Increase in the Strength and Electrical Conductivity of a Cu–0.8Hf Alloy after Rotary Swaging and Subsequent Aging

Abstract—The structure, electrical conductivity, and mechanical properties (including fatigue strength) of a Cu–0.8% Hf alloy after rotary swaging (RS) at various strains and subsequent aging are investigated. RS is shown to cause the formation of a microstructure elongated in the deformation direction. When the strain increases, the average grain width decreases and grains acquire an increasingly elongated shape. After RS at ε = 2.77, the formation of an ultrafine-grained structure with an average subgrain size of 173 ± 12 nm is observed inside the elongated grains. When the strain increases, the strength of the alloy increases and the plasticity decreases. Subsequent aging causes an increase in the strength of the quenched alloy and the alloy after RS at ε = 0.58 and 1.39; hardening is absent after RS at ε = 2.77. In all cases, aging increases the electrical conductivity of the alloy as a result of the decomposition of a supersaturated solid solution and the precipitation of the Cu5Hf phase. The best combination of the mechanical and functional properties is achieved after RS at ε = 2.77 and subsequent aging at 475°C for 2 h: the ultimate tensile strength is 461 ± 28 MPa, the ductility is 12.5 ± 2.4%, the fatigue limit is 325 MPa, and the electrical conductivity is 90.4 ± 1.9% IACS.