Influence of Cryogenic High–Speed Rolling on Tensile Strength and Electric Conductivity of Cu–Ni–Si Alloy Sheet

Abstract

Cu–2.3%Ni–0.55%Si （mass%） sheets, which had been aged at 723K after solution treatment at 1173K or 1273K, were subsequently processed by either （a） low–speed rolling （LSR） （5 m/min at RT） or （b） cryogenic high–speed rolling （C–HSR） （1500 m/min at 77K）. The total reduction in thickness of 78% was applied in 3–pass operation. Mechanical properties, electrical conductivity, and microstructure of the as–rolled sheets were investigated. The LSRed sheet showed tensile strength of 731 MPa and electrical conductivity of 27.9%IACS, while the C–HSRed sheet showed 822 MPa and 26.2%IACS. The C–HSRed sheets contains more deformation twins and shear bands in the microstructure than the LSRed sheet. Using a modified Hall–Petch equation, it is recognized that the higher strength of the C–HSRed sheet is attributed to fine–grained microstructure and increased dislocation density.