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E. Povoden-Karadeniz, P. Warczok, P. Lang, A. Falahati, M. Ahmadi, E. Kozeschnik:
"Thermodynamic Modeling of Guinier-Preston-zones in the Al-Mg-Si System";
Talk: ISMANAM 2010, 17th International Symposium on Metastable, Amorphous and Nanostructured Materials, Zürich; 2010-07-04 - 2010-07-09.

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 rule the mechanical properties of these materials.
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 ´´´. Thermodynamic modeling of these metastable phases is demanding due to lack of experimental equilibrium data.
We present a new thermodynamic description of metastable GP-zones. The generally accepted model for early GP-zones is adopted from [1] proposing Mg-Si layers in Al-matrix with Mg:Si=1:1. Alternatively, layering of Mg-Si can be obtained by considering Al-Mg-Si GP-zones an fcc-based L10 ordered structure with the chemical formula Al4Mg2Si2. Ternary GP-zones are thus modeled by choosing a symmetric four substitutional sublattice description, which allows fcc-based L10 and L12 ordering. The new model is founded on the parameter optimization of binary endmember compounds with available first-principles data, as well as experimental thermal stabilities of truly existing metastable Al3Mg that exhibits L12-structure [2,3]. With this approach, available thermodynamic data as well as chemical compositions of GP-zones can be well reproduced, and the thermal stability of ternary GP-zones appears reliable. The practical applicability of the new model has been validated in kinetic simulations of precipitation sequences in 6016 Al-alloys.
Solute monolayers resulting from L10 ordering and stacking of ordered substructures might be characteristic also for GP-zones in other Al-base alloys. The application of the presented model to GP-zones of other systems is thus promising.