An investigation was conducted to examine the mechanical behavior and microstructure evolution during deformation of ultrafine-grained pure magnesium at low temperatures within the temperature range of 296 -373 K. Discs were processed by high-pressure torsion until saturation in grain refinement. Dynamic hardness testing revealed a gradual increase in strain rate sensitivity up to m ≈ 0.2. High ductility was observed in the ultrafine-grained magnesium including an exceptional elongation of ~360% in tension at room temperature and stable deformation in micropillar compression. Grain coarsening and an increase in frequency of grain boundaries with misorientations in the range 15°  45° occurred during deformation in tension. The experimental evidence, when combined with an analysis of the deformation behavior, suggests that grain boundary sliding plays a key role in low strain rate deformation of pure magnesium when the grain sizes are at and below ~5 µm.

Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned (nt) columnar grains with high-density 9R phase in Al(Fe) solid solutions. The nt Al-Fe alloy coatings reach a maximum hardness of ≈5.5 GPa, one of the strongest binary Al alloys ever created. In situ uniaxial compressions show that the nt Al-Fe alloys populated with 9R phase have flow stress exceeding 1.5 GPa, comparable to high-strength steels. Molecular dynamics simulations reveal that high strength and hardening ability of Al-Fe alloys arise mainly from the high-density 9R phase and nanoscale grain sizes.

High Entropy alloys (HEAs) are solid solution alloys containing five or more principal elements in equal or near equal atomic percent (at %). We synthesized Al 0.7 CoCrF eN i HEA by vacuum arc melting and homogenized it at 1250 • C for 50 hours. The microstructure shows the presence of two phases: the Body-Centered Cubic (BCC: A2+B2) and the Face-Centered Cubic (FCC). Using the Focused Ion Beam, we fabricated single-crystalline cylindrical nano-pillars from each phase within individual grains in the Al 0.7 CoCrF eN i HEA. These nano-pillars had diameters ranging from 400 nm to 2 µm and were oriented in the [324] direction of the FCC phase and in the [001] direction of the BCC phase. Uniaxial compression experiments revealed that the yield strength is 2.2 GPa for the 400 nm diameter samples in the BCC phase and 1.2 GPa for the equivalent diameter samples in the FCC phase. We observed the presence of a size-effect in both phases, with smaller pillars having substantially greater strengths compared with bulk and with larger-sized samples. The size-effect power exponent for the BCC phase was-0.28, which is lower than that of most pure BCC metals, and the FCC phase had the exponent of-0.66, equivalent to most pure FCC metals. We discuss these results in the framework of nano-scale plasticity and the intrinsic lattice resistance through the interplay of the internal (microstructural) and external (dimensional) size effects.

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