Effect of cold drawing strain on the microstructure, mechanical properties and electrical conductivity of low-oxygen copper wires

Abstract

The effects of cold drawing process on the microstructure, mechanical properties and electrical conductivity of low-oxygen copper wires were studied. The results show that at low drawing strains (ε ≤ 1.23), the plastic deformation is dominated by planar slip, some of grains are rotated along the drawing direction, giving rise to a <111> texture. At medium strains (1.23 < ε ≤ 1.91), most of grains have re-oriented and laid parallel to the drawing direction, and the <111> and <100> textures are highly developed. At high strains (ε > 1.91), a fibrous structure is formed, with a staggered distribution of <111> and <100> textures. With the increase of drawing strain, the volume fraction of the <111> texture first increases and then decreases, while the volume fraction of the <100> texture increases monotonously. The yield strength first increases and then decreases, yielding the maximum value of 427.5 MPa at the strain of 1.91. Interestingly, the electrical conductivity of the copper wires changes with cold drawing strain and moves in the opposite way to the yield strength. The electrical conductivity first decreases and then increases with the minimum value at a strain of 1.91 (~87.5% IACS). At strains higher than 2.74, dynamic recrystallization occurs, resulting in a decrease in dislocation density and an increase in grain size. In addition to the dislocation density and grain size, the yield strength of the copper wires is further impacted by the texture development. The electrical conductivity is less influenced by dislocations and vacancies. Instead, it is dominated by those grain boundaries perpendicular to the drawing direction. An excellent strength-conductivity combination was achieved by tailoring the microstructure of copper wires. For example, a wire with the yield strength (YS) of 400.5 MPa and electrical conductivity (EC) of 94.3% IACS was acquired when the drawing strain reaches 2.74.