Study On Non-Vacuum Melting Process And Properties Of Cu-Cr-Zr Alloys

Copper alloys have been widely applied in many fields for their good mechanical properties and excellent conductive properties. With the rapid development of science and technology, the performance of copper alloys also put forward higher requirements, as a typical aging-strengthening alloy, Cu-Cr-Zr alloy met the requirements of high strength and high electrical conductivity.Because of the severe burning loss of Cr and Zr during smelting, nowadays Cu-Cr-Zr alloy was prepared by vacuum melting process which has confined its application greatly. The theoretical analysis of melting process was discussed in this paper from thermodynamic and dynamic aspects. Cu-Cr-Zr alloys were melted under non-vacuum conditions and the effects of heat treatment process on alloys'properties were discussed in the research.The melting characteristics were discussed and the Gibbs free energy changes of some reactions were calculated in the paper. According to this, the possibilities of the relevant reactions were estimated by theΔG TΘand the evaporation, diffusion and gas inhaling process were analyzed from dynamic aspect. The calculations showed that chromium and zirconium could react with N2, O2, C and Cu2O at the melting temperature. Zirconium could react with crucible materials such as SiO2 and Al2O3, but not MgO, so it was suggested that magnesial furnace lining should be used during smelting. The burning loss of elements was controlled by diffusion. As the melting temperature and partial pressure of reactive gas increased, the gas inhaling also increased, so the smelting of Cu-Cr-Zr alloys should be protected by inert gas.Crucibles of different materials were used in melting Cu-Cr-Zr alloys under non-vacuum conditions. The ingots had good surface quality and no macro-defects inside. The effects of crucible material, melting atmosphere and melting time on element absorptivity were dicussed. The results further validated the theoretical analyses of melting process.The as-cast structure of Cu-0.77Cr-0.45Zr alloy was observed by scanning electron microscope(SEM). The energy spectrum analysis and surface scanning showed that dendritical Cr appeared in matrix alloy, and Zr existed in grain boundary mainly in the form of compounds. The effects of deformation and aging parameters on properties of Cu-0.77Cr-0.45Zr alloy were analyzed. The results showed that along with the aging process, the solute atoms precipitated from copper matrix constantly, the microhardness and electrical conductivity were improved obviously. It was concluded that deformation, aging temperature and time had influence on strengthening effect, the tensile strength, microhardness and electric conductivity of Cu-0.77Cr-0.45Zr alloy could be increased to 546MPa, 170HV and 76%IACS by 60% cold deformation before aging at 500°C for 2h.