Cu segregation around metastable phase in Al-Mg-Si alloy with Cu

Abstract

Cu distribution around Q′-phase in an Al-1.0 mass% Mg 2Si-0.5 mass% Cu alloy has been investigated by the analytical transmission electron microscope (TEM), energy-filtering TEM (EFTEM), and high angular annular dark field scanning TEM (HAADF-STEM) techniques in order to determine the effect of Cu on the precipitation of this alloy. Cu- segregation around rod-shaped precipitates in the sample aged at 523 K for 24 ks was confirmed by energy dispersive X-ray spectroscopy, elemental maps, and HAADF-STEM images. Cu-segregation was also detected from small precipitates, which show a hexagonal network with a lattice constant of 1.04 nm in their HRTEM images. Coarse rods show homogeneous distribution of Cu, and chemical composition is similar to that of coarse Q′- or Q-phase. Small precipitates less than 10 nm were also confirmed in as-quenched samples, and those precipitates seem to form during quenching. © 2007 The Japan Institute of Metals.