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On the Influence of Short R.T. preageing on the formation of the η′‐phase in an Al‐Zn(4.5 at.%)‐Mg(2.5 at.%) alloy
Author(s) -
Radomsky M.,
Löffler H.
Publication year - 1980
Publication title -
kristall und technik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0023-4753
DOI - 10.1002/crat.19800150612
Subject(s) - nucleation , quenching (fluorescence) , precipitation , alloy , phase (matter) , homogeneous , electrical resistivity and conductivity , materials science , atmospheric temperature range , thermodynamics , crystallography , analytical chemistry (journal) , chemistry , metallurgy , fluorescence , chromatography , physics , meteorology , organic chemistry , quantum mechanics
The influence of short R.T. preageing (1 min) after quenching from 480 °C into RT‐water on the formation of the η′‐phase in an Al‐Zn(4.5)‐Mg(2.5) alloys has been investigated by means of TEM, XSAS, resistivity, and hardness measurements in the ageing temperature range between T a = 120 °C comparing samples directly quenched (DQ) to T a and those quenched into RT‐water, kept there for 1 min, and subsequently stored in an oil‐bath of T a (IQ). At T a ≦ 170 °C both heat treatments result in finely distributed precipitates of the η′‐phase accompanied by a fairly high hardness value. But at T a ≧ 180 °C the DQ leads only to few coarse heterogeneously formed η′‐ and η‐precipitates, whilst the IQ yields qualitatively the same precipitation structure as already described at T a ≦ 170 °C even till 280 °C. These results are interpreted assuming that. A1) the limitation temperature of homogeneous formation of η′ is located at about T h = 175°c and A2) during the pre‐ageing at RT “nucleation sites” are formed as already suggested by RYUM, which are able to act as sites for heterogeneous formation of η′ even at T a > T h . Hints are obtained that the formation of these “nucleation sites” is not so strongly governed by the quenched‐in excess vacancies as discussed in the literature.