Microstructure And Properties Of Cu-0.4%Cr-0.12%Zr-0.01%Si Alloy With High Strength And Conductivity

The microstructure,morphology,size of the precipitates and the orientation relationships with the Cu matrix in the as-cast Cu-0.4%Cr-0.12%Zr-0.01%Si alloy were investigated.Different states of precipitation strengthened Cu-0.4%Cr-0.12% Zr-0.01%Si alloy were prepared by a combination of both the cold drawing and heat treatment.After sufficient research on Cu-0.4%Cr-0.12%Zr-0.01%Si wire,the process to get the excellent performance of the alloy was obtained.The effect of heat treatment and cold drawing on the microstructure and the properties of the wires were investigated.Moreover,the related properties of the Cu-0.4%Cr-0.12%Zr-0.01%Si contact wires were compared with the current Cu-Sn and Cu-Mg contact wires.There are four phases in the as-cast Cu-0.4%Cr-0.12%Zr-0.01%Si alloy,which are Cu matrix,pure Cr,Cu₅Zr and Cr₃Si.The Cr₃Si particles have smaller size and diffusive distribution than the Cr particles in the Cu matrix.This implies that the addition of Si constituent can result in the refinement of Cr precipitation.The mechanical properties for the aged alloy without solution treatment are higher than those for the alloy with solution treatment and aging because there can be a more excellent combination of both dispersion strengthening and work hardening in the aging process for the alloy without solution treatment.If the as-cast Cu-0.4% Cr-0.12%Zr-0.01%Si alloy drawn toη=1.8 is directly aged at 500℃for 1 h and then drawn toη～3.8,the tensile strength and relative electrical conductivity can reach 600 MPa and 84.8%IACS,respectively.At large draw ratios(η=3.8),the microstructure develops into filamentary morphology which significanltly changes the properties.The work-hardening exponent of the wires after heat-treatment is smaller than the wires without heat-treatment at the same draw ratio.The pile-ups of the dislocations around the precipitates and the incoordinate strain between the precipitate and Cu grain will increase the strength and elastic modulus of the alloy.As the draw ratio increases from 3.8 to 5.6,the tensile strength and the strain hardening exponent rise slowly because of the interaction between the dislocation and precipitate dominates the strain hardening behavior.As the draw ratio increases from 5.6 to 8.8,the tensile strength and the strain hardening exponent rise rapidly because of the interaction between the interface and precipitate dominates the strain hardening behavior.The analysis of the fracture morphology for the Cu-0.4%Cr-0.12%Zr-0.01%Si alloy in tensile test indicates that the ductile fracture changes gradually to brittle fracture as the draw ratio increases.The ultimate tensile strength and the thermal softening resistance of the Cu-0.4%Cr-0.12%Zr-0.01%Si contact wires are significantly higher than those of current Cu-Sn and Cu-Mg contact wires.The Charpy impact toughness of Cu-0.4%Cr-0.12%Zr-0.01%Si alloy,whether at room temperature or at -40℃,is significantly higher than that of Cu-Sn or Cu-Mg alloy.The three alloys fail to show the brittle-transition phenomenon in the impact toughness tests from ambient temperature to -40℃.The conductivity of the Cu-0.4%Cr-0.12%Zr-0.01%Si alloy is only about 7%lower than that of the Cu-Sn alloy,but significantly higher than that of Cu-Mg alloy.