| Cu-Cr alloy has the high strength and hardness of Cr and the excellent electrical and thermal conductivity of Cu and mainly used to prepare contact materials.At present,at home and abroad the production of Cu-Cr alloys mainly adopts methods such as vacuum consumable smelting and powder metallurgy,but these methods have certain defects.After decades of research,our research group has developed the thermite reduction-electromagnetic stirring method to prepare high-density Cu-Cr alloys.This method has short process and low cost,and successfully prepared uniform composition,fine grains,and high density.The reason why Cu-Cr alloy is used as a contact material is because of its excellent comprehensive properties,but there are many factors that affect the alloy’s performance,including impurities and defects,microstructure,heat treatment process,and distribution of Cr phase.This paper studies the uniformity of the Cr phase distribution in the alloy microstructure and its influence on the properties of the alloy.The heat treatment process is used to heat treat different parts of the alloy transverse section,and studied the changes in the microstructure and properties of different parts of the alloy before and after heat treatment.Based on the previous work,this paper investigated the influence of the amount of CaO on the uniformity of the alloy structure,maintaining a unit mass of reaction heat of 3500J/g,and investigated the Al2O3·0.2CaO,Al2O3·0.3CaO and Al2O3·0.4CaO respectively.The alloy composition meets the standard and there is no segregation when the slag is Al2O3·0.2CaO.By observing the microstructure of the alloy,it is found that the Cr phase is fine,the uniformity is high,and the number of inclusions in the alloy is small.As the amount of CaO added increases the upper and lower segregation of alloy components is serious and cannot reach the national standard.The Cr phase of the upper and lower parts of the alloy is coarsely distributed and agglomerated,and the content of inclusions in the alloy increases,and the separation of slag and gold is poor.The effect of electromagnetic stirring on the structure and properties of the alloy was studied,the research found that after adding electromagnetic stirring,the alloy composition is uniform and there is no segregation phenomenon,and all can meet national standards.From the micro structure,it is observed that the Cr phase grains are fine and uniform.According to the calculation of the size of Cr phase grains in the microstructure,it is found that the size of the Cr phase grains is not more than 20um,and the density is calculated.The density of the alloy reaches the national standard ≥7.9g/cm3 at the stirring frequency of 20Hz.The electrical conductivity and hardness under different stirring frequencies are tested and found that the hardness of the alloy is higher than the national standard,and the hardness is up to 87.4HB at 20Hz,but the electrical conductivity of the alloy under that condition cannot reach the national level.Through energy spectrum analysis,it is found that there are more Cr phases in the Cu matrix to form a supersaturated solid solution,which causes the distortion of the Cu lattice and enhances the electron scattering.A comparative study of the transverse section of the alloy before and after heat treatment shows that the Cr content increases from the edge of the alloy to the middle part.After heat treatment,the large-sized Cr phase in the micro structure of the alloy was dissolved,and many finely dispersed spherical Cr particles were precipitated.Before and after heat treatment,the hardness of the alloy is directly proportional to the Cr content,and the electrical conductivity is inversely proportional to the Cr content.Before heat treatment,it was found that the lowest hardness of the alloy at the edge was 89HB,and the highest at the middle part was 93.7HB;the highest conductivity at the edge of the alloy,no matter which part could not reach the national standard.After heat treatment,it is found that the hardness of each part has been greatly improved up to 108HB.Compared to before heat treatment the average hardness of the alloy has increased by 12.4%;the electrical conductivity of the alloy has also been correspondingly improved,up to 14.9MS/m.Compared with before heat treatment,the average conductivity increased by 40.8%.The increase in alloy hardness and electrical conductivity after heat treatment is due to the solid solution and aging treatment,the supersaturated precipitation in the Cu matrix,the precipitated Cr is in the shape of fine spheres and uniformly dispersed in the Cu matrix,the main strengthening mechanism is dispersion strengthening. |
PDF Full Text Request