Microstructure and mechanical properties of a high strength Cu-Ni-Si alloy treated by combined aging processes

High strength Cu-Ni-Si alloys were potential elastic conductive materials due to their high strength and high electrical conductivity. To address the trade-off between strength and electrical conductivity, a combined aging process has been developed to enhance the properties of a Cu-6.0Ni-1.0Si-0.5Al−0.15Mg-0.1Cr alloy after an initial thermo-mechanical heat treatment. The microstructure evolutions of the studied alloys were investigated by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The mechanical and physical properties were evaluated through hardness measurements, tensile test and conductivity test. The results demonstrated that a hardness value of 381 HV, an ultimate strength of 1155.8 MPa, an elongation of 3.5%, and an electrical conductivity of 25.2%IACS were achieved after an appropriate combined aging process. Cold rolling led to the formation of a dense dislocation wall as a result of dynamic interactions among the dislocations and precipitates. During the second stage of aging, nanoscale precipitates formed in the first stage slowly coarsened and effectively pinned dislocations motion. The combined aging process increased the hardness and strength, without sacrificed the electrical conductivity. This work provided an effective route for balancing the strength and electrical conductivity of copper alloys.