DYNAMIC RECRYSTALLIZATION DURING HOT DEFORMATION OF Mg-Zn-Ca

Mechanical and chemical properties of magnesium and its alloys can be significantly improved by decreasing grain size which can be achieved by continuous or discontinuous dynamic recrystallization activated during hot deformation. The present work is focused on the study of the mechanism of dynamic recrystallization modifying the microstructure of Mg-4Zn and Mg-4Zn-0.4Ca alloys (in wt.%) during uniaxial compression at 240 degrees C with constant strain rate of 0.001 s(-1) and three different final strains of 0.09, 0.3 and close to 1. Light microscopic and scanning electron microscopic analyses of the microstructures showed that the grains were gradually fragmented with increasing strain. As a result inhomogeneous structure is generally formed and it is constituted of fine dynamically recrystallized grains of several micrometres and coarse unrecrystallized initial grains. Besides, the deformation condition led to deformation-induced precipitation. To elucidate the main mechanism of dynamic recrystallization contributing to the grain refinement, the electron backscatter diffraction analysis was used. Preliminary results showed that the evolution of the microstructure was favourably influenced by Ca addition that evoked the formation of the second phase particles.