Effect of Cr addition on the microstructure evolution, precipitation behavior and properties of Cu–Ag alloy

This investigation systematically explores the impact of minor Cr additions on the microstructural evolution, precipitation kinetics, mechanical properties, and electrical properties of Cu–Ag alloys, with a specific focus on Cu–6%Ag-(0.4%Cr). The alloys underwent casting through a vacuum induction furnace, followed by meticulous treatments involving solution heat and aging at varied temperatures and durations. Results indicate a significant improvement in the mechanical properties of Cu–Ag alloy upon Cr addition, with only a slight reduction in electrical conductivity. As per differential scanning calorimetry (DSC) measurements, the activation energy for continuous precipitation in the Cu–Ag–Cr ternary alloy is slightly higher than that in Cu–Ag. However, Cu–Ag–Cr lacks peaks corresponding to the discontinuous phase. Microstructural analysis unveils that Cr incorporation suppresses the discontinuous precipitation of Ag, fostering continuous precipitation during aging. Moreover, both micro-sized and nano-sized Cr particles were detected in the Cu–Ag–Cr alloy, contributing to the formation of finely spaced continuous Ag precipitates and fine Cr precipitates. This intricate microstructure imparts higher hardness and strength to the alloy compared to Cu–Ag. Specifically, following aging treatment at 450 °C for 2 h, the Cu–6%Ag-0.4%Cr alloy exhibited a remarkable increase of 76.1 % in hardness, 43.6 % in strength, and a moderate decrease of 15.8 % in conductivity.