Study On Copper Base Alloy Prepared By Aluminum Thermal Reduction-the Secondary Refining Method

Copper-chromium alloy has high strength,high hardness,good electrical conductivity and thermal conductivity,which is used as preferred materials of high-power and high-voltage vacuum switch contacts.However,the existing methods of powder metallurgy,infiltration and vacuum auto-electric arc remelting method all use high purity copper powder and chromium powder as raw materials.The Cu-Cr alloy is usually prepared by pressing billet,and sintering or melting under high vacuum/high purity protective atmosphere,which has defects of complex processes and high cost.After more than 20 years of systematic research,the research group develops the fourth generation preparation technology of preparing homogeneous high density copper-chromium contact materials by using aluminum pyrolytic-slag refining method with copper oxide,chromium oxide and aluminum powder as raw materials,which successfully prepares copper-chromium alloy ingot with uniform composition,small grains and high density.This article is based on the previous studies,by analyzing the microstructure and strength of CuCr25 and CuCr40 alloys before and after heat treatment,using a 1OkV simulated vacuum interrupter to evaluate the electrical properties of the prepared CuCr25 and CuCr40 contact materials;and using electrical performance evaluation results as a guide to further study the effect of adding alloy components on the microstructure and properties of Cu-Cr alloyThe main contents of thesis and research results are as follows:First,the microstructure and strength of CuCr25,CuCr40 alloy before and after heat treatment were systematically analyzed.Heat treatment will lead to the precipitation and growth of Cr in the alloy.With the increase of Cr content in the alloy,the trend of Cr precipitation becomes more and more obvious.Compared with Cr size in the CuCr25 alloy,the grain size of Cr in the CrCr40 alloy increases more evidently with a trend of agglomeration during the heat treatment.Second,the electrical properties of the prepared CuCr25,CuCr40 as contact materials were evaluated by using a 10kV simulated vacuum interrupter.The CuCr alloy contact prepared by the aluminum thermal reduction-slag preparation mothod has good properties of resistance to voltage capability,impact resistance,interception ability and anti-welding ability.The voltage withstand capacity is about 70kV,higher than the rated power voltage of 42kV.Impact resistance arrives 160kV,much higher than the rated impulse voltage of 85kV.Cut-off current value before heat treatment is 0.40A,far less than the standard 3.5A.The welding force is about 190N,which meets the standard of industry 100?200N.However,the heat treatment deteriorates the impact resistance,fusion resistance and interception ability of the prepared CuCr contact materials.Therefore,compared with the traditional preparation method,the copper-chromium alloy contact material can be prepared without heat treatment process by the aluminum thermal reduction-slag refining method.But the copper-chromium contact material prepared by the method needs further improvement in breaking capacity.Then,based on the results of electrical property evaluation,in order to improve the breaking capacity of the CuCr contact materials,a new idea of adding in-situ alloy elements is proposed in this paper.In the process of aluminum thermal reduction,the alloy component is directly added by the in-situ reduction of the corresponding oxide of the alloy component.The effects of the addition of Nb,Co,Si,Fe and other alloy elements on the microstructure of CuCr alloy were systematically investigated.The results show that the addition of a small amount of Si can refine the grain.If the addition amount is too high,it will deteriorate the microstructure and properties of CuCr alloy,which is not good for the improvement of the electrical properties.With the increase of Nb content,the Cr phase particles became coarse,and the addition of Nb reduces the solid solubility of Cr in Cu.The addition of Co can improve the wettability between Cu and Cr phases and the solid solubility of Cu and Cr,which leads to the improvement of the compactness,the grain refinement and the electrical properties of the alloy.With the addition of Fe,the grain size of the Cr phase in the alloy is significantly refined,meanwhile the solubility of Cr in the Cu phase is significantly increased.The distribution of Cr in the alloy is more uniformly dispersed and the electrical properties of the alloy are also promoted.Finally,based on the addition of Fe in in-situ reduction,a new method of direct preparation of low cost and high performance CuFe alloy under low-temperature slag by using aluminum pyrolytic reduction-slag refining and using copper oxide,iron oxide and aluminum powder as raw materials is to preliminary explore.The results show that the batch addition of aluminum for thermal self-propagation can significantly improve the yield of the alloy.The appropriate reduction of the aluminum ration in the ingredients can significantly reduce the aluminum residue in the alloy.Slag refining can effectively eliminate the pores and oxide inclusions in the CuFe alloy to prepare a dense and uniform alloy ingot.