Effects of Co and Si additions and cryogenic rolling on structure and properties of Cu–Cr alloys

Abstract

Cu–Cr alloys have been widely used in industrial applications owing to their good combination of mechanical properties and electrical conductivity. However, the comprehensive performance of the alloy needs to be further improved to meet the harsh working environment. Hence, in this study, a new type of Cu–Cr alloy with Co and Si additions together with cryogenic rolling (CR) was designed and investigated. Microstructure analysis confirms that the Cr15Co9Si6 and Co2Si phases are formed with Co and Si additions into the Cu–Cr alloy. For the more, partial Cr15Co9Si6 phase decomposes during heat treatment process, and the Co2Si and Cr precipitates are precipitated from matrix during aging process. The improvement of tensile properties of the Cu–1Cr–1Co–0.6Si alloy is mainly attributed to the precipitation strengthening and grain boundary strengthening, and is also benefited from dislocation density strengthening, twin boundary strengthening, and solid solution strengthening. The electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy decreases dramatically mainly due to the increase of impurity scattering caused by surplus Si atoms. CR deformation is helpful for more solute atoms precipitated from the supersaturated solid solution during aging process, and thus the electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy increases with increasing deformation amount. After homogenizing treatment at 900 °C for 2 h, hot rolling by 60% at 900 °C, solution treating at 990 °C for 4 h, cold rolling by 90%, and aging at 440 °C for 1 h, the hardness, yield strength (YS), ultimate tensile strength (UTS), and electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy are 214.6 HV, 663.7 MPa, 745.9 MPa and 41.6%IACS, respectively, which exhibit good mechanical properties with a proper electrical conductivity. These results provide a feasible route for developing high performance Cu–Cr alloys.