Development of gradient structured copper wire deformation and heat treatment technology for cable industry

Abstract This study addresses the challenge of optimizing the trade-off between strength, ductility, and electrical conductivity in high-strength microcomposite Cu-14Fe alloy wires. A novel thermo-mechanical processing approach is proposed, combining successive cycles of twisting in an equal-channel step die with subsequent drawing along two temperature routes: cold (Route A, room temperature) and warm (Route B, 250 °C), followed by low-temperature annealing (300–500 °C). Results demonstrate that cold processing induces a sharp gradient microstructure (from submicron grains ~ 400 nm at the surface to 7 μm in the center), yielding maximum hardening. Conversely, warm deformation activates dynamic recovery, forming a uniform polygonized structure that preserves ductility. It was found that deformation processing along Route A ensures maximum workpiece hardening (ultimate strength σ в = 675 MPa), while warm deformation along Route B allows for the retention of an increased ductility resource δ = 19.0%, ψ = 25.0%. An anomalous change in mechanical properties was revealed during subsequent thermal treatment: annealing at 400 °C initiates a simultaneous increase in strength and ductility for both routes, achieving peak σ в values of 700 MPa (Route A) and 610 MPa (Route B). A key finding is an anomalous simultaneous increase in both strength and ductility during post-deformation annealing at 400 °C for both routes, driven by precipitation hardening from the decomposition of the supersaturated solid solution. Ultimately, preliminary warm deformation (Route B) proves technologically superior, establishing a thermally stable subgrain structure with enhanced resistance to softening and restrained recrystallization kinetics across the investigated temperature range.