Microstructure and Properties of a Cu-Ni-Sn Alloy Treated by Two-Stage Thermomechanical Processing

The effects of two-stage thermomechanical processing on the microstructure and properties of Cu-15Ni-8Sn-1.0Zn-0.5Al-0.2Si alloy have been investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and mechanical and electrical property testing. Spinodal decomposition and beta-Ni3Sn precipitates with L1(2) ordering structure appeared in the preaged alloy. The crystal orientation relationships between the copper matrix and beta-Ni3Sn precipitates were (200)(Cu)parallel to(100)(beta), [001](Cu)parallel to[001](beta) and (220)(Cu)parallel to(110)(beta), [112](Cu)parallel to[112](beta). The high strength of the studied alloy can mainly be attributed to the combined effects of precipitation strengthening and substructure strengthening. The interaction between the nascent nanoparticles that form during pre-aging and the dislocation configurations that form during cold rolling promotes precipitation in the matrix and suppresses formation of cellular precipitates and coarse precipitates at grain boundaries, improving the comprehensive properties of the alloy. The peak-aged alloy treated with two-stage thermomechanical processing showed hardness of 387 HV, electrical conductivity of 8.5% IACS, tensile strength of 1176 MPa, yield strength of 1106 MPa, elongation of 3.86%, and strength-ductility product of 4539 MPa%.