| As development of the science and technology, it needs the higher performance of Cu-Ag alloy, which has a high strength and high electrical conductivity. This paper is financially supported by National high-tech R&D Program of China (863Project)(No.2007AA03Z519). Based on the coarse and non-uniform solidified structure problems in Cu-Ag ingot, it is necessary to research the micro structure and properties of Cu-Ag alloy with the horizontal magnetic field, high magnetic field (HMF) and electromagnetic stirring (EMS). It is necessary to make use of the horizontal magnetic field, HMF and EMS to control the solidification processing and improve the solidified structure quality, then the optimized as-cast structure will be prepared for the cold drawing. In other words, the properties and microstructures of Cu-Ag wires by cold drawn are also researched to reveal the new method to improve the alloy properties under the magnetic field.The effect of horizontal magnetic field on the solidified structure under the different direction of the temperature gradient shows that when the magnetic field direction is perpendicular to the temperature gradient, the magnetic field has better refinement effect on the dendrite and eutectic. The effect of the horiziontal magnetic field on the vertical directional solidified structure and properties shows that the magnetic field can refine Cu dendrites and eutectics obviously, and it leads the increasing of the Ag content in the pro-eutectic Cu dendrite too. It maybe related to the thermo electromagnetic convection (TEMC) which has the effect on the undercooling and the nucleation of Cu dendrite. The XRD results show that the easy magnetized direction of Cu axial is<111>, and the intensity of Cu<111> peak increase under horizontal MF.The effect of HMF on the as-cast solidified structure shows that the primary and secondary dendrite are refined under12T HMF, moreover, the eutectics are coarser and the Ag content in Cu dendrite is higher under HMF. It indicates that the HMF has influenced the Cu dendrite nucleation, consititual undercooling and the solutes diffusion. The hardness results show that hardness of the alloy decreases under HMF.The effect of EMS on the as-cast solidified structure and samples’hardness shows that the grains become thinner with increasing Ag content. Furthermore, the grains are refined under EMS apparently. The pro-eutectic Cu dendrites become shorter and coarser, and the eutectic becomes coarser too. It indicates that the effect of the EMS on the dendrite fracture mechanism and the solute solid distribution are the main factors that change the dendrite morphology and eutectic structure. The hardness results show that the hardness increases the with increasing of the Ag content, meanwhile, the transverse section hardness increases but the longitudinal section hardness decreases in EMS samples. Results of different EMS parameters effect on the as-cast solidified structure and properties of Cu-6%Ag alloy show that the grains become more and more thinner with the increasing of the EMS current and frequency, meanwhile, the pro-eutectic dendrites change from the thinner dendrites to the petal shape euquiaxed dendrites and the spherical grains with increasing of the EMS intensity. The hardness results show that the hardness is higher in thinner equiaxed dendrites, and it decreases in coarser petal equiaxed dendrites, but it begins to increase in spherical grains. The electrical conductivity is lower in thinner euquiaxed dendrites, but it increases in coarser petal equiaxed dendrites. Moreover, it begins to increase in spherical grains too.The effect of cold drawing on the Cu-Ag alloys treated with and without HMF show that the as-cast net structure changes into filaments structure during drawing process on longitudinal section, meanwhile, the filaments size and spacing decrease with the increasing of the cold drawing strain. As to HMF wires, the thickness of the filaments seems coarser than them in without HMF samples, moreover, the Ag precipitates filaments seems coarser and sparser too. The effect of cold drawing process on the Cu-Ag alloys treated with and without EMS show that the filaments thickness becomes coarser, and the filaments spacing increases in EMS samples. The XRD results show that the dendrites grow randomly and disorderly in EMS sample in the as-cast condition, however, the<111> direction of Cu dendrites rotates to the drawing direction by cold drawing deformation.The properties of HMF wires show that the ultimate tensile strength (UTS) increases with the increasing of the cold draw strain, but the plastic decreases correspondingly. However, as the Ag content increasing to25%, both of the UTS that the conductivity decreases with the increasing of the cold strain. At lower deformation stage, the HMF samples have lower electrical conductivity, but as the increasing of the cold drawing strain, such as η>5.6, the conductivity of Cu-25%Ag wire treated with HMF is higher. The properties of EMS wires results show that the properties of Cu-25%Ag wires are better. As to the Cu-25%Ag wires in EMS, the UTS is lower than that of the NEMS samples as the η<3.9, but the UTS of the EMS sample begins to increase higher than the NEMS sample as the η>3.9. The electrical conductivity results show that the Cu-25%Ag wires in EMS sample have higher conductivity as the η＜1.9; The EMS wires have lower conductivity as the η>1.9. The results of the strength and electrical conduction mechanism show that the Ag elements, such as the solid solution and precipition in pro-eutectic Cu dendrites are the important factors on the strength and the conduction, moreover, the grain size also plays the important effect on the Cu-Ag alloy. The calculation of the electrical resistivity model shows that the solid solution and precipitation of Ag in pro-eutectic Cu dendrites are the main factors which determine the electrical resistivity in lower drawing strain stage, but the interface and filament size are the main factors that determine the electrical resistivity in higher drawing strain stage. |
PDF Full Text Request