A study of Guinier-Preston zones in aluminium-copper alloys using the weak-beam technique of electron microscopy

Abstract

The weak-beam technique of electron microscopy has been used to investigate plate-like G.P. zones in aluminium-copper alloys. For aluminium-1-48 and 3-97 wt% copper alloys aged at 80, 100 and 130°C, G.P. (I) zones of about 35 to 100 Å in diameter were observed. In dark-field images, using the (002) reflection with |s| ⋍ 0-45 to 1-1 × 10⁻² Å⁻¹ the zones appeared as pairs of bright lines, the separation of which depends on the magnitude of [s]. Similarly in alloys containing G.P. (II) zones, the images showed pairs of bright lines with a slightly wider separation than the G.P. (1) zone images, sometimes accompanied by a series of closely spaced fringes. The pairs of bright lines were interpreted as corresponding to individual G.P. (I) and (II) zones by comparison with computed image profiles. The experimental images are in good agreement with images computed for a model having a displacement field corresponding to a circular edge loop lying on the habit plane of the G.P. zones, with a Burgers vector equal to 0.2_o, where а_o, is the lattice parameter of aluminium. These results are compared with Gerold's model of G.P. zones.