PRECIPITATION AND DISSOLUTION PROCESSES IN AGE-HARDENABLE AL-ALLOYS - COMPARISON OF POSITRON-ANNIHILATION AND X-RAY SMALL-ANGLE SCATTERING INVESTIGATIONS .1. AL-ZN(3 AT-PERCENT),AL-ZN(4.5 AT-PERCENT),AL-ZN(6 AT-PERCENT),AL-ZN(10 AT-PERCENT),AND AL-ZN(18 AT-PERCENT)

Peak height measurements of the angular correlation curve of 2γ‐positron annihilation radiation (PAS) as well as X‐ray small‐angle scattering investigations (XSAS) are performed during continuous heating of supersaturated Al—Zn alloys applying vH = 0.5 K/min. From XSAS results information on decomposition process (Guinier radius, mean distance of Guinier‐Preston zones, and integral intensity) are obtained. Strong evidence for positron trapping by GP zones is given. The peak height curves show a good correlation with the course of the integral intensity of XSAS as well as with stable and metastable phase diagram lines. For Al alloys having Zn content of 4.5 at% or more almost all positrons are trapped by GP zones. From the PAS measurements a Zn concentration of (72 ± 5) at% within the zones is estimated. The dissolution of precipitate is reflected in the peak height by a rapid increase of about 10%. For the lowest concentrated alloy (3 at% Zn) from both, PAS and XSAS measurements indications on the formation and growth of zones are found during the first stage of heating. The strong positron interaction with GP zones is mainly caused by the difference of positron affinity of Al and Zn atoms. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA