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Dilute Mg alloys based upon earth-abundant elements, e.g., Al, Ca, and Zn have attractive combinations of strength, ductility, and workability. Even higher strength can be obtained in work-hardened material without the heat treatments required to induce Guinier-Preston zone strengthening of previously studied versions of these alloys. This stems from a slightly stronger crystallographic texture than is present after solutionizing, a high dislocation density, and to a lesser degree, a fine distribution of globular Zn-rich precipitates. The anisotropic plastic response of sheet material is described using an elasto-viscoplastic self-consistent (EVPSC) polycrystal model. Strain partitioning between grains during rolling-induced strain hardening is held responsible for the yield strength, ductility, and especially, strain hardening anisotropy. Texture-induced plastic anisotropy is well- known, but the effect of strong partitioning of strain between variously oriented grains is critical to explain what may be classified as a sort of strain path change (generalized Bauschinger) effect.
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Rare-earth- and aluminum-free, high strength dilute magnesium alloy for Biomedical Applications
Abstract Lightweight, recyclable, and plentiful Mg alloys are receiving increased attention due to an exceptional combination of strength and ductility not possible from pure Mg. Yet, due to their alloying elements, such as rare-earths or aluminum, they are either not economical or biocompatible. Here we present a new rare-earth and aluminum-free magnesium-based alloy, with trace amounts of Zn, Ca, and Mn (≈ 2% by wt.). We show that the dilute alloy exhibits outstanding high strength and high ductility compared to other dilute Mg alloys. By direct comparison with annealed material of the same chemistry and using transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and atom probe tomography analyses, we show that the high strength can be attributed to a number of very fine, Zn/Ca-containing nanoscale precipitates, along with ultra-fine grains. These findings show that forming a hierarchy of nanometer precipitates from just miniscule amounts of solute can invoke simultaneous high strength and ductility, producing an affordable, biocompatible Mg alloy.
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- PAR ID:
- 10293177
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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To obtain thorough understandings of precipitation process in heat-treatable Mg-Ca-Zn alloy, we revisited the precipitation process of a Mg-0.3Ca-0.6 Zn (at.%) dilute alloy during isothermal aging at 200 °C using an aberration-corrected scanning transmission electron microscope, atom probe tomography, and first-principles calculations. The monolayer G.P. zones form on the (0002)α plane in the peak-aged condition and transform into tri-atomic layer η'' and η' plates with a thickness of a single unit-cell height. The η' plates, then, form in pairs and stacks with energetically favorable 4–5 atomic layers of pure magnesium between the plates. While such a transformation path is similar to that seen in Mg-RE-Zn alloys (RE: rare-earth elements), the unique structure of coarse η1 plates that precipitate after the η' plates leads to a different precipitate microstructure evolution from the Mg-RE-Zn system. The η1 phase (Mg7Ca2Zn3) is unevenly distributed in the matrix after 100 h of aging and finally evolves to the equilibrium η phase (Mg10Ca3Zn6) phase with a hexagonal structure. First-principles calculations of energetics were performed to further identify the crystal structure and stability of the precipitates, supporting the following new precipitation sequence: S.S.S.S. → G.P. zones → η'' → η' → η' pairs and stacks / η1 → ηmore » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41598-020-72374-z
