Low-temperature decomposition of Al-Mg alloys: Guinier-Preston zones and L1₂ ordered precipitates

Abstract

Low-temperature (below 100°C) ageing experiments were performed on ice-water quenched and on slowly cooled Al-Mg alloys with 11, 14 and 16 at% Mg. Differential scanning calorimetry (DSC) generally reveals two overlapping endothermic events in the range 50-150°C which are identified to be due to the dissolution of Guinier—Preston (GP) zones and the spherically shaped L1₂ ordered β″ phase precipitates. Data on the stability limits of GP zones and β″ phase are obtained from isothermal calorimetry and DSC experiments. Our data on the solvi agree well with literature values provided that resistometry data, which are inconsistent with all other data, are not considered. Possible reasons for the unreliability of the latter are discussed and new solvus lines for GP zones and β″ phase are presented.