Phase transformation behaviors and properties of a high strength Cu-Ni-Si alloy

High strength and high electrically conductivity Cu-Ni-Si alloys are important candidate materials for extending the life of currently used elastic-conductor materials. Phase transformation behaviors and properties of a synthesized Cu-6.0Ni-1.0Si-0.5Al-0.15Mg-0.1Cr alloy were investigated systematically. After homogenized for 4 h at 940 °C, hot rolled by 80% at 850 °C, solution treated for 6 h at 970 °C, cold rolled by 50%, and annealed for 60 min at 450 °C, the studied alloy approached physical properties of 1097.5 MPa in tensile strength and 26.4%IACS in electrical conductivity. Transmission electron microscope observations showed that four precipitation phases including δ-Ni₂Si, β-Ni₃Si, β-NiAl, and γ′-Ni₃Al were formed in the studied alloy, which was subjected to different annealing temperatures. A detailed diagram for isothermal decompositions has been established. The high strength of the studied alloy was primarily attributed to the Orowan precipitation strengthening, and secondary attributed to the solid solution strengthening, the Hall-Petch type grain boundary strengthening, and the work hardening. Multi-precipitation phases of Ni₂Si, γ′-Ni₃Al, β-Ni₃Si played significantly into the strengthening effects, and the low electron diffraction influence of Mg and Cr contributed to both solution strengthening and maintaining a high electrical conductivity. Multi-phase precipitation strengthening and using trace amount alloying elements for solution strengthening will be a new strategy to develop high strength and high electrical conductivity copper alloys.