| Due to its excellent mechanical properties,conductivity and thermal conductivity,copper alloy has been widely used in many fields such as power,transportation,machinery,electronics,communication,information,computer,national defense and so on.However,with the development of science and technology,the requirements of copper alloys in various fields are getting higher and higher.For example,with the development of integrated circuit chips,higher requirements are put forward for conductivity,thermal conductivity and strength of lead frame materials;with the rapid development of railway,contact wires need high strength and high conductivity,and high softening temperature,heat resistance and corrosion resistance are also required.It has been proved that the Cu-Cr-Zr alloy is one of the most feasible alloy to meet the above requirements.However,the improvement of its comprehensive properties needs to be combined with processing technologies.The aging precipitation process of Cr and Zr has the greatest influence on their electrical conductivity and strength.In order to improve the properties of Cu-Cr-Zr alloy,it is necessary to study the control of solidification structure and precipitates.The application of high static magnetic field can influence the heat transfer,mass transfer and momentum transfer in the solid-liquid phase transformation process,and influence the composition distribution and microstructure of Cu Cr Zr alloy,which improve the electrical and mechanical properties of the alloy.Rare earth,as a “vitamin” in industrial production,has excellent functions of purifying melt and refining grain.It can greatly optimize the microstructure of copper and copper alloys,improving the comprehensive properties of copper alloys.In this paper,the effect of static magnetic field and rare earth Y on the directional solidification microstructure and properties of Cu-1.0Cr-0.1Zr alloy were studied.The main research contents are as follows:In the first part of this paper,the effect of drawing speed on the directional solidification structure and properties of Cu-1.0Cr-0.1Zr alloy was studied.The results showed that the microstructure undergone the changes of short cellular→long cellular→dendrite→long cellular with the increase of drawing speed.The conductivity of the alloy decreased with the increase of drawing speed,while the hardness increases.The effect of static magnetic field(0-5 T)on the microstructure and properties of the alloy were studied.The results showed that the directionally solidified microstructure changed from cellular to dendrite with the increase of magnetic flux density,and all the microstructure were dendrites at the magnetic flux density of 5 T.The electrical conductivity of the alloy increased and the hardness decreased with the increase of magnetic flux density.In the second part of this paper,the effect of Y on the directional solidified microstructure and properties of pure copper and Cu-1.0Cr-0.1Zr alloy was studied.First,Y was added into the directional solidification process of pure copper.It was found that the conductivity of pure copper increased and then decreased with the increase of Y content.When the content of Y was 0.02 wt.%,the conductivity reached the maximum of 100.32%IACS,while the hardness of the alloy decreased from 61.43 HV to 59.71 HV.The effect of rare earth Y on directionally solidified microstructure and properties of Cu-1.0Cr-0.1Zr alloy was also studied.The results showed that with the increase of the addition of Y,the directionally solidified microstructure changed from a short cellular to a long cellular and the solidified microstructure became a short cellular finally.The size of coarse Cr-rich phase decreased from 500 nm to 300 nm and the dispersed precipitated phase increased significantly when 0.06 Y was added.The conductivity of Cu-1.0Cr-0.1Zr alloy increased and then decreased with the increase of the addition of Y,while the hardness and tensile strength decreased.Cu-1.0Cr-0.1Zr-0.06 Y alloy has the best ultimate tensile strength,elongation and conductivity,which are 254.1 MPa,48% and 84.59%IACS,respectively.In the third part of this paper,the effect of different magnetic flux density(0-5 T)on the microstructure and properties of Cu-1.0Cr-0.1Zr-0.06 Y was studied.The results showed that the solidified microstructure changed from a short cellular to a long cellular with the increase of magnetic flux density,and the solidified microstructure became dendrite finally.The conductivity increased from 52.89%IACS to 68.02%IACS,while the hardness of the alloy decreased from 74.56 HV to 58.40 HV at the magnetic flux density of 5 T.In conclusion,the evolution of microstructure,composition and precipitates of Cu and Cu-1.0Cr-0.1Zr alloy were systematically studied by applying magnetic field and adding rare earth Y.It was found tha both static magnetic field and rare earth Y can significantly influence the solidification microstructure and electrical/mechanical properties of Cu-1.0Cr-0.1Zr alloy,and the related influence mechanism was discussed,which provide a reference for the preparation of higher performance,high strength and high conductivity of Cu-Cr-Zr alloy. |
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