Precipitation and dissolution of Ag in ageing hypoeutectic alloys

Abstract

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 Cu28wt.%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±22.4kJ/mol and 129.1±20.7kJ/mol, respectively. The as-solution alloy was further aged at different temperatures for 2h. 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.