Effects of Si and Co co-addition on the comprehensive properties and microstructure of Cu-Cr-Zr alloy

In this work, the effects of Si and Co additions on the mechanical properties, electrical conductivity, corrosion resistance and microstructure of Cu-Cr-Zr alloy were studied. The peak-aged Cu-Cr-Zr-Si-Co alloy exhibits an ultimate tensile strength of 686.73 MPa, a hardness of 233.14 HV, and an electrical conductivity of 71.72%IACS. Compared with the peak-aged Cu-Cr-Zr alloy, the ultimate tensile strength and hardness increase by 20.1% and 13.2% respectively, while the electrical conductivity only decreases by 5.3%. The corrosion resistance of Cu-Cr-Zr alloy can be effectively enhanced by the combined addition of Si and Co, as evidenced by a 37.9% decrease in corrosion current and a 30.7% increase in polarization resistance. In 3.5 wt.% NaCl solution, both alloys develop corrosion films with a double-layer structure. The charge transfer resistance of the inner layer is much higher than that of the outer layer, which is the key factor dominating the corrosion resistance. Compared with the Cu-Cr-Zr alloy, the Cu-Cr-Zr-Si-Co alloy contains more numerous and finer Cr-rich precipitates, along with the formation of Cu4Zr precipitates. Moreover, the Cu-Cr-Zr-Si-Co alloy exhibits a larger grain boundary length per unit area and a higher proportion of Σ3 grain boundary. The enhanced mechanical properties of the Cu-Cr-Zr-Si-Co alloy are attributed to the synergistic effects of grain boundary strengthening, Orowan strengthening, and modulus strengthening.