Enhancing the comprehensive properties of as-cast Cu–Ni–Si alloys by continuous extrusion combined with subsequent thermomechanical treatment

Abstract

Producing high-strength and high electrical conductivity Cu–Ni–Si alloys from as-cast state to thin strips is a challenging issue in the industry, as high-temperature homogenization, multi-step rolling, and aging processes are frequently employed and, any mistakes in each step can affect the quality of the product. In the present study, the comprehensive properties of an as-cast Cu–Ni–Si alloy were improved by a short process, i.e., continuous extrusion combined with rolling and aging processes, without homogenization treatment. The results indicated that both the mechanical and electrical properties of the alloy at the optimized route were dramatically enhanced. A final microstructure containing fine grain sizes, massive precipitates, and dislocations was obtained, thus contributing to high tensile strength (763 MPa), high electrical conductivity (49.6% IACS), and good ductility (5.8% fracture elongation). The strengthening mechanisms were then quantitively calculated. The results showed that the dislocation strengthening, grain boundary strengthening, and precipitation strengthening take 25.2%, 16%, and 51.2% of the total yield strength, respectively. It has also been found that there are two sizes of precipitates and both were identified to be δ1-Ni2Si. Although the volume fraction of the fine Ni2Si is small, it contributes to a large portion of the yield strength. Hence, there is great potential to control the precipitate size to enhance the strength of the Cu–Ni–Si alloy further for this combined technique.