Decomposition of an Al-Mg-Cu alloy - a high resolution transmission electron microscopy investigation

Decomposition of the solid solution of an Al-3Mg-0.4Cu-0.12Si (wt.%) alloy has been studied by examining samples aged for periods of 1-16 h at a temperature of 180degreesC. High resolution transmission electron microscopy (HRTEM) was the primary method of investigation. Within the 4-16 h aging interval, nanometer scale, homogeneously dispersed, coherent, lath-like particles were detected in the matrix. The orientation of the lath particles in the matrix is such that the edges are aligned along the <100>(Al) directions. From the Fourier transformation of the HRTEM images obtained on <100>(Al) zones, it was possible to confirm that two variants give rise to diffraction spots that were previously associated with the presence of S-phase in Cu lean Al-Mg-Cu alloys. Two other variants give rise to streaked diffraction spots positioned around the (110)(Al). The detected particles are termed GPBII in this study, instead of previously suggested S-phase notation. The findings of this study are also compared with those of the frequently studied Cu rich Al-Cu-Mg alloying system. (C) 2004 Elsevier B.V. All rights reserved.