Effect of Ni and Si Contents on Age–Precipitation in Cu–Ni–Si Alloy Having Ni/Si=2

Abstract

Cu–Ni–Si alloys have been used for electronic devices such as semiconductor lead frames because Cu–Ni Si alloys have excellent balance of electrical conductivity and strength. It is well known that Cu–Ni–Si alloys are strengthened by fine precipitates of δ–Ni₂Si (orthorhombic crystal structure) during aging treatment. There are many reports about mechanical properties of Cu–Ni–Si alloys, however, a few papers are dealt with crystal structure evolution of both matrix and precipitates using high resolution transmission electron microscope (HRTEM) .

In this work, 4 kinds of Cu–Ni–Si alloys, 31NS alloy, 42NS alloy, 53NS alloy and 74NS alloy having Ni/Si＝2, were prepared and hardness test and microstructure observation of those 4 alloys were performed to investigate the effect of Ni and Si content on age–hardening behavior and microstructure. In as quenched samples, coarse or fine intermetallic compounds were remained in all alloys. They are mostly identified as δ–Ni₂Si by scanning electron microscope–energy dispersive X–ray spectroscopy (SEM–EDS) technique. In aged samples, fine precipitates were confirmed by TEM and HRTEM observation, and they are mostly identified as δ–Ni₂Si. Fine precipitates increased with increasing of Ni and Si content.