The influence of Mg content on the formation and reversion of Guinier-Preston zones in Al-4.5 at % Zn-x Mg alloys |
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Authors: | G Honyek I Kovács J Lendvai Ng-Huy-Sinh T Ungár H Löffler R Gerlach |
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Affiliation: | 1. Institute for General Physics, Loránd E?tv?s University, Budapest, Hungary 2. Section of Mathematics and Physics, Pedagogical University, Halle, Germany
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Abstract: | The influence of Mg concentrations on the dissolution of Guinier-Preston (GP) zones formed at room temperature (RT) and on
the formation of more stable phases has been investigated during continuous heating of Al-4.5 at % Zn-xMg alloys. The Mg content was varied from 0.05 to 3 at %. After different aging periods at RT, calorimetric investigations
were carried out at heating rates of 40 and 80° C min−1. In the case of alloys with a lower Mg content (x ⩽ 0.5 at %) only the dissolution of GP zones could be observed during the heating, whereas in the case of alloys with a higher
Mg content the formation of theη′-phase started before the total dissolution of GP zones and at higher temperatures the formation of theη-phase also took place. These phases were identified by transmission electron microscopy. The heat-of-solution of GP zones
shows saturation as a function of RT aging time. The time needed for the saturation increased monotonously with increasing
Mg content. The reversion of zones was followed byin situ X-ray small angle scattering measurements. The change of the total scattered intensity was measured during continuous heating
at a rate of 40° C min−1. These investigations have confirmed the results of the calorimetric measurements which indicate that the total dissolution
of zones takes place only in the case of the alloys with a Mg content lower than 0.5 at %. In the case of alloys with a Zn
concentration of 4.5 at % studied here, 1 at % Mg is sufficient to initiate the formation of more stable phases during the
reversion of zones.
On leave from Hanoi University, Vietnam. |
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