Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

In Situ Structural Characterization of Ageing Kinetics in Aluminum Alloy 2024 across Angstrom-to-Micrometer Length Scales



Fan Zhang, Lyle E. Levine, Andrew J. Allen, Carelyn E. Campbell, Adam Abel Creuziger, Nataliya Kazantseva, Jan Ilavsky


The precipitate structure and precipitation kinetics in an Al-Cu-Mg alloy (AA2024) aged at 190 °C, 208 °C, and 226 °C have been studied using ex situ TEM and in situ synchrotron-based, combined ultra-small angle X-ray scattering, small angle X-ray scattering, and wide angle X-ray scattering across a length scale from sub-Angstrom to several micrometers. TEM brings information concerning the nature, morphology, and size of the precipitates and the latter provides qualitative and quantitative information concerning the time-dependent size and volume fraction evolution of the precipitates at different stages of the precipitation sequence. Within the experimental time resolution, precipitation at these ageing temperatures involves dissolution of nanometer-sized small clusters and formation of the planar S phase precipitates. Using a three-parameter scattering model constructed on the basis of TEM results, we established the temperature-dependent kinetics for the cluster-dissolution and S-phase formation processes. These two processes, while occurring simultaneously, have different kinetic rates, with the cluster-dissolution rate approximately double the S-phase formation rate. We also identified a dissolution activation energy at (149.5 ± 14.6) kJ mol-1, which translates to (1.55 ± 0.15) eV/atom, as well as an activation energy for the formation of S precipitates at (129.2 ± 5.4) KJ mol-1, i.e. (1.33 ± 0.06) eV/atom. The SAXS/WAXS results show the absence of an intermediate GPB2/S" phase in the samples under the experimental ageing conditions. These results are further validated by precipitation simulations that are based on Langer-Schwartz theory and a Kampmann-Wagner numerical method.
ACTA Materialia


Al-Cu-Mg alloys, precipitation kinetics, microstructure characterization, thermodynamic modeling, in situ synchrotron X-ray scattering


Zhang, F. , Levine, L. , Allen, A. , Campbell, C. , Creuziger, A. , Kazantseva, N. and Ilavsky, J. (2016), In Situ Structural Characterization of Ageing Kinetics in Aluminum Alloy 2024 across Angstrom-to-Micrometer Length Scales, ACTA Materialia, [online],, (Accessed May 19, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created May 31, 2016, Updated October 12, 2021