Geometric dynamic recrystallization in hot torsion of Al5Mg0.6Mn (AA5083)

Geometric dynamic recrystallization (GDRX) is a process in which a refined and nearly equiaxed grain structure is formed, because grain boundaries 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 addressed whether GDRX occurs also in an industrial Al alloy (5083) containing particles. Specimens were deformed in torsion from 473 to 773 K at equivalent (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 GDRX will occur. This is indeed found from observations of the grain structure with light and electron microscopy. The results indicate that GDRX occurs not only by recombination of opposite boundaries of the thinned 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 similarity to Al5Mg means that the particles in the alloy do not prevent the small-scale grain boundary migration which is necessary to form the serrations. Static recrystallization after hot deformation destroys the DRX structure, if the specimen is not cooled fast enough.