Dual-scale precipitation hierarchical strengthening in low-solute Cu–Ni–Si–Co alloys driven by vacuum-assisted die casting and deformation

Precipitation strengthening in Cu–Ni–Si alloys is generally attributed to nanoscale continuous precipitate phases (CPPs), while discontinuous precipitate phases (DPPs) are often considered detrimental because of their coarse morphology. However, the role of DPPs in deformed Cu–Ni–Si alloys and their interaction with CPPs and deformation substructures remains insufficiently understood. In this work, a low-solute Cu–2.0Ni–0.6Si–0.8Co (wt.%) alloy was processed by vacuum-assisted die casting (VADC), followed by rolling and direct aging, to promote early-stage DPPs precipitate while retaining a high density of deformation substructures. This processing route results in a microstructure characterized by the coexistence of DPPs and CPPs across multiple length scales. The results indicate that the pinning effect of VADC-induced DPPs arising from high solute supersaturation, together with the precipitation and pinning of nanoscale CPPs, effectively suppresses recrystallization and promotes recovery-dominated softening, thereby maintaining a high dislocation density and enhancing the strengthening efficiency of CPPs. As a result, a favorable combination of hardness (316.5 ± 8.4 HV), ultimate tensile strength (755 ± 19 MPa), electrical conductivity (35.8 ± 0.4% IACS), and plasticity (6.0 ± 0.4% elongation) is achieved through dual-scale precipitation strengthening. This study provides a clearer understanding of the cooperative effects between DPPs, CPPs, and deformation structures, offering useful guidance for microstructural design of high-performance Cu–Ni–Si alloys.