Effect of Thermo-Mechanical Treatment on Electrical Conductivity and Strength of Cu-0.29 mass%Zr Alloy Wires

In our previous study, a thin wire of a Cu-0.29 mass%Zr alloy produced by repeated intermediate annealing during rolling and wire-drawing (IA wire) exhibited a 0.2% proof stress, sigma(0.2), of 600 MPa, an ultimate tensile strength, sigma(u), of 630 MPa, and an electrical conductivity, E, of 91.7%IACS. A thin wire of the alloy produced by ECAP-conform processing and subsequent rolling and wire-drawing (ECAP wire) showed larger values of sigma(0.2) = 730 MPa and sigma(u )= 790 MPa but a smaller value of E = 73.0%IACS than the IA wire. This study investigates the causes of the lower value of E and the higher value of sigma(0.2) of the ECAP wire, and the higher value of E of the IA wire. The higher value of sigma(0.2) of the ECAP wire is attributed to its smaller grain size and higher dislocation density. The lower value of E of the ECAP wire is primarily attributable to the fact that newly found, ordered face-centered cubic (fcc) precipitates having a cube-on-cube orientation relationship to the Cu matrix in the alloy produced by the ECAP-conform processing were cut by dislocations during rolling and wire drawing, resulting in dissolution in the Cu matrix. The IA wire showed the higher value of E because recrystallization by repeated intermediate annealing changed all the fcc precipitates into incoherent fcc precipitates that were not cut by dislocations. Further, based on the obtained results, an attempt was made to fabricate thin wires of the alloy having good strength, ductility and electrical conductivity. All the fcc precipitates in the alloy were made incoherent with the Cu matrix by utilizing recrystallization after sufficient precipitation. Then the alloy was processed by ECAP and subsequently wire-drawn. The fabricated thin wire exhibited higher values of sigma(u) = 820 MPa, epsilon(t) = 4.0% and E = 86.9%IACS.