Simulation of the electron diffraction patterns from needle/rod-like precipitates in Al-Mg-Si alloys

The origin of the selected area electron diffraction (SAED) patterns from needle/rod-like metastable precipitates embedded in alpha-Al matrix in Al-Mg-Si alloys have been studied via an example of beta '' phase. In addition, the SAED pattern from beta '' phase has been simulated with significant improvement in comparison with the previous simulations. Three important factors, i.e. the 12 crystallographically equivalent variants of beta '' phase in the alpha-Al matrix due to the highly symmetric f.c.c. structure of alpha-Al, the coherence between beta '' phase and the alpha-Al matrix, and the double diffractions from the alpha-Al matrix and beta '' phase, are proved to contribute to the special square-shaped features in the SAED patterns from beta '' phase and thus fully taken into account in the simulation. An improved but simplified method for simulating the SAED patterns from needle/rod-like metastable precipitates has been developed. This method is further verified by simulating the SAED pattern from Q phase. The simulated SAED patterns from both beta '' and Q phases fit the experimentally determined patterns very well. (c) 2011 Elsevier Inc. All rights reserved.