Bimodal microstructure and deformation of cryomilled bulk nanocrystalline Al–7.5Mg alloy

The microstructure, mechanical properties and deformation response of bimodal structured nanocrystalline Al–7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al–7.5Mg powders, and then cryomilled nanocrystalline powders blended with 15 and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk nanocrystalline alloys. Bimodal bulk nanocrystalline Al–7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions, show balanced mechanical properties of enhanced yield and ultimate strength and reasonable ductility and toughness compared to comparable conventional alloys and nanocrystalline metals. The investigation of tensile and hardness test suggests unusual deformation mechanisms and interactions between ductile coarse-grain bands and nanocrystalline regions.