Investigation On Preparation,Microstructure And Properties Of Cu-Cr-Zr-Mg Alloys

Owing to the combination of high strength and good electrical conductivity,Copper alloys have been widely used in the field of lead frame engineering.The representative series are Cu-Cr-Zr series alloys,which belong to aging-strengthened Cu alloys,and their alloy properties can be further improved by micro-alloying.In this project,Cu-Cr-Zr-Mg alloy was prepared by adding a small amount of Mg element and vacuum induction melting method.The effect of the addition of Mg on the microstructure and properties of the Cu-Cr-Zr alloy was studied.Cu-Cr-Zr-Mg alloy was prepared by pouring and cooling with a fine-diameter copper mold.Compared with the furnace cooling,the effect of different cooling methods on the microstructure and properties of the alloy was studied.The samples after solution treatment were subjected to different degrees of cold rolling deformation,and the effect of deformation on the microstructure of the alloy was analyzed.The aging treatment was performed on the alloy with 40%deformation,and the effect of the aging method on the room temperature mechanical properties of Cu-Cr-Zr-Mg alloy was further discussed.The main results are as follows:（1）The as-cast microstructure of Cu-Cr-Zr-Mg alloy cooled in the furnace wereα-Cu dendrite and（α+β）Cu-Cr eutectic phase.With the addition of Mg element,the alloy structure was significantly refined and secondary dendrite arm spacing was significantly reduced which maade the hardness of the alloy increased and the conductivity decreased continuously.When the Mg content achieved 0.45wt%,the hardness of the alloy reached a maximum of 54.8HB,and the electrical conductivity reached a minimum of 36.1%IACS.（2）After solution aging treatment of Cu-Cr-Zr-Mg alloy,a dispersedly distributed Heusler phase Cr Cu₂（Zr Mg）were formed on the matrix,thereby greatly improved the conductivity and hardness of the alloy.Among them,the Cu-1.0Cr-0.25Zr-0.3Mg alloy maintained the better comprehensive performance,and its electrical conductivity and hardness reached 79.2%IACS and 138.3HB.（3）The Cu-1.0Cr-0.25Zr-0.3Mg dendrite obtained by cooling with the copper mold was significantly refined,the SDAS value was reduced by more than half,and the eutectic phase region was significantly reduced.The solid solubility of alloying elements in the copper matrix increased significantly,and the distribution was more uniform.Compared with the furnace cooling,the hardness of the alloy increased by 28.5%,and the electrical conductivity was decreased.（4）The Cu-Cr-Zr-Mg alloy prepared by using the copper mold is subjected to solution aging treatment,and the precipitated phase were more dispersed and fine,which further improves the alloy performance.When the Mg content was 0.3wt%,the electrical conductivity and hardness of the alloy were 156.9HB and 80.8%IACS,respectively.The tensile properties of the alloy were significantly improved,the size of the dimples was reduced,and the tensile strength was increased by 20.7%compared with the furnace cooling,reaching 451.8MPa.（5）Copper mold cooling Cu-Cr-Zr-Mg After cold-rolling deformation,the crystal grains changed from polygonal shape to fibrous shape,and the hardness of the alloy matrix was greatly increased under the action of work hardening and the electrical conductivity was reduced.When the deformation of the alloy achieved 40%,after aging treatment,the nano-scale Cr Cu₂（Zr Mg）phase and Cr phase were dispersed and precipitated along the dislocations.The hardness and conductivity of the alloy were maintained at a balanced state,respectively 166.2HB and 82.7%IACS.The tensile strength was increased by 24.8%compared with the undeformed aging alloy.After 60%deformation and aging treatment,the grains of alloy were recrystallized and growed.（6）After 40%cold-deformed Cu-Cr-Zr-Mg alloy was subjected to two-stage aging treatment,compared with single-stage aging alloy,the hardness was increased by 15.6%,the electrical conductivity was increased by 19.5%,and the tensile strength of the alloy was as high as559.7MPa.Cold deformation single-stage aging treatment reduced the plasticity of the alloy due to the work hardening phenomenon,the size of the dimples at the fracture of the alloy and the depth were reduced.After the two-stage aging treatment,the plasticity of the cold deformed alloy has rebounded.