A quantitative interpretation of the decomposition kinetics of some AlZnMg alloys

Abstract

The decomposition behaviour of some binary AlZn(Y) and ternary AlZn(3)Mg(X) and AlZn(6)Mg(X) alloys in the early stage of ageing are studied by means of resistivity measurements using the times of the beginning (tBR) and the end (tER) of the straight line of the Rln ta‐curve and the well known maximum of resistivity (tmaxR). It is shown that the experimental results can be explained by the extended jump model assuming that in the time interval considered the growth of the GP zones is mainly determined by the diffusion of zincvacancy pairs, the rearrangement effect of the quenched‐in vacancies to the thermodynamic equilibrium valid at the ageing temperature, and the additional capture effect of the vacancies in the GP zones caused by the Mg atoms built‐in the zones. The rearrangement effect probably takes place at about tBR. The fact that tBR and tER decrease whereas tmaxR increases with rise of Mg content is discussed also.