Precipitation and dissolution of Ag in ageing hypoeutectic alloys

• Activation energies of precipitation and dissolution of Ag were determined.
• Electrical resistivity test showed less solubility of Ag in Cu at 405 °C.
• Microhardness results indicated more strengthening effect at about 475 °C.
• TEM observations confirmed the precipitation and dissolution of Ag.

Understanding the precipitate kinetics of Ag in proeutectic Cu is valuable to optimize the precipitation and morphology of Ag for high strength high conductivity hypoeutectic Cu–Ag alloys. The precipitation behaviors of as-solution treated Cu28 wt.%Ag alloys were analyzed by differential scanning calorimetric (DSC). The results indicated that the activation energies of Ag-rich phase formation and dissolution were 55.3 ± 22.4 kJ/mol and 129.1 ± 20.7 kJ/mol, respectively. The as-solution alloy was further aged at different temperatures for 2 h. Their microhardness and electrical resistivity were measured. The results demonstrated that at the ageing temperature of 405 °C, less scattering effects reflected more Ag precipitations from Cu matrix than the rest of temperatures. At 475 °C, however, Ag precipitates produced more strengthening effects. Above results were related to the competition between precipitation and dissolution of Ag in proeutectic Cu. This interpretation is supported by TEM observations on Ag precipitation.