Etude cristallographique de la phase de transition M'' dans Al–8%Zn–1%Mg

The structure of the transition phase M′ in AlZnMg alloys has been studied by Buerger X-ray precession photographs and transmission electron microscopy. The M′ phase, also called η′ or R, has a hexagonal or pseudo-hexagonal cell with a = 4.96, c = 14.03 Å. It is confirmed that M′ precipitates are hexagonal platelets with the following epitaxy: (00.1)_M′//(111)_Al and |10.0|_M′//10|_Al. It is shown that none of the known models of the unit cell accounts for the observed scattered intensities.