| Electric contact material is the key device to control the on-off of the circuit.It is vulnerable to the failure from welding,corrosion,wear and other forms in the process of repeated opening and closing.Therefore,the electric contact material needs to have strong resistance to welding,good corrosion resistance,appropriate hardness,stable and low contact resistance.Therefore,electrical contact materials have various requirements for the performance of materials,and some properties contradict others,such as good corrosion resistance,which need to add the second phase component to the material to make up alloy,but the contact resistance of the alloy is large.Therefore,in practical application,the electric contact materials need to be selected in various properties.In the process of using electrical contact materials,the performance of the material surface determines the performance of the material,so it is a common method to prepare electrical contact materials by preparing a layer of coating with good corrosion resistance,high hardness and wear resistance on the surface.However,the physical properties of the coatings prepared by traditional methods on the surface of metals are quite different from substrates,and the coating is easy to crack due to friction and wear.The potential difference between the exposed substrate and the coating surface will cause galvanic corrosion and accelerate the failure of the material.Therefore,in this paper,by means of electroplating and heat treatment,a layer of thermal diffusion coating is obtained on the surface of copper substrate,which can increase the bonding force between the coating and the substrate and reduce the potential gradient from the surface of the material to the substrate,so as to reduce the risk of galvanic corrosion of the material.Silver metal has the highest conductivity and good corrosion resistance,so it can meet the requirements of corrosion resistance and wear resistance of electrical contact materials by electroplating silver on the surface of copper matrix and forming a diffusion layer of silver and copper after heat treatment.This paper explores electroplating and heat treatment process and research material properties under the corresponding conditions,the main work and conclusions are as follows:(1)Through the thermogravimetry analysis of the silver-plated copper matrix and the comparison of the phase diagram of the Ag-Cu,it can be seen that the eutectic melting of the silver-copper alloy takes place at about780 ℃.At this temperature,the silver copper alloy is melted and precipitated in the proportion of Cu28.1% and Ag71.9%.Therefore,based on the eutectic temperature point,800℃ and 850℃ above the eutectic temperature and 700℃ and 750℃ below the eutectic temperature are selected for heat treatment.Through the analysis of the surface morphology,cross-section morphology and cross-section composition of the sample after heat treatment,it can be seen that during the heat treatment under the eutectic temperature point,with the extension of heat treatment time,the sample surface takes some small grains as the core,absorbs the nearby grains,starts to grow,and the surface roughness increases.When heat treatment is carried out above the eutectic temperature point,the eutectic melting begins at the interface of silver and copper.With the extension of time,the eutectic pool expands to the surface of the sample and the surface appears solidification morphology.Through the scanning and composition analysis of the sample cross section,it is found that the diffusion degree of silver and copper increases with the increase of heat treatment temperature and the extension of heat treatment time.After heat treatment at 750℃ for 24 hours,copper atoms diffuse to the sample surface.After heat treatment at 850℃ for 24 hours,the concentration of copper atoms in the whole coating is about 6%.At the same time,the thickness of the sample surface coating increases and the final thickness is stable about 35μm,the silver coating melted completely and the molten pool reached the saturation state at 850℃.(2)The properties of the samples are obtained by electrochemical test,hardness test,friction and wear test,conductivity test after heat treatment.It is found that with the increase of heat treatment temperature and the extension of heat treatment time,the diffusion of copper atoms in the samples is more sufficient,and the corrosion resistance and conductivity of the samples is worse.The corrosion current density of pure silver is0.87μA/cm-2,but it is 12.13μA/cm-2 after heat treatment at 850℃ for 24 hours,which is twice the corrosion current of pure copper 5.88μA/cm-2.The conductivity of pure silver was 102.38% IACS,but after heat treatment at 850℃ for 24 hours,the conductivity decreased to 31.56%IACS.However,with the increase of thermal diffusion degree,the defect concentration of the samples in the coating increases,so the hardness of the coating increases,the highest hardness is about 190HV0.01,which is about 60% higher than that of pure silver.At the same time,the wear resistance of the samples increased.Under the same conditions,the weight loss of the samples after heat treatment at 850℃ for 24 hours was only25% of the pure silver samples.In conclusion,this paper establishes the relationship between the diffusion degree of silver and copper and the properties of samples by studying the relationship between the heat treatment process and the properties of materials.In general,with the increase of heat treatment temperature and the extension of heat treatment time,the diffusion degree of silver and copper in the coating increases,the corrosion resistance and conductivity of the coating decrease,but the hardness and wear resistance of the coating increase.At the same time,the amount of silver in the material can be reduced by electroplating and thermal diffusion treatment,which has a very good practical significance for the areas where silver reserves are not rich enough.According to the application under different working conditions,the appropriate electrical contact materials can be obtained by choosing different properties. |
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