Weight Loss with Magnesium Alloys

Pollock, Tresa M.

doi:10.1126/science.1182848

Cited by 974 publications

(281 citation statements)

References 17 publications

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“…Equation (2) thus gives directly the core energy difference. For edge dislocations, the core energy difference can be estimated at r → r c or by subtracting the computed elastic energy from equation (1). In calculations of the GSF energy, periodic boundary conditions are used in the x and z directions while the y surfaces are free with height larger than 100 times the interplanar spacing along y.…”

Section: Simulation Methods and Geometriesmentioning

confidence: 99%

Magnesium interatomic potential for simulating plasticity and fracture phenomena

Francis

Curtin

2014

Modelling Simul. Mater. Sci. Eng.

138

104

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Abstract.Magnesium has multiple dislocation and twinning systems with starkly different properties, which make its plastic deformation strongly anisotropic and highly complex. Existing empirical interatomic potentials fail to capture the full scope of these properties, making current molecular statics and dynamics simulation results of limited quantitative and predictive use. Here, based on the work by Kim et al, a new modified embedded-atom method potential for magnesium is introduced and rigorously validated against existing ab initio, continuum theory and experimental results. The new potential satisfactorily reproduces all the necessary mechanical properties for plastic deformation, including the various generalized stacking fault energy surfaces, dislocations core structures, Peierls stresses, surface energies, and basal plane cohesive strength. The capability of this potential to accurately describe all the important slip systems and fracture behavior makes it valuable for future realistic atomistic studies of general magnesium deformation and failure problems.

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Section: Simulation Methods and Geometriesmentioning

confidence: 99%

Magnesium interatomic potential for simulating plasticity and fracture phenomena

Francis

Curtin

2014

Modelling Simul. Mater. Sci. Eng.

138

104

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“…Magnesium (Mg) is the ultimate lightweight metal, with a density 23% that of steel and 66% that of aluminum, and so has tremendous potential to achieve energy efficiency 4 . In spite of this tantalizing property, Mg generally exhibits low ductility, insufficient for the forming and performance of structural components.…”

Section: Introductionmentioning

confidence: 99%

The origins of high hardening and low ductility in magnesium

Curtin

2015

Nature

568

170

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Magnesium is the ultimate lightweight structural metal but exhibits low ductility connected to unusual, mechanistically-unexplained, dislocation/plasticity phenomena, which make it difficult to form and use in energy-saving lightweight structures. Here, long-time molecular dynamics simulations using a DFT-validated interatomic potential reveal the fundamental origins of the previouslyunexplained phenomena and show a clear path toward design of new ductile magnesium alloys. The key c + a dislocation is metastable on easy-glide pyramidal II planes and undergoes a thermallyactivated, stress-dependent transition to one of three lower-energy, basal-dissociated immobile dislocation structures, which (i) cannot contribute to plastic straining and (ii) serve as strong obstacles to the motion of all other dislocations. The transition is intrinsic to magnesium, driven by reduction in dislocation energy and predicted to occur at very high frequency at room temperature, thus eliminating all major dislocation slip systems able to contribute to c-axis strain and leading to its low ductility.Enhancing ductility can thus be achieved by delaying, in time and temperature, the transition from the easy-glide metastable dislocation to the immobile basal-dissociated structures, and our results provide the underlying insights needed to guide the design of ductile magnesium alloys. * Corresponding author: william.curtin@epfl.ch 1 This is a post-print of the following article: Wu, Z. & Curtin, W. A. The origins of high hardening and low ductility in magnesium. Nature 526, 62-67 (2015). The final publication is available at http://dx.doi.org/10.1038/nature15364Developing lightweight structural metal is a crucial step on the path toward reduced energy consumption in many industries, especially automotive 1,2 and aerospace 3 . Magnesium (Mg) is the ultimate lightweight metal, with a density 23% that of steel and 66% that of aluminum, and so has tremendous potential to achieve energy efficiency 4 . In spite of this tantalizing property, Mg generally exhibits low ductility, insufficient for the forming and performance of structural components. The low ductility is associated with the inability of hexagonally-close-packed (hcp) Mg to deform plastically in the crystallographic c direction, which is accomplished primarily by dislocation glide on the pyramidal II plane with the c + a Burgers vector 5 (see Fig. 1).Experiments reveal a range of unusual, confounding, conflicting, and mechanistically-unexplained phenomena connected to c+a dislocations that coincide with the inability of Mg to achieve high plastic strains 6 . Uncovering and controlling the fundamental behavior of c + a dislocations is thus the key issue in Mg, and any solution would catapult Mg science, technology, and applications forward. Success would enable, for instance, lightweight automobiles that would consume less energy, independent of the energy source, and thus act as a multiplier for many other energyreduction strategies.Due to its critical importance and pro...

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“…Moreover, Mg-alloys have excellent recyclability and are ideal for transportation applications providing enormous potential for energy savings [1][2][3][4][5][6][7]. However, magnesium has certain limitations when compared with other metallic systems and polymers [6]. Since magnesium has a hexagonal close packed (hcp) structure, it has a limited number of active slip systems at room temperature [8,9] which leads to failure in polycrystalline Mg-alloys at ambient conditions before dislocation glide can occur [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

“…Among structural materials, Magnesium (Mg) has the highest strength-to-weight ratio. Moreover, Mg-alloys have excellent recyclability and are ideal for transportation applications providing enormous potential for energy savings [1][2][3][4][5][6][7]. However, magnesium has certain limitations when compared with other metallic systems and polymers [6].…”

Section: Introductionmentioning

confidence: 99%

“…Since magnesium has a hexagonal close packed (hcp) structure, it has a limited number of active slip systems at room temperature [8,9] which leads to failure in polycrystalline Mg-alloys at ambient conditions before dislocation glide can occur [10][11][12]. In an effort to overcome these low strength shortcomings, recent studies have considered the effects of adding certain alloying elements to magnesium, such as Al-Zn, Al-Si, Al-Ca, Al-Sr, Sn-Ca, Zr-Y, and minute traces of other rare-earth (RE) elements [6,[13][14][15][16][17][18][19][20][21][22][23]. The objective of all these studies has been to qualitatively identify the principles governing solute and precipitate strengthening and ductility while improving manufacturability, as well as lowering production costs of the alloys (e.g., [17,24]).…”

Section: Introductionmentioning

confidence: 99%

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Atomic-scale investigation of creep behavior in nanocrystalline Mg and Mg–Y alloys

2015

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Magnesium (Mg) and its alloys offer great potential for reducing vehicular mass and energy consumption due to their inherently low densities. Historically, widespread applicability has been limited by low strength properties compared to other structural Al-, Ti-and Fe-based alloys. However, recent studies have demonstrated high-specific-strength in a number of nanocrystalline Mg-alloys. Even so, applications of these alloys would be restricted to low-temperature automotive components due to microstructural instability under high temperature creep loading. Hence, this work aims to gain a better understanding of creep and associated deformation behavior of columnar nanocrystalline Mg and Mg-yttrium (Y) (up to 3at.%Y(10wt.%Y)) with a grain size of 5 nm and 10 nm. Using molecular dynamics (MD) simulations, nanocrystalline magnesium with and without local concentrations of yttrium is subjected to constant-stress loading ranging from 0 to 500 MPa at different initial temperatures ranging from 473 to 723 K. In pure Mg, the analyses of the diffusion coefficient and energy barrier reveal that at lower temperatures (i.e., T < ~423K) the contribution of grain boundary diffusion to the overall creep deformation is stronger that the contribution of lattice diffusion. However, at higher temperatures (T > ~423K) lattice diffusion dominates the overall creep behavior. Interestingly, for the first time, we have shown that the(101 ̅ 1), (101 ̅ 2),(101 ̅ 3) and (101 ̅ 6) boundary sliding energy is reduced with the addition of yttrium. This softening effect in the presence of yttrium suggests that the experimentally observed high temperature beneficial effects of yttrium addition is likely to be attributed to some combination of other reported creep strengthening mechanisms or phenomena such as formation of stable yttrium oxides at grain boundaries or increased forest dislocation-based hardening.

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Weight Loss with Magnesium Alloys

Abstract: New design and processing approaches for magnesium-based alloys are offering a variety of opportunities in lightweight and energy-efficient applications.

Cited by 974 publications

References 17 publications

Magnesium interatomic potential for simulating plasticity and fracture phenomena

Magnesium interatomic potential for simulating plasticity and fracture phenomena

The origins of high hardening and low ductility in magnesium

Atomic-scale investigation of creep behavior in nanocrystalline Mg and Mg–Y alloys

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