Abstract
Al-Zn alloys containing 0.84∼4.4 at%Zn were studied by the measurement of electrical resistivity and small angle scattering of X-ray. The results may be summarized as follows: (1) After isothermal aging below a certain temperature, the electrical resistivity of each alloy increases initially, reaches a maximum value and then decreases corresponding to the formation and growth of G.P.zones. But when isothermally aged above a certain temperature, the electrical resistivity shows a slight increase in a short time (about 30 sec) and then decreases very slowly for a long time, with no distinct maximum in the isothermal aging curves. In this case, it seems that G.P.zones are not formed and the small increase of electrical resistivity is related to some behaviour of supersaturated zinc. Therefore, these certain temperatures seems to be the maximum temperature at which G.P.zones can be formed in Al-Zn alloys. (2) The quantity of zinc consumed for the formation and growth of G.P.zones may be proportional to the difference between the total atomic concentration of zinc and the atomic concentration which can be estimated from the solvus for G.P.zones at the aging temperature. (3) Reversion was incomplete when aged for a long time. (5) Plots of time, tM, required to reach the maximum resistivity against the reciprocal of absolute temperature are approximated by a straight line at lower temperatures. But tMs are fairly longer than that expected from the extension of a straight line at higher temperatures. The plots cannot be approximated by a straight line in a wide temperature range. These phenomena might be explained as follows: The quantity of zinc consumed for the formation and growth of G.P.zones decreases rapidly as the aging temperature rises.
