Revealing the role of Cr addition on the microstructure, properties and softening resistance of a pre-aged Cu-Ni-Co-Si alloy

Cu-Ni-Co-Si alloys that undergo pre-aged treatment demonstrate enhanced mechanical and electrical properties, yet exhibit relatively low softening resistance (SR). Herein, 0.1 wt% Cr was doped into the Cu-1.2Ni-0.9Co-0.5Si alloy, and the effects of Cr addition on the microstructure, properties, and softening resistance were systematically investigated. The results indicate that the tensile strength slightly increases whereas the electrical conductivity remains comparable upon Cr addition under the peak-aged condition. Meanwhile, the strength decline during the over-aging stage is significantly mitigated by Cr addition, corresponding to an increase in the softening temperature from 530 degrees C to 580 degrees C. Atom probe tomography (APT) results reveal that Cr increasingly segregates at the interface between the (Ni, Co, Cr)2Si precipitates and Cu matrix as aging progresses, which contributes to the reduced growth/coarsening rate of the (Ni, Co, Cr)2Si precipitates in Cr-doped alloys. Consequently, the enhanced SR with Cr addition can be attributed to the inhibition of growth/coarsening of (Ni, Co, Cr)2Si precipitates and the resultant impediment of dislocation recovery and recrystallization during longterm aging. Additionally, the electrical conductivity of Cr-doped alloys is relatively lower than that of Cr-free alloys during the over-aging stage, which is primarily attributed to the incomplete purification of the matrix and insufficient recrystallization in the Cr-doped alloy.