| High strength and high electrical conductivity copper alloys have been widely used in electric,electronic,transportation and machinery manufacturing industries,and the most typical applications are railway contact wire and integrated circuit lead frame.According to the sequence,the evolution of high strength and high conductivity copper alloys can be divided into three stages,namely Cu-Fe-P alloy system,Cu-Ni-Si alloy system and Cu-Cr-Zr alloy system.Among these alloy systems,Cu-Cr-Zr alloys have the most excellent properties and development prospect.Therefore,in this paper,we chose Cu-Cr-Zr alloy as the research object,and investigated the influence of Zr element on Cu-Cr alloy.By optimizing the rolling and aging treatment process synergistically,we have fabricated high strength and high electrical conductivity Cu-Cr-Zr alloy plates with a desired combination properties of tensile strength(>600 MPa)and electrical conductivity(>80% IACS).In this paper,by comparing the microstructures and properties of Cu-Cr alloy and Cu-Cr-Zr alloy,we drawed the following conclusion: Zr element can refine the grain size of Cu-Cr alloy observably and change the morphology and size of Cr-riched phases.For example,the grain size of solutionized Cu-Cr-Zr alloy decreases 55%,compared with solutionized Cu-Cr alloy.With the addition of Zr element,the size of Cr-riched phases decreased obviously,and the morphology of them transformed from strip-type to sphericity.In particular,a core-shell structure with the shell of Zr and the core of Cr was discovered in Cu-Cr-Zr alloy;this structure can hinder the coarsening of Cr-rich phases and modify the shape of Cr-rich phases,and thereby strengthen the copper matrix.Due to the modification of the size and morphology of Cr-riched phases,the Cu-Cr-Zr alloy had a higher tensile strength than the Cu-Cr alloy,while the Cu-Cr alloy had a lower microhardness and wear resistance than the Cu-Cr-Zr alloy.A new technology,including a two-stage cryorolling(liquid nitrogen temperature rolling)and an intermediate aging treatment,was proposed to fabricate the Cu-Cr-Zr alloy plates.The average twin/matrix lamellar thikness of the rolled sample is 37 nm,which decreases nearly 55% and 38% compared with that of the room temperature rolled and cryorolled samples.After aging at 450 °C for 60 min,the Cr-riched phases in the sample fabricated by the new process are much finer and more dispersive compared with those of the other two processes.The suructure composed of nano-scale deformation twins and precipitates was observed,which can strengthen the Cu matrix obviously.The samples containing deformation twins,core-shell structure and nano-scale precipitates fabricated by the new technology have a higher tensile strength,microhardness and wear resistance compared with the other two processes,which are attributed to the interactions of grain boundaries strengthening,twin boundaries strengthening,precipitation strengthening and strain hardending.The results show that a desired combination of the tensile strength(650 MPa)and electrical conductivity(79.83% IACS)were obtained after aging at 450 °C for 60 min,and a desired combination of the tensile strength(614 MPa)and electrical conductivity(82.23% IACS)were obtained after aging at 475 °C for 60 min. |
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