A metastable phase diagram has been constructed for the Al-Zn-Mg alloy system in the 1-4. 5 at. % Zn and 1-3 at. % Mg concentration range. The following metastable phase boundaries were determined: the upper temperature limit of GP zone formation, GP//F, And of eta prime formation, eta prime //F, the highest temperature up to which the eta prime phase can exist in the matrix, eta prime s, the boundary for homogeneous-heterogeneous nucleation of the eta prime phase, eta prime //F//H and finally, the temperature at which GP zones formed during long-term RT aging dissolve, i. e. , the zone solvus for RT GP zones, GPs. It was found that the phase boundary of homogeneous-heterogeneous eta prime nucleation intersects the solvus line for RT GP zones at a temperature of 160 degree C and a Zn concentration of 2. 5 at. %. From this it was concluded that if the Zn content of an alloy is less than 2. 5 at. % the GP zones formed at RT dissolve completely during reversion before considerable eta prime formation can take place.
|Number of pages||6|
|Publication status||Published - Jan 1 1979|
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