Improved mechanical strength, ductility, and electrical conductivity of Cu–Ni–Si alloys after multi-pass continuous extrusion and aging processes

Abstract

The manufacture of high strength, high electrical conductivity, and high ductility of Cu–Ni–Si strips in the industry is a challenging problem due to the mutually exclusive relationships among the three properties. However, the results obtained in the present study demonstrated that the trade-offs can be improved by employing a multi-pass continuous extrusion and aging process. The mechanical strength and electrical conductivity increase with the increase of extrusion number before three passes with the help of dynamically occurred recrystallization and precipitation. The yield strength, however, drops after four-pass extrusion, suggesting that a too-high strain deformation during continuous extrusion is not favorable. After aging, alloys that suffer fewer extrusion passes exhibit higher yield strengths, indicating that it is the precipitates rather than the microstructure that dominates the mechanical properties of Cu–Ni–Si alloys. Interestingly, the fracture elongation after aging for alloys experienced more pass number increases, which can be attributed to the refined grain size and reduced dislocation densities. After a two-pass continuous extrusion and aging process, the tensile strength and fracture elongation can reach 629 MPa and 16.5%, respectively, increasing approximately by 28.8% and 13.4% compared with those before aging. It is therefore significant to design an appropriate deformation process (strain) for continuous extrusion to obtain high strength, high conductivity, and high ductility Cu–Ni–Si strips.