The structure of the “influenced grain boundary region” of an Al‐12at.% Zn alloy in dependence on quenching conditions

Abstract

AbstractIt is known that in the AlZn alloys the nucleation and growth of the G.P. zones during isothermal ageing in the RT‐range considerably depend on the applied quenching treatment and often certain “irregularities”, e.g. an inversion of the decomposition rate with increasing homogenization temperature (Tq), are observed. Various conceptions were developed in order to explain these inversions, but none of them can consistently interpret the observed main features. For more details see Siebert and Kroggel et al. It is of interest for the present work to mention that various models were developed to explain the structure of the precipitation free zone (PFZ). They are mainly based on suggesting that the profile of the vacancies or that of the solute atoms or both in the GB‐region determine the width and the structure of the PFZ (see e.g. Synecek et al.).It was the idea of the authors to gain more information on the effect of the GB on the structure changes proceeding in its vicinity on investigating not only the width and structure of the PFZ, but the details of the structure changes occurring from the regions very close to the GB up to the midgrain in dependence on various quenching conditions (Tq and quenching rate, vq).For this reason we selected an Al‐12at.%Zn alloy produced from materials of purity 4N and aged the samples of thickness 0.12 mm, after various quenching treatments, at 100 °C for 1 h in order to attain precipitates suitable to be determined in size sufficiently accurately. The samples were annealed at Tq = 300 °C or 490 °C for 0.5 h, quenched to RT into water, fluid W250, or oil, stored at RT for 10 s, and finally aged at 100 °C for 1 h. The foils investigated in the TEM of type TESLA BS 540 operating at 120 kV were electrolytically thinned by the well‐known window method.