Dynamic recrystallization in pure magnesium

Microstructural evolution of commercial grade pure magnesium was studied du ring plastic deformation by torsion under high pressure at ambient temperat ure and by compression at temperatures ranging from 293 to 773 K and at a s train rate of 3 x 10(-3) s(-1). Grain refinement takes place by operation o f dynamic recrystallization (DRX) at all examined temperatures. The mechani sms of DRX change with temperature and strain. As a result, unusual depende ncies 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, whic h 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 (C DRX) yielding a steady-state flow operates frequently at temperatures rangi ng from 523 to 773 K. CDRX occurs mainly in overall recrystallization proce ss at elevated temperatures. Discontinuous DRX (DDRX) takes place by bulgin g of boundaries of coarse recrystallized grains evolved from twins it T = 7 23 K. DDRX occurs repetitively, but gives an insignificant contribution int o total recrystallization process. The present results suggest that the mec hanisms of DRX and the deformation mechanisms are closely related.