Microband/twin recrystallization during back extrusion of AZ31 magnesium

The occurrence of dynamic recrystallization of microband and twins during severe plastic deformation of an AZ31 magnesium alloy was studied through optical and scanning electron microcopy as well as electron back scatter diffraction analyses. Microstructural observations indicated that the wavy boundaries of the microbands had diffused out and generated new boundaries within parent bands. Also the grains formed through twin fragmentation mechanism tend to acquire random orientations. Moreover, transverse boundaries segmented the twins into regions of ultra-fine and nano-scale size. A new so-called “twin-assisted” grain refinement mechanism was also recognized which adopted the orientations different from those produced by conventional recrystallization mechanisms. The latter mechanism is useful to assist texture weakening during thermomechanical processes of magnesium alloys.