H. W. Zandbergen, ^* S. J. Andersen, J. Jansen

Precipitation hardening, in which small particles inhibit the movement of dislocations to strengthen a metal, has long been used to improve mechanical strength, especially of aluminum alloys. The small size of precipitates and the many possible variants of the orientation relation have made their structural determination difficult. Small precipitates in commercial aluminum-magnesium-silicon alloys play a crucial role in increasing the mechanical strength of these alloys. The composition and structure of the " phase in an aluminum-magnesium-silicon alloy, which occur as precipitates (typically 4 nanometers by 4 nanometers by 50 nanometers) and are associated with a particularly strong increase in mechanical strength, were determined. Element analysis indicates that the composition is Mg₅Si₆. A rough structure model was obtained from exit waves reconstructed from high-resolution electron microscopy images. The structure was refined with electron nanodiffraction data (overall R value of 3.1 percent) with the use of a recently developed least squares refinement procedure in which dynamic diffraction is fully taken into account.

H. W. Zandbergen is at the National Centre for High Resolution Transmission Electron Microscopy (HREM), Laboratory of Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, Netherlands. S. J. Andersen is at the National Centre for HREM, Laboratory of Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, Netherlands, and Senter for Industriell og Teknisk Forskning Applied Physics, 7034 Trondheim, Norway. J. Jansen is at the National Centre for HREM, Laboratory of Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, Netherlands, and the Laboratory for Crystallography, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, Netherlands.
^*   To whom correspondence should be addressed.

Volume 277, Number 5330, Issue of 29 August 1997, pp. 1221-1225
©1997 by The American Association for the Advancement of Science.