Evolution of microstructure and properties of an ultrahigh strength Cu–Ni–Sn alloy with low Sn content during the multi-stage thermomechanical treatment

Abstract

An ultrahigh strength Cu–9Ni-1.5Sn-0.8Si-0.1Al alloy was designed. The effect of multi-stage thermomechanical treatment on the evolution of the microstructure and the properties of designed alloy is explored. The alloy treated by cold rolled (60%)-pre-aging (400 °C/30 min)-cold rolled (50%)-450 °C/120 min-cold rolled (50%)-330 °C/120 min had a tensile strength of 1150 MPa and remained electrical conductivity of 18.1 %IACS. Nanoscale β′-Ni3Sn, β-Ni3Si, γ′-Ni3Al precipitates formed during the thermomechanical treatment. The Cu matrix and precipitates maintain an orientation relationship (OR) were [111]Cu//[111]p and [200]Cu//[200]p. More than half of the ultra-high strength of the design alloy is contributed by precipitation strengthening. The multi-stage thermomechanical treatment further improves mechanical and electrically conductivity properties of Cu–Ni–Sn alloy compared to the single-stage aging treatment. The synergistic impact of nanoparticles formed on heat treatment and dislocations formed on deformation further promoted the precipitation of Ni3X (X = Sn, Si, Al) in the matrix.