Pre-precipitation rate in Al-10% Zn alloy neutron irradiated at 78°K

An examination of the analysis by Schüle concerning the enhanced Guinier–Preston formation, observed by Ceresara et al. (C-F-P), in Al–4·4 a/o Zn after neutron irradiation at 78°K has been made. Schüle concluded that the vacancy concentration after irradiation was insufficient to account for the enhanced zone formation and that interstitials were responsible for the enhancement. The result of the present examination, which utilizes the actual numerical values of the C-F-P experiment, reveals that the vacancy concentration after the irradiation was more than adequate to account for the observed G.P. zone formation. In addition the enhanced zone formation after the irradiation at 78°K by C-F-P and after fast neutron irradiation of Al–Zn alloys at 4·5°K by the author are in complete agreement with the enhanced zoned formation observed in quenching experiments. Therefore, it is proposed that the motion of vacancies is responsible for the enhanced G.P. zone formation after irradiation as well as after quenching.