GEOMETRIC DYNAMIC RECRYSTALLIZATION IN HOT TORSION OF AL-SMG-0.6MN (AA5083)

Geometric dynamic recrystallization (GDRX) is a process in which a ref ined and nearly equiaxed grain structure is formed, because grain boun daries which have become serrated during formation of subgrains in the course of hot deformation recombine as serrations pinch off or as the grains thin down. GDRX was first found in aluminium and more recently in Al-Mg solid solution. In the present work the question was address ed whether GDRX occurs also in an industrial Al alloy (5083) containin g particles, Specimens were deformed in torsion from 473 to 773 K at e quivalent (surface) strain rates between 10(-3) and 4 s(-1) to strains up to 3.6. Under these conditions the egg tray model predicts that GD RX win occur. This is indeed found from observations of the grain stru cture with light and electron microscopy. The results indicate that GD RX occurs not only by recombination of opposite boundaries of the thin ned grain but also by pinching off of serrations. The size of the GDRX grains is about two to three times the subgrain size. The close simil arity to Al-5Mg means that the particles in the alloy do not prevent t he small-scale grain boundary migration which is necessary to form the serrations. Static recrystallization after hot deformation destroys t he DRX structure, if the specimen is not cooled fast enough.