Effects of Cr Addition on the Precipitation and Properties of Cryo-Rolled CuNiSi Alloys

Abstract

CuNiSi alloys are widely used for lead frames and connectors due to the combination of high strength and high electrical conductivity. In this work, the microstructures, properties and precipitation behaviors of cryo-rolled CuNiSi alloys with different Cr additions were investigated. The results show that the microstructures of cryo-rolled CuNiSi alloys are mainly composed of nano-sized deformation twins. During aging, discontinuous precipitation gradually takes the place of continuous precipitation with the onset of recrystallization. The addition of chromium reacts to form Cr3Si particles and facilitates the formation of lamellar structures in the cryo-rolled states of CuNiSi alloys. Moreover, both the recrystallization and the discontinuous precipitation of cryo-rolled CuNiSi alloys are hindered by the addition of Cr elements. As a result, the mechanical strength of cryo-rolled CuNiSi alloys after aging can be maintained. The best combination of properties obtained in the CuNiSi-0.15Cr alloy is 761 MPa, 6.1% and 48.4% IACS in ultimate strength, elongation and electrical conductivity, respectively.