Principles of grain refinement in magnesium alloys processed by equal-channel angular pressing

Excerpt

Processing through the application of severe plastic deformation (SPD) provides a useful tool for introducing very significant grain refinement in bulk solids [1]. Although several SPD techniques are now available, processing by equal-channel angular pressing (ECAP) is especially attractive because it is easily scaled-up for use with large samples [2]. Numerous experiments have shown that processing by ECAP produces ultrafine-grain structures in a range of fcc metals, including Al and Cu, and this led to the development of a model for grain refinement based on the formation of an elongated array of subgrains or cells in the first pass of ECAP, the further development of elongated arrays in subsequent passes and the evolution of this structure into an array of equiaxed grains separated by high-angle grain boundaries [3]. In practice, there is excellent agreement between this model of grain refinement for fcc metals [3], the shearing patterns predicted in ECAP processing [4] and experimental observations of the microstructural evolution in Al single crystals [5, 6] and polycrystalline Al [7, 8] processed by ECAP. …