Effect of 0.5 wt.% Cr on Precipitation Evolution and Recrystallization Behavior in Cu-Ni-Co-Si-Zn Alloys

Abstract

This study investigates the effects of 0.5 wt.% Cr on precipitates, texture, recrystallization, and properties in Cu-Ni-Co-Si-Zn alloys. During melting, Cr promotes the formation of (Cr, Co)₃Si primary phases, which contribute to the refinement of the initial grains. The addition of Cr significantly increases the activation energy for second-phase precipitation by 46%, thereby retarding the precipitation kinetics by raising the nucleation energy barrier. However, in the early stage of aging, the co-precipitation of BCC-Cr (three variants) and δ-(Ni, Co, Cr)₂Si results in a multi-phase strengthening effect, markedly enhancing the peak hardness. Cr promotes the transformation of δ-(Ni, Co)₂Si into the more stable δ-(Ni, Co, Cr)₂Si phase and induces the precipitation of fully coherent β-(Ni, Co)₃Si, significantly delaying over-aging and enhancing hardness retention. The formation enthalpies of δ-(Ni, Co, Cr)₂Si and β-(Ni, Co)₃Si are lower than those of δ-(Ni, Co)₂Si and β-Ni₃Si, indicating that the Cr-containing precipitates exhibit stronger thermodynamic driving force and higher structural stability after overcoming the precipitation activation energy. The effect of Cr on grain exhibits a pronounced time-dependent behavior: during short-term aging (2 h), Cr suppresses the precipitation of secondary phases, thereby increasing lattice distortion (KAM value increases by 3.4%), promoting the formation of Cube recrystallization texture (1.82), and weakening the Brass texture (from 5.89 to 4.29). After prolonged aging (20 h), the 0.5Cr alloy retains a high precipitate density through suppressed coarsening, strengthening grain boundary pinning. As a result, the Brass texture (1.92) is retained, and the recrystallization fraction (2.0%) remains significantly lower than that of the 0Cr alloy (23.6%), ultimately leading to a mixed microstructure composed of recrystallization textures (Rt-C: 1.70, R: 2.43) and deformation textures inherited from cold rolling.