A set of extrusion samples of Al-Si-Mg alloys (0.5 wt%Mg and 0.3-0.8 wt%Si)
were, respectively, T1- and T4-heat-treated. Differential scanning calorim
etry (DSC) was used to heat the samples to particular temperatures to promo
te the formation of precipitates for study by transmission electron microsc
opy (TEM). It was found that, apart from beta ", beta', and B', there were
many precipitates showing rectangular lattices when viewed along the long a
xes of the precipitates. It is considered that the residual stresses (or di
slocations) in the extrusion after the TI-treatment facilitated the nucleat
ion and growth of the precipitates during the heating in the DSC. (C) 2001
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