Dynamic Recrystallization in Pure Magnesium

Microstructural evolution of commercial grade pure magnesium was studied during plastic deformation by torsion under high pressure at ambient temperature and by compression at temperatures ranging from 293 to 773 K and at a strain rate of 3×10−3 s−1. Grain refinement takes place by operation of dynamic recrystallization (DRX) at all examined temperatures. The mechanisms of DRX change with temperature and strain. As a result, unusual dependencies of recrystallized grain size against strain and recrystallized volume fraction against temperature are observed. In the temperature interval of 293–623 K the deformation twinning results in “twin” mechanism of DRX, which processes strain softening at an initial stage of deformation. At T≤423 K the other mechanism of low temperature DRX takes place at high strains. Such DRX is accompanied by strain hardening. In contrast, continuous DRX (CDRX) yielding a steady-state flow operates frequently at temperatures ranging from 523 to 773 K . CDRX occurs mainly in overall recrystallization process at elevated temperatures. Discontinuous DRX (DDRX) takes place by bulging of boundaries of coarse recrystallized grains evolved from twins at T=723 K . DDRX occurs repetitively, but gives an insignificant contribution into total recrystallization process. The present results suggest that the mechanisms of DRX and the deformation mechanisms are closely related.