Investigation Of Aging Process On Micro Structure And Properties Of High Strength And High Conductivity On Micro-Boron Copper Alloys

Copper and copper alloys are widely used in the electric and electronic, machinery manufacturing, transportation and other industries because of the excellent electrical and thermal conductivities, ease of fabrication as well as good strength and ductility. With the rapid development of these industries, it is necessary to enhance the qualities of high conductivity and high strength cooper alloy. However the electric and strength properties is often difficult to improve simultaneously, and how to enhance the electric and strength properties at the same time to be a hot topic for the researchers.Some new-types alloy such as Cu-B-Zr、Cu-B-Zr-Te alloy have been designed and prepared through alloying principle, the aging behavior, aging dynamics, recovery and recrystallization behaviors were studied, and the results shows that Cu-0.065B-0.5Zr alloy under optimum thermo-mechanical processing can be obtained a combination properties:the tensile strength of532.1MPa, elongation of13.83%, electrical conductivity of79.15%IACS, microhardness of125HV. Increase the content of Zr can obviously improve the mechanical properties, Cu-0.13B-1.0Zr alloy can be obtained a strength of603MPa, microhardness of181.3HV, elongation of14.4%, but the electrical conductivity only under70%IACS.The aging kinetics of Cu-B-Zr alloys were studied through testing the electrical conductivity, the results show that the aging kinetics is consistent with Avrami equation. The age hardelling index n first increases then reduce with the temperature rise, which reach a maximum for Cu-0.065B-0.5Zr and Cu-0.13B-1.0Zr alloy at360,390℃respectively. Larger cold deformation enormously promoted the precipitation of the second phase, which caused the Time Temperature Transformation curve (TTT) showed as a vertical moulding at the beginning stage of aging, and shows a "C" at the end of aging.At the basement of the study about aging kinetic behavior of Cu-B-Zr alloys, the influence of secondary deformation and two steps thermomechanical aging treatment on the mechanical and electrical properties, the results show that the mechanical and electrical properties can be improved simultaneously after two steps thermomechanical aging treatment for Cu-0.065B-0.5Zr alloy. Tensile strength of575.41MPa, electrical conductivity of79.37%IACS were obtained after two steps thermomechanical aging treatment with aging at470℃for2h+20%cold rolling+aging at360℃for2h, the strength has been improved8.2%compared with one step thermomechanical aging treatment. For Cu-0.13B-1.0Zr alloy, secondary deformation can obviously improve the mechanical properties. Tensile strength of684MPa, electrical conductivity of62.5%IACS were obtained with aging at390℃for2h+40%cold rolling, in which the strength has been improved13.4%.A new-type Cu-0.015B-0.14Zr-0.25Te has a very good electric conduction after aging treatment; and the tensile strength is very sensitive to aging temperature, it performs strengthened at330-360℃and softened at other aging temperature. The change of microhardness is inconsistent with tensile strength causing by the large strain inhomogeneous deformation. The deformation near the outside of the specimen along longitudinal section is more severity than inside part, promoted the accruement of recrystallization, and caused the microhardness performing soften. Stable fibrous structure is helped to enhance the strength property at low-and-medium temperature, and at high temperature recrystallization was occurred quickly at the location with dense fiber, which occurred by the merger and migration of grain boundary, it can be considered as a kind of discontinue recrystallization. Tensile strength of507MPa, electrical conductivity of87.3%IACS were obtained with aging at330℃for2h+20%cold rolling.The precipitation behavior of Cu-B-Zr alloys was invested with TEM, the results show that the progress of precipitation contains two patterns, continuous precipitation inner grains and discontinuous precipitation which nearby the subboundary structure, and the continuous precipitation plays a major role throughout this progress. The layer structure produced by discontinuous precipitation gradually coarsens into ball, and the volume fraction of spherical precipitates produced by continuous precipitation becomes lager with the aging time increasing. Secondary deformation can inhibit the progress of discontinuous precipitation and promote continuous precipitation, causing the strength enhanced obviously.