Effects Of Pre-annealing Process On Microstructure And Properties Of The Cu-Ag Microcomposites

Cu-6%Ag, Cu-12%Ag and Cu-24%Ag (mass fraction) alloys were prepared by vacuum melting and pre-annealed with different processes. The microstructure and mechanical properties of Cu-Ag alloys during aging treatment were investigated. The effect of aging treatment on the microstructure and mechanical properties of Cu-6%Ag alloys was discussed. Cu-6%Ag filamentary microcomposites were prepared by heavy cold drawing combined with solid solution and aging treatment with different processes. The effect of aging treatment was investigated by observing the microstructure and determining the mechanical and electrical properties during cold drawing.During aging treatment, discontinuous precipitation reaction can occur along high-angle grain boundaries and continuous precipitation reaction within Cu dendritic arms. Abundant high-angle grain boundaries result in a precipitation reaction that is predominantly discontinuous in Cu-6%Ag. Net-like eutectic colonies surrounding Cu dendritic arms result in a precipitation reaction that is predominantly continuous in Cu-24%Ag. In Cu-12%Ag, continuous precipitates within Cu dendritic coexist with discontinuous precipitates next to high-angle grain boundaries. Aging only for 1 h can significantly increase the hardness although the precipitation reaction is insufficient. The increasing rate of the hardness becomes slow as aging time longer than 1 h. The hardness keeps approximately constant for Cu-12%Ag and Cu-24%Ag and slightly decreases for Cu-6%Ag with increasing aging time from 16 to 37 h. The precipitation reaction during aging treatment has more significant hardening benefit to the alloys with lower Ag contents.The microstructure of Cu-6%Ag contains single Cu-rich matrix after solid treating at 730 ℃ for 8 h and then 760 ℃ for 4 h and 780 ℃ for 4 h. The microstructure contains Cu-rich matrix and Ag precipitates after aging treatment. The hardness of Cu-6%Ag alloy increases in the early aging period and then decreases. The temperature of aging treatment influences the annealing time when peak hardness value is obtained. During aging treatment, the precipitation reaction has a more significant hardening benefit to Cu-6%Ag compared with solution strengthening. The electrical conductivity of Cu-6%Ag increases with the increasing of aging time. The starting time and increasing velocity of the electrical conductivity are dependent on the temperature of aging treatment.For Cu-6%Ag, aging treatment can improve the ultimate tensile strength level during cold drawing and the electrical conductivity simultaneously by increasing the aging temperature or time. After aging at 450 ℃ for 32 h, the preferable combination property is acquired at η = 7.0. The tensile strength achieves 1320 MPa and the electrical conductivity is retained at 67.6% IACS. After aging at 450 ℃ for 2 h, the tensile strength reaches to 1310 MPa and the electrical conductivity is still maintained at 68.3% IACS at the same deformation level.