Abstract
Aluminum alloys with nanocrystalline (NC) and ultra-fine grain (UFG) size are of interest because of their high strength-typically more than 30% stronger than conventionally processed alloys. By generating NC powders via cryomilling in liquid nitrogen, a thermally stable UFG microstructure evolves during thermomechanical processing (TMP). The constituents that stabilize the microstructure-dispersed oxides and nitrides-also contribute to the strength of the system. By examining microstructures and stress-strain data generated for cryomilled pure Al and Al-Mg alloys, with various milling times and media, the strengthening mechanisms can be dissected to improve understanding of cryomilled Al alloys. Hall-Petch, Orowan, solid solution and dislocation hardening mechanisms are quantified based on experimentally developed UFG Al alloys crossing multiple investigations. Additionally, the intentional addition of ceramic particulates, such as Al(2)O(3) and B(4)C, provides the basis for analyzing systems using basic composite models.