Effects of Amounts of Additive Elements on Microstructure and Mechanical Properties of Heavily Cold–Rolled Cu–Ni–Si Alloys

Abstract

Heavily cold–rolled Cu–Ni–Si alloys with low concentrations of Ni and Si were aged at relatively low temperatures and the changes in the microstructure and properties were systematically investigated. Heterogeneous–nano structure was inhomogeneously developed as well as a typical low–angle lamellar structure in all the alloys by the cold rolling. The evolution of the heterogeneous–nano structure, which induced grain subdivision, was more evident in the alloys with higher contents of Ni and Si. The alloy with added largest amounts of additive elements exhibited highest tensile strength with moderate ductility, i.e., good balance of mechanical properties. However, it showed early softening because of lower thermal stability owing to finer grain size, Therefore, full–ageing seemed to be difficult. Even while rather good mechanical properties were attained by the combination of heavy cold rolling and low–temperature ageing of Cu–Ni–Si alloys with low concentrations of Ni and Si, it was revealed that a suitable ageing condition is highly required for the further improvement of their properties.