Achieving extraordinary structural efficiency in a wrought magnesium rare earth alloy
TL;DR: The opportunities for wrought magnesium products in a wide range of structural and functional materials for transportation, energy generation, energy storage and propulsion are increasing due to th... as mentioned in this paper, which is the main reason for the increased interest in wrought magnesium.
Abstract: The opportunities for wrought magnesium products in a wide range of structural and functional materials for transportation, energy generation, energy storage and propulsion are increasing due to th...
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22 Apr 2021-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, compositional and micro-structural approaches that exhibit potential for a combination of shear induced phase transformation and twinning, thereby expanding beyond the slip based mechanisms are classified.
Abstract: The paradigm shift of alloying approach that led to high entropy alloys (HEAs) is now well established. Although the initial years were dominated by equiatomic approach, recent years have seen expansion in non-equiatomic compositional space that can be termed as complex concentrated alloys (CCAs). These HEAs/CCAs provide opportunities for tunable performance by manipulating deformation mechanisms. Understanding has advanced to the point that certain aspects of core effects (entropy of mixing, lattice distortion, sluggish diffusion, and cocktail effect) can be critically examined. In addition, new aspects of metastability engineering and emergence of a wide range of processing strategies has put this field on an exponential growth path. In this review, we categorize the compositional and microstructural approaches that exhibit potential for a combination of shear induced phase transformation and twinning, thereby expanding beyond the slip based mechanisms. The emerging HEAs give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), which have guided design of next-generation steels over the last 20 years to a new level. For TRIP HEAs, the ductility can be extended to as high as 50% while maintaining a strength exceeding 1 GPa. On the other hand, hierarchical microstructural engineering in AlxCoCrFeNi alloys can lead to over 2 GPa strength and >10% ductility. Observations of evolving c/a ratio in HCP phase of certain HEAs hint at possibility of new micromechanisms. While crack tip twin-bridging has been shown as a key mechanism to extend the toughness, concurrent phase transformation at the crack tip has been shown to push the fatigue endurance limit. Tunability of deformation mechanisms in HEAs is unprecedented as compared to the conventional metallic materials, particularly in compositions that exhibit shear induced transformation. The opportunities can be further enhanced by integrating the compositional and microstructure domains, and these aspects are highlighted in this review. The microstructural tailoring can take advantage of high enthalpy states in metastable HEAs with low stacking fault energy values of
15 citations
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TL;DR: In this article, a new strengthening mechanism involving the nano substructure with boundary segregation of Gd atoms, high density nano Gd clusters induced by dislocations, and high density dynamical precipitates has been found in Mg-Gd binary alloys.
Abstract: A high-strength binary Mg–15Gd alloy plate, prepared by the conventional extrusion, warm-rolling and aging, exhibits an excellent mechanical property with 504, 518 MPa and 4.5% for yield strength, ultimate tensile strength and elongation, which is mainly attributed to the nano substructure with boundary segregation of Gd atoms, the high-density nano clusters induced by dislocations in the interior of grains, the high-density dynamical precipitates with submicron size, and the strong basal texture. GRAPHICAL ABSTRACT IMPACT STATEMENT A new strengthening mechanism involving the nano substructure with Gd segregation, high-density nano Gd clusters induced by dislocations, and high-density dynamical precipitates has been found in Mg–Gd binary alloys.
15 citations
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TL;DR: In this paper , the effect of grain size and the type and amount of secondary phase particles on the superplasticity of Mg alloys was systematically examined and reviewed, and the critical conditions for achieving LTS, HSRS and simultaneous achievement of LTS and HSRS were calculated and proposed, and their importance was discussed.
Abstract: The tensile elongation behavior and deformation mechanisms of superplastic Mg alloys and Mg composites were examined by extensively reviewing the literature published from the time of the first report on the superplasticity of Mg alloys to the present day. Studies on the superplasticity of Mg alloys have been conducted mainly on Mg-Al-Zn (AZ) series alloys, Mg-Zn-Zr (ZK), Mg-Li and Mg-RE (rare earth) alloys, and in recent years, Mg-RE alloys have attracted the greatest attention. The effect of grain size and the type and amount of secondary phase particles on the superplasticity of Mg alloys was systematically examined and reviewed. The alloys processed by severe plastic deformation (SPD) and powder-metallurgy methods have smaller grain sizes and exhibit superior superplasticity compared to conventionally processed (by extrusion and rolling) Mg alloys. For the AZ alloys, as the volume fraction of the Mg 17 Al 12 phase increases, smaller grains are obtained, and the low-temperature superplasticity (LTS) and high-strain-rate superplasticity (HSRS) characteristics become enhanced. The ZK60 alloy with finely dispersed MgZn 2 particles exhibits excellent LTS, while the Mg-RE alloys with a high fraction of thermally stable particles exhibit excellent HSRS. Mg-Li alloys can exhibit LTS even at room temperature due to the presence of a high-volume fraction of the body centered cubic (BCC) phase where atomic diffusivity is high. Grain boundary diffusion- and lattice diffusion-controlled grain boundary sliding are found to operate as the dominant deformation mechanisms below ~ 473 K and above ~ 673 K, respectively, at small grain sizes. Deformation mechanism maps were constructed based on the analysis of the deformation behavior of superplastic Mg alloys, and from the maps, the critical conditions for achieving LTS, HSRS and simultaneous achievement of LTS and HRSR were calculated and proposed, and their importance was discussed.
14 citations
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TL;DR: In this article, the tensile yield strength (TYS) of Mg-13Gd alloy can reach 350 MPa by hot extrusion with an extrusion ratio of 4.
Abstract: Ultra-high strength is obtained in the simple binary Mg-Gd alloy with only a small extrusion ratio, and its main strengthening contribution is different from that reported in previous works. The tensile yield strength (TYS) of Mg-13Gd alloy can reach 350 MPa by hot extrusion with an extrusion ratio of 4. The strong texture and internal dislocation pinning of the un-dynamically recrystallized (un-DRXed) region with large proportion contribute greatly to the strength of as-extruded alloy. It is found for the first time that aging precipitation only occurs within the large un-DRXed grains but not in the fine DRXed grains. The TYS of extruded + peak-aged alloy increases to 470 MPa. The ultra-high strength is mainly related to texture strengthening and precipitation strengthening, rather than fine grain strengthening and precipitation strengthening in the conventional Mg alloys with large plastic deformation.
8 citations
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TL;DR: As the forging counterpart of fusion-based additive processes, additive friction stir deposition offers a solid-state deformation processing route to metal additive manufacturing, in which every vo... as discussed by the authors.
Abstract: As the forging counterpart of fusion-based additive processes, additive friction stir deposition offers a solid-state deformation processing route to metal additive manufacturing, in which every vo...
8 citations
References
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TL;DR: With a density of 1.74 g/cm3—about 30% less than aluminum, one-quarter that of steel, and nearly the same as many polymers—magnesium is attractive for lightweight structural systems and, most notably, automotive systems.
Abstract: The compelling need for lightweight, energy-efficient, environmentally benign engineering systems is driving the development of a wide range of structural and functional materials for energy generation, energy storage, propulsion, and transportation. These challenges motivate wider spread use of magnesium—the eighth most common element in the earth's crust and also extractable from seawater. In addition, the ease of recycling, compared with polymers, makes magnesium alloys environmentally attractive. Importantly, with a density of 1.74 g/cm3—about 30% less than aluminum, one-quarter that of steel, and nearly the same as many polymers—magnesium is attractive for lightweight structural systems and, most notably, automotive systems. A typical car weighing 1525 kg currently contains about 975 kg of steel, 127 kg of Al, 114 kg of polymeric materials, and 5 to 6 kg of magnesium ( 1 ). It is estimated that 22.5 kg of mass reduction would improve fuel efficiency by around 1%; thus, automotive manufacturers worldwide have goals to increase the Mg content of automobiles to between 45 and 160 kg ( 1 , 2 ).
615 citations
"Achieving extraordinary structural ..." refers background in this paper
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TL;DR: In this article, the authors present observations of low-temperature superplasticity in nanocrystalline nickel, 1420-Al, and Ni3Al, which is the lowest normalized super-plastic temperature reported for any crystalline material.
Abstract: Superplasticity — the ability of a material to sustain large plastic deformation — has been demonstrated in a number of metallic, intermetallic and ceramic systems. Conditions considered necessary for superplasticity1 are a stable fine-grained microstructure and a temperature higher than 0.5 T m (where T m is the melting point of the matrix). Superplastic behaviour is of industrial interest, as it forms the basis of a fabrication method that canbeused to produce components having complex shapes from materials that are hard to machine, such as metal matrix composites and intermetallics. Use of superplastic forming may become even more widespread if lower deformation temperatures can be attained. Here we present observations of low-temperature superplasticity in nanocrystalline nickel, a nanocrystalline aluminium alloy (1420-Al), and nanocrystalline nickel aluminide (Ni3Al). The nanocrystalline nickel was found to be superplastic ata temperature 470 °C below that previously attained2: this corresponds to 0.36T m, the lowest normalized superplastic temperature reported for any crystalline material. The nanocrystalline Ni3Al was found to be superplastic at a temperature 450 °C below the superplastic temperature in the microcrystalline regime3.
530 citations
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TL;DR: In this article, the evolution of the microstructure from as-cast to cast-T4 to castT6 involves solid solution+eutectic compound+supersaturated solid solution + cuboid-shaped compound.
Abstract: Microstructure and mechanical properties of Mg–10Gd–2Y–0.5Zr (wt.%) alloy in a series of tempers, including as-cast, cast-T4, cast-T6 and extruded-T5 conditions, have been investigated. The evolution of the microstructure from as-cast to cast-T4 to cast-T6 involves solid solution + eutectic compound → supersaturated solid solution + cuboid-shaped compound → solid solution + β′ precipitates + cuboid-shaped compound. Zirconium cores exist in all these conditions. Effective grain refinement is attained by hot extrusion with a small extrusion ratio (∼9.3). A good combination of high strength and sufficient ductility at room temperature is achieved for the cast-T6 alloy by optimizing the heat treatment parameters and for the extruded-T5 alloy extruded at 673 K, whose ultimate tensile strengths, tensile yield strengths and elongations are 362, 239 MPa and 4.7%, and 403, 311 MPa and 15.3%, respectively. Moreover, the strengths decrease gently from room temperature to 200 °C with a gradual increase of elongation. Existing traditional strengthening theories, together with data from microstructural characterization and mechanical properties are used to determine the magnitude of individual contribution. Strengthening due to precipitation is the largest contribution to alloy strength, either in cast-T6 condition or in extruded-T5 condition. The grain boundary strengthening also contributes significantly after hot extrusion.
517 citations
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TL;DR: In this article, an ingot metallurgy process with hot extrusion followed by aging has been used to produce an extraordinary high-strength Mg-1.8Gd−1.7Zn−0.2Zr alloy with ultimate tensile strength of 542 MPa, proof stress of 473 MPa and elongation to failure of 8.0%.
Abstract: Extraordinary high-strength Mg–1.8Gd–1.8Y–0.7Zn–0.2Zr alloy has successfully been fabricated by an ingot metallurgy process with hot extrusion followed by aging. The sample exhibits an ultimate tensile strength of 542 MPa, proof stress of 473 MPa and elongation to failure of 8.0%. These high strengths are achieved as a result of fine precipitates due to the aging and dynamic precipitation at the grain boundaries of dynamically recrystallized grains. These precipitates also substantially enhance the compressive proof stress, resulting in improvement in the yield anisotropy.
380 citations
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