The nature of grain refinement in equal-channel angular pressing: a comparison of fcc and hcp metals

Equal-channel angular pressing is an effective tool for producing exceptional grain refinement in bulk polycrystalline metals. Typically, processing in this way refines the grains to the submicrometer level in a wide range of metals but recent experiments have established that the mechanism of grain refinement is different in fcc and hcp metals. Specifically, the refining of grains in aluminum involves the introduction of elongated bands of cells or subgrains and the subsequent evolution of this structure into an array of ultrafine grains whereas in magnesium the limited number of slip systems leads to the formation of new grains along the existing grain boundaries. Because of these limitations, magnesium alloys are especially susceptible to the production of materials having bimodal grain distribution