analysis indicates that precipitation strengthening is the dominant strengthening mechanism in both alloys, and that Mg addition further enhances this contribution.