The Shapes of G.P. Zones in Al-Zn Alloys

Abstract

The size and shape of G.P. zones in Al-Zn alloys were studied by means of the X-ray small angle scattering technique and transmission electron microscopy, and the following results were obtained.
(1) The shape of G.P. zones was changed from spherical to ellipsoidal when their radii exceeded about 32 Å.
(2) The ellipsoidal G.P. zones had long axes which were parallel to the ⟨111⟩ direction. The dimensions of G.P. zones were 32∼35 Å in short axis and 32∼150 Å in long axis, when the specimens were aged at room temperature.
(3) The size of G.P. zones in the quenched specimens were distributed fairly uniformly, but not so in the air-cooled specimens.
(4) When heated at high temperatures, the size of G.P. zones in the aged specimens becomes larger and the shape became ellipsoidal. The sizes of ellipsoidal G.P. zones were 35∼70 Å in short axis and 150∼500 Å in long axis. But no G.P. zones were observed after heating for 2 minutes at 150°C.