ATOMIC-SCALE IMAGING AND ANALYSIS OF T' PRECIPITATES IN AL-MG-ZN ALLOYS

The composition, morphology and Volume fraction of the metastable T' p hase formed in an industrial Al-4.91wt%Mg-3.20wt%Zn alloy have been in vestigated using the tomographic atom probe. Roughly globular and some times elongated T' precipitates are present in the alloy aged at 140 d egrees C for 24 hours after solution heat treatment and water quenchin g, with a number density of 1.8 x 10(17) cm(-3). The volume fraction o f the phase is close to 4.5%. The T' precipitates were found to have a n average composition of 37.5 at% Mg, 36.5 at% Al and 26 at% Zn, which is, within experimental error, identical to that of the stable T phas e Mg-32(Al,Zn)(49).