David Witkin

Al-Mg alloy engineered with bimodal grain size for high strength and increased ductility

Al–7.5Mg powders were cryomilled, then consolidated and extruded to produce bulk nanostructured material. The extrusions had a tensile yield strength of 641 MPa and an ultimate strength of 847 MPa. Additional samples were prepared by combining cryomilled powder unmilled Al–7.5Mg, resulting in extrusions with high strength and increased ductility.

Mechanical behavior of ultrafine-grained cryomilled Al 5083 at elevated temperature

The mechanical behavior of cryomilled and consolidated Al 5083 with a duplex ultrafine-grained microstructure is described for compression testing at different temperatures and strain rates. The relationship among flow stress, strain rate, and testing temperature provides an initial hotworking guide for finegrained cryomilled aluminum alloys. The ultrafine-grained material exhibits similar deformation characteristics, such as strain-rate sensitivity, which would be expected in a conventional aluminum alloy. These findings are discussed in the context of recent empirical and theoretical models for the deformation of materials with grain sizes between 100 and 1000 nm.

Bimodal Microstructure and Mechanical Properties of Cryomilled Nanocrystalline Al-7.5Mg

Abstract : The microstructure and mechanical properties consisting of tensile behavior and hardness of bulk nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders and then nanocrystalline powders blended with 15% and 30% coarse-grained Al-7.5Mg powders were consolidated by hot isostatic pressing (HIP) followed by extrusion to produce bulk nanocrystalline Al-7.5Mg alloys. Bimodal structures which enhance ductility and toughness of nanocrystalline metals were produced that consisted of nanocrystalline grains and elongated coarse-grain bands Examination of indentation revealed unusual deformation mechanisms and interactions between the coarse-grain bands and nanocrystalline regions. The ductile coarse-grain bands underwent extensive plastic deformation near indentation while nanocrystalline regions exhibited limited deformation.