Grain refinement in as-cast AZ80 Mg alloy under large strain deformation

Grain refinement in as-cast AZ80 magnesium alloy under large strain deformation was studied by hot multiple forging (MF). The results show that during the deformation there exists a critical strain controlling the degree of the homogeneity, which is in the range of 2–2.4. A homogeneous microstructure with fine dynamic recrystallized grains can be attained when the applied strain exceeds the critical strain and after that, it is difficult to get more grain refinement further. A main characteristic of microstructure evolution is directly associated with grain splitting due to the formation of microbands that develop in various directions. Such microbands intersect each other during hot MF, resulting in continuous subdivision of coarse grains into misoriented fine domains. Further deformation leads to increase in the number and misorientation of these boundaries and finally almost full development of fine equiaxed grains in high strain. New grains are concluded to be evolved by a kind of continuous reaction, that is essentially similar to continuous dynamic recrystallization.