| Cu-Ag alloys are widly used as electrical,thermal,and key structural components in many fild such as electronic information,electrical,energy,machinery,aerospace,rail transit,and national defense,due to its excellent electrical,thermal and mechanics properties.In the past few decades,although researchers have carried out a lot of research work on oxidation performance and strength properties of Cu-Ag alloys,there are still problems such as complex material preparation processes,unstable oxidation resistance,and inability to synergistically improve strength and conductivity,which is difficult to meet the application requirements with the continuous development of science and technology.In view of the above problems,based on the influence of heat treatment process on Ag precipitation behavior,systematically studies the influence law and mechanism of Ag precipitation behavior on the conductivity,oxidation resistance and mechanical properties of Cu-5 wt.%Ag alloy.The aging treatment process used to control the microstructure,and then synergistically controls the electrical conductivity,oxidation resistance and mechanical properties of Cu-5 wt.%Ag alloy are realized.The main conclusions of this article are summarized as follows:(1)The effects of aging and deformation on the precipitation behavior,microstructure,electrical conductivity and hardness of Cu-5 wt.% Ag alloy are studied.The microstructure of rich-Ag phase and Ag/Cu interface are revealed from the atomic sacle.Low-temperature aging is more conducive to discontinuous precipitation of rich-Ag phase,and high-temperature aging and crystal defects caused by cold deformation are conducive to promoting continuous precipitation of rich-Ag phase.The interface of richAg precipitates inside the crystal grain and Cu matrix is a semi-coherent structure with a cube-on-cube orientation relationship;When rich-Ag phase precipitates at twin boundary,there is a Cu(111)// Ag(111)heterogeneous twin semi-coherent structure with Cu matrix,showing a straight interface and step interface;when the rich-Ag precipitates at the ordinary grain boundary,it has a semi-coherent structure with a misorientation with the Cu matrix.This study provides a theoretical basis for the study of the macroscopic properties of Cu-Ag alloys.(2)Based on the results of Ag precipitation behavior,a threedimensional mesh structure of rich-Ag phase continuously precipitated along the grain boundaries is obtained by high and low temperature combined aging process.The effect of rich-Ag phase on the oxidation resistance of Cu-5 wt.%Ag alloy and its mechanism are studied.The results show that the oxidation rate of the aged Cu-5 wt.% Ag alloy is much lower than that of the solution treated alloy.This is because Ag precipitated along grain boundaries forms a semi-coherent interface with Cu matrix,which reduces the free energy of the grain boundary,effectively inhibit the preferential oxidation of grain boundaries;Meanwhile,the rich-Ag phase can effectively increase the diffusion activation energy and decrease the diffusion rate of O and Cu atoms at grain boundaries.Thus,significantly enhance the oxidation resistance of the alloy.This research has taken an important step towards the wide application of high conductivity and oxidation resistant Cu-Ag alloys.(3)The effects of particle size on the Ag precipitation behavior,oxidation resistance property of the Cu-5wt.%Ag alloy powders on surface and near surface area are studied.The results indicated that the precipitation of Ag mainly through grain boundary and surface diffusion during the low temperature aging treatment(250 ℃).Due to the higher surface diffusion driving force,surface diffusion coefficient and solid solubility of smaller-sized powders,the precipitation rate of rich-Ag phase is much faster than that of larger-sized powders.This is because Ag is mainly precipitated through grain boundary and surface diffusion at low temperature,and smaller powder have.As the temperature increases,volume diffusion takes up an increasingly important role,and the influence of particle size on the precipitation behavior of Ag on the powder surface gradually weakens.The oxidation resistance of the powder is closely related to the amount of Ag precipitated on the surface of powders.When rich-Ag phase precipitates along grain boundaries of powder surface and formes a three-dimensional grid structure,the oxidation resistance of the alloy powder can be effectively improved.This study is of great significance for enriching and perfecting the precipitation behavior of Ag in Cu-Ag alloy powder and its anti-oxidation theory.(4)The effects of deformation heat treatment on the microstructure,mechanics and electrical conductivity properties of Cu-5 wt.%Ag alloys are studied.The results indicated that,deformation can greatly improve the mechanical properties of the alloy;and heat treatment is beneficial to improve the electrical conductivity of the alloy.When the alloy undergoes repeated deformation and heat treatment,the mechanical properties and electrical conductivity of the alloy can be improved synergistically.The hardness and ultimate tensile strength of the alloy after three deformations reached 160.753 HV and 538.8 MPa,respectively,and the electrical conductivity reached 92.4% IACS.This is related to the effect of the precipitated phase pinning the dislocations,inhibiting the recovery and recrystallization process of the alloy,increasing the nucleation sites of the Ag precipitates,and promoting the continuous precipitation of the Ag phase.This study provides a new idea for the preparation of high strength and high conductivity Cu-based alloys. |
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