Study On Refining Process Of High-Density CuCr Alloy Prepared By Aluminum Thermal Electromagnetic Melting

CuCr alloy has the advantages of high strength,hardness,good electrical and thermal conductivity,etc.It has become the first choice for high-power vacuum high-voltage switch contact materials.At present,the industrial preparation methods of CuCr alloys mainly include powder metallurgy,infiltration and vacuum arc melting.The above processes have the disadvantages of complicated process,high production cost and low yield.Based on this,after more than 30 years of research,the research group successfully developed the fourth-generation technology prototype based on aluminothermic reduction-electromagnetic refining-castingwater vapor composite cold preparation of homogeneous copper-chromium alloys,and successfully prepared CuCr25 and CuCr40 alloys.The actual research found that the Cr segregation loss during the electromagnetic refining and casting process is the direct cause of the low Cr content in the alloy.Therefore,the purpose of this paper is to investigate the suppression of Cr segregation loss during refining and casting by appropriate refining process parameters,and to achieve the preparation of CuCr50 high-Cr dense alloy ingots.The effects of microstructure,alloy properties and heat treatment process conditions on the alloy structure and properties are systematically investigated.The main research contents and conclusions are as follows:First,the single-factor experimental design was used to study the electromagnetic melting refining process,and the influence of refining temperature,refining time,slag type and solidification cooling method on the quality of refined alloy ingots was investigated.The results show that:CuCr50 alloy directly prepared by aluminothermic reduction-electromagnetic melting casting has many defects such as porosity and oxide inclusions.Induction electromagnetic refining and casting can obviously eliminate defects such as porosity and inclusions and improve alloy quality.With the increase of the temperature of electromagnetic refining,the porosity of the alloy after refining and casting is significantly reduced,and the density is significantly increased.At the same time,the Cr phase grains are more uniformly distributed,and the hardness and electrical conductivity of the alloy are improved.Prolonging the electromagnetic refining time is beneficial to the removal of pores and inclusions in the alloy,but excessively long refining holding time will cause segregation and loss of the Cr component in the alloy.Refining slag is conducive to the removal of oxide inclusion defects in the alloy,but it is not conducive to the removal of porosity inclusions in the alloy;water-vapor composite condensation solidifies the microstructure uniformity and the Cr phase particle size refinement in the alloy.Therefore,suitable electromagnetic refining conditions are:the refining temperature is 1850?,the refining time is 90 minutes,no slagging agent is added,and water vapor is condensed and solidified.The density of the alloy sample prepared at this time was 7.96 g/cm3,the porosity was only 0.88%,the hardness was 97.2 HB,and the electrical conductivity was 10.43 MS/m.Then,the copper-chromium alloy directly prepared by aluminothermic reduction electromagnetic casting was subjected to solution heat treatment,and the influence of solution temperature and solution time on the microstructure and properties of the alloy were investigated.Solution treatment can disperse the Cr phase in the CuCr50 alloy and form a precipitated phase.At the same time,the solid solubility of Cr in the Cu matrix increases,and the microscopic pores in the alloy tend to decrease.As the solution temperature increases,Cr The solid solubility in Cu matrix also tends to increase.When the solution temperature is 950?,the Cr phase is uniformly distributed and the grain diameter is small.When the solution temperature is as high as 1000?,a clear dendritic Cr phase begins to appear in the alloy,and the Cr phase tends to agglomerate.With the increase of solid solution time,the solid solubility of Cr phase in Cu matrix increases.When the solution time is 100 min,the alloy has obvious dendritic crystals,and the Cr phase grains are obviously aggregated.The suitable solid solution process conditions are:solid solution temperature is 950? and holding time is 80 min.At this time,the Cr phase distribution of CuCr50 alloy is the most uniform,the solid solubility of Cr in Cu matrix is increased to 2.06%,and the conductivity is 9.68 Ms/m,hardness is 98.9 HB.Finally,aging heat treatment was performed on the copper-chromium alloy after solution treatment,and the effects of aging temperature and aging time on the microstructure and properties of the alloy were investigated.After the aging treatment,the solid solubility of Cr in the Cu matrix was significantly reduced.Compared with the aging treatment,the electrical conductivity of the alloy increased,but the hardness decreased.When the aging temperature is increased from 450? to 500?,the electrical conductivity and hardness of the alloy are increased;when the aging temperature is further increased to 550?,the hardness of the alloy is further increased,but the electrical conductivity of the alloy is decreased.The aging temperature is 500?,the aging time is 2 h,the hardness of the alloy is 82.1 HB,and the electrical conductivity is 10.25 Ms/m;when the aging time is 3 h,the alloy hardness is 89.5 HB,and the electrical conductivity is 14.61 Ms/m;the aging time is 4 h,The Cr phase particles began to agglomerate and overaged.The hardness of the alloy further increased to 95.7 HB,but the electrical conductivity decreased to 11.68 Ms/m.The suitable solution heat treatment process conditions are as follows:solution temperature is 950?,holding time is 90 minutes,aging temperature is 500?,and aging time is 3 h.The final CuCr50 alloy ingots were prepared by using the determined appropriate electromagnetic refining process conditions and heat treatment process conditions.The mass fraction of Cr is 48.45%,the density is as high as 7.96 g/cm3,and the relative density is as high as 99.18%.The conductivity of CuCr50 alloy is 15.16 MS/m,and the hardness is 104.7 HB.