Effect of Pre-Aging Treatment on the Mechanical Properties of Cold Rolled Cu-6 wt% Ni-1.4 wt% Si Alloy

Cu-Ni-Si alloys were strengthened by Ni2Si intermetallic compound precipitation in a Cu matrix during aging. The Cu-6 wt% Ni-1.4wt%Si alloy was prepared by water quenching (solution treatment) or air cooling (homogenization treatment) after heating 980 degrees C for 2 hours and aging at 500 degrees C for 6 hours. After maintaining a high temperature single phase region, the structure of the precipitate in the matrix was changed significantly by varying the cooling rate. The solution treated aged alloy had discontinuous precipitation with fiber shaped precipitates throughout the specimen, however, the alloy with homogenization had normal spherical shaped particles. The aged alloy after homogenization treatment had higher strength, ductility and electrical conductivity, of 628 MPa, 18%, 48% IACS, respectively, than aged alloy after solution treatment, which had 582 MPa, 15.5% and 50 % IACS, respectively. In contrast to the tendency of values after aging, after rolling and a 75% area reduction at room temperature after homogenization treatment the alloy had lower strength, ductility and electrical conductivity, of 774 MPa, 10.5%, 48% IACS, than the alloy after solution treatment, with 885 MPa, 6.5%, and 48% IACS, respectively. The Cu-6 wt% Ni-1.4wt%Si alloy with fully discontinuous precipitation had lower strength and higher electrical conductivity than the counterpart alloy with normal precipitation. However, inversely, the strength increased compared to the alloy with normal precipitation after rolling with 75% area reduction, without sacrificing electrical conductivity.