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Aluminum alloys are widely used because they are lightweight and exhibit high strength. In recent years, spark plasma sintering (SPS) technology has emerged as a viable approach to sinter materials due to its application of rapid heating and high pressure. In this study, SPS was chosen to consolidate dense ultrafine-grained (UFG) bulk samples using cryomilled nanostructured Al 5083 alloy (Al-4.5Mg-0.57Mn-0.25Fe, wt pct) powder. Both bimodal microstructure and banded structure were observed through transmission electron microscopy (TEM) investigation. The evolution of such microstructures can be attributed to the starting powder and the process conditions, which are associated with the thermal, electrical, and pressure fields present during SPS. A finite element method (FEM) was also applied to investigate distributions in temperature, current, and stress between metallic powder particles. The FEM results reveal that the localized heating, deformation, and thermal activation occurring at interparticle regions are associated with the formation of the special microstructure.