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E. Povoden-Karadeniz, P. Warczok, P. Lang, A. Falahati, E. Kozeschnik:
"A thermodynamic model of Guinier-Preston-zones in the Al-Mg-Si system";
Talk: Calphad XXXIX, Jeju, Südkorea; 2010-05-23 - 2010-05-28.

Precipitation hardening in Al-Mg-Si alloys is of great importance for the development of heat-treatable materials with outstanding mechanical properties. In particular metastable low-temperature precipitates govern the mechanical properties of these materials. Thermodynamic modeling of these metastable phases is demanding due to lack of experimental equilibrium data.
General agreement exists that the sequence of metastable precipitates in 6016 Al-Mg-Si alloy during continuous heating after previous solution treatment and quenching can be simplified as solute clusters GP (Guinier-Preston)-zones ´´´. A thermodynamic description of metastable GP-zones is presented that is based on a critical assessment of available first-principles data, as well as estimations of the thermodynamic solvus that were based on experimental information on the dissolution temperature of GP-zones.
Up to now the generally accepted model for early GP-zones is adopted from [1] proposing Mg-Si layers in Al-matrix with Mg:Si=1:1. On the contrary, the new model is based on an ordered Al3Mg1 L12 structure as evident from experiments [2]. Employing a four substitutional sublattice description for ordering, this model allows a simultaneous reproduction of microstructural, thermodynamic and chemical findings. The new thermodynamic model of GP-zones is successfully applied to kinetic simulations of precipitation sequences in 6016 Al-alloys.
Stacking of L12-substructures has also been proposed as a reliable mechanism of GP-zones formation in other systems, for instance Al-Cu [3], and the application of the presented approach in other systems is thus promising.