Microstructure and damping behavior of pure magnesium in the grain size spectrum from micron to nanometer

Abstract

The damping mechanism of Mg alloys is commonly illustrated by the G-L theory, based on the configuration, movement, and interaction of dislocations in micron-scale metals. In this study, pure Mg bars were prepared with grain sizes from micron to nanometer scales, and the impacts exerted by grain size on the microstructure and the damping behavior were systematically studied. Results show that the dislocation density inside grains first increased with refining the grains, and then decreased when the grain size was less than 77 nm because a large fraction of dislocations were accommodated in grain boundaries. In samples with grain sizes 6 μm ∼131 nm, the damping property is dominated by the dislocation mechanism with close correlation to the intragranular dislocation density. However, once the grain size reaches below 77 nm, the damping performance is dominated by the grain boundary mechanism, which is significantly influenced from the grain boundary density. Thus, as the grain is refined, the strain amplitude independent damping capacity Q₀⁻¹ first increased, then decreased and increased again, that is, Q₀⁻¹ (6 μm) < Q₀⁻¹ (265 nm) < Q₀⁻¹ (131 nm) > Q₀⁻¹ (77 nm) < Q₀⁻¹ (60 nm) < Q₀⁻¹ (47 nm). Meanwhile, as the grain size decreased, the strain amplitude dependent damping capacity Q_h⁻¹ decreased first, then increased, that is, Q_h⁻¹ (6 μm) > Q_h⁻¹ (265 nm) > Q_h⁻¹ (131 nm) < Q_h⁻¹ (77 nm) < Q_h⁻¹ (60 nm) < Q_h⁻¹ (47 nm). This work offers a novel route for balancing the damping-mechanical performances of pure Mg.