Effect of Si addition on the microstructure and mechanical properties of a Cu-Cr-Ag alloy with high strength and electrical conductivity

Abstract

The high-temperature mechanical properties of Cu-Cr alloys were limited, while adding alloying elements could inhibit the coarsening of Cr precipitates and improve the high-temperature mechanical properties. The Cu-Cr-Ag and Cu-Cr-Ag-Si alloys were designed and fabricated, and their microstructure and mechanical properties were investigated to achieve high-strength and high-electrical-conductivity copper alloys. The Cu-Cr-Ag alloy treated by two-step cold rolling and aging treatment achieved an ultimate tensile strength of 620 MPa, yield strength of 600 MPa, electrical conductivity of 85.6 % IACS, and elongation of 15.7 %. Adding Si increased the high-temperature strength, room-temperature elongation, and low-temperature elongation of the Cu-Cr-Ag alloy, while decreasing the electrical conductivity, room-temperature strength, and high-temperature elongation. Nanoscale Cr particles were detected in the Cu-Cr-Ag alloy, while nanoscale Cr and Cr₃Si particles co-existed in the Cu-Cr-Ag-Si alloy, among which Cr particles were the main strengthening precipitates. The curves of precipitation kinetics indicated that adding Si promoted the precipitation in the Cu-Cr-Ag alloy. Low-, room-, and high-temperature mechanical properties measurements showed that the strength variation depended on the average size of the main precipitates. The decrease in the high-temperature strength was attributed to the coarsening of the Cr precipitates. At low temperature, the average size of the precipitates was essentially the same as that at room temperature, thus the low-temperature strength was comparable to the room-temperature strength. These findings indicated that Cu-Cr-Ag and Cu-Cr-Ag-Si alloys would exhibit superior electrical and mechanical properties.