High resolution electron microscopy study of Guinier-Preston (GP1) zones in Al-Cu based alloys

Guinier-Preston (GP1) zones in the model alloy Al-1.84 at.% Cu and in the industrial alloy Al-1.68Cu-1.10Mg-0.33Mn at.% (AA 2017A) were studied by means of high resolution electron microscopy. The experimental images are interpreted using multislice simulations. The majority of GP1 zones consist of atomic monolayers, the disc diameter ranging from 4 to 10 nm. In the binary alloy, double layer GP1 zones and unstable disc shaped particles on {111} planes were also found. The contrast of the GPI zones is strongly dependent on their size, on the foil thickness, on the defocus of the objective lens, less sensitive to the Cu content and much less sensitive to the position of the GP zone in the depth of the foil. (C) 1997 Acta Metallurgica Inc.