Electrodeposited HEDP-based ultrafine-grained CuAg alloy foils with ultra-high strength and high conductivity

Copper‑silver (Cu Ag) alloy foil has become a key material in the electronics and electrical sectors owing to its high electrical conductivity, excellent thermal dissipation properties, and favorable mechanical characteristics. To overcome the inherent trade-off between strength and conductivity in pure copper foil, this study employed a cyanide-free pyrophosphate-hydroxyethylidene diphosphonic acid (HEDP) mixed-ligand electrolyte to fabricate Cu Ag alloy foils with an ultrafine-grained structure via the electrodeposition method. An orthogonal experimental design was employed to optimize the process, and the effects of silver alloying and current density on the microstructure, mechanical properties, electrical conductivity, and corrosion behavior were systematically investigated. Research indicates that at pH = 10, temperature = 40 °C, and a current density of 0.7 A·dm −2 , alloy foil containing 8.78 wt% silver exhibits an ultra-high tensile strength of 1148 MPa, electrical conductivity of 71.8% IACS, and outstanding corrosion resistance. This is attributable to the addition of silver, which significantly refines the grain structure, suppresses twinning formation, promotes strong Cu(220) texture, and enhances surface smoothness and hydrophobicity. Microstructural analysis confirms a supersaturated solid solution with nanoscale Ag-rich second-phase particles. The ultra-high strength arises from the synergistic effects of grain refinement and solid solution strengthening. Electrochemical analysis indicates that the co-deposition is a diffusion-controlled, irreversible process following a three-dimensional instantaneous nucleation mechanism, as indicated by chronoamperometry fitted with the Scharifker-Hills model. This work provides a viable fabrication route and theoretical foundation for developing cyanide-free copper-based alloy foils with high strength, high conductivity, and excellent surface quality.