Abstract
It is well known that during a pre-precipitation process in which the formation of Guinier-Preston zones takes place, an increase of resistivity at its early stage, followed by a decrease, occurs in a number of age-hardenable aluminium-base alloys. Recently we have experimentally determined the contribution of the G.P. zones to the electrical resistivity and it has been shown that the scattering power due to a G.P. zone increases with its size.
The object of the present paper is to investigate in detail the influence of size and shape of G.P. zones on the scattering power. The electrical resistivity, the Hall coefficient and X-ray small-angle scattering measurements have been performed for several Al-Zn alloys aged for 1000 min at 20, 60 and 110°C. The value of the electrical resistivity and the Hall coefficient were analyzed in order to obtain the relaxation times due to a G.P. zone scattering by using the two-band model with the aid of the size distribution of the zones.
It is shown that the scattering power of a G.P. zone increases with its size, but this rate changes at the zone size of about 10 Å. The change seems to result from the shape change of the G.P. zone.
