Transmission Electron Microscopic Observation of a Novel Al3Zr-η′ Core-shell Particle in Al-Zn-Mg-Cu Alloy

Abstract

The Al₃Zr-η′ core-shell particles were observed in the Al-12Zn-2.4Mg-1.1Cu-0.5Ni-0.2Zr alloy using high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). Two types of Al₃Zr particles appear in the Al matrix: one is a standalone Al₃Zr particle that is coherent with the matrix, and the other is an as-core Al₃Zr particle acting as a nucleation site of the η′ precipitates, resulting in a core-shell particle which is semi-coherent with the matrix. The shell is composed of η′ precipitates with four variants. The strain in the as-core Al₃Zr is lower than that in the standalone Al₃Zr, and a considerable amount of strain exists across the interfacial regions between the η′ precipitates and the matrix.