Transmission Electron Microscopy Observations on Cu-Mg Alloy Systems

Abstract

Environmentally friendly Cu-based alloys with high strength and low electrical resistivity have been much sought in order to replace deleterious Cu-Be alloys for electrical applications. As one of the candidate systems, we have examined age-hardening behaviors of Cu-Mg alloys by using transmission electron microscopy (TEM). Cu-2.26wt.%Mg alloys were solution-treated and annealed at 723K, and their structural changes have been investigated. The Vickers hardness measurements showed that they aged-harden gradually. Our TEM observations showed that annealing for 6h brings about precipitation of numerous needle-like particles of 10 nm in length. The diffraction studies indicated these precipitates consist of the Cu2Mg phase with {111}Cu habit planes. When annealed for 96h, these precipitates become semi-coherent, which was manifested by moiré fringes; while maintaining the orientation relationship of (111)Cu//(111)Cu2Mg, [110]Cu//[110]Cu2Mg.