Mechanical Flow Response and Anisotropy of Ultra-fine Grained Magnesium and Zinc Alloys PDF Download
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Author: Majid H. Al Maharbi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Hexagonal closed packed (hcp) materials, in contrast to cubic materials, possess several processing challenges due to their anisotropic structural response, the wide variety of deformation textures they exhibit, and limited ductility at room temperature. The aim of this work is to investigate, both experimentally and theoretically, the effect os severe plastic deformation, ultrafine grain sizes, crystallographic textures and number of phases on the flow stress anisotropy and tension compression asymmetry, and the mechanisms responsible for these phenomena in two hcp materials: AZ31B Mg alloy consisting of one phase and Zn-8wt.% Al that has an hcp matrix with a secondary facecentered cubic (fcc) phase. Mg and its alloys have high specific strength that can potentially meet the high demand for light weight structural materials and low fuelconsumption in transportation. Zn-Al alloys, on the other hand, can be potential substitutes for several ferrous and non-ferrous materials because of their good mechanical and tribological properties. Both alloys have been successfully processed using equal channel angular extrusion (ECAE) following different processing routes in order to produce samples with a wide variety of microstructures and crystallographic textures for revealing the relationship between microstructural parameters, crystallographic texture and resulting flow stress anisotropy at room temperature. For AZ31B Mg alloy, the texture evolution during ECAE following conventional and hybrid ECAE routes was successfully predicted using visco-plastic self-consistent (VPSC) crystal plasticity model. The flow stress anisotropy and tension-compression (T/C) asymmetry of the as received and processed samples at room temperature were measured and predicted using the same VPSC model coupled with a dislocation-based hardening scheme. The governing mechanisms behind these phenomena are revealed as functions of grains size and crystallographic texture. It was found that the variation in flow stress anisotropy and T/C asymmetry among samples can be explained based on the texture that is generated after each processing path. Therefore, it is possible to control the flow anisotropy and T/C asymmetry in this alloy and similar Mg alloys by controlling the processing route and number of passes, and the selection of processing conditions can be optimized using VPSC simulations. In Zn-8wt.% Al alloy, the hard phase size, morphology, and distribution were found to control the anisotropy in the flow strength and elongation to failure of the ECAE processed samples.
Author: Majid H. Al Maharbi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Hexagonal closed packed (hcp) materials, in contrast to cubic materials, possess several processing challenges due to their anisotropic structural response, the wide variety of deformation textures they exhibit, and limited ductility at room temperature. The aim of this work is to investigate, both experimentally and theoretically, the effect os severe plastic deformation, ultrafine grain sizes, crystallographic textures and number of phases on the flow stress anisotropy and tension compression asymmetry, and the mechanisms responsible for these phenomena in two hcp materials: AZ31B Mg alloy consisting of one phase and Zn-8wt.% Al that has an hcp matrix with a secondary facecentered cubic (fcc) phase. Mg and its alloys have high specific strength that can potentially meet the high demand for light weight structural materials and low fuelconsumption in transportation. Zn-Al alloys, on the other hand, can be potential substitutes for several ferrous and non-ferrous materials because of their good mechanical and tribological properties. Both alloys have been successfully processed using equal channel angular extrusion (ECAE) following different processing routes in order to produce samples with a wide variety of microstructures and crystallographic textures for revealing the relationship between microstructural parameters, crystallographic texture and resulting flow stress anisotropy at room temperature. For AZ31B Mg alloy, the texture evolution during ECAE following conventional and hybrid ECAE routes was successfully predicted using visco-plastic self-consistent (VPSC) crystal plasticity model. The flow stress anisotropy and tension-compression (T/C) asymmetry of the as received and processed samples at room temperature were measured and predicted using the same VPSC model coupled with a dislocation-based hardening scheme. The governing mechanisms behind these phenomena are revealed as functions of grains size and crystallographic texture. It was found that the variation in flow stress anisotropy and T/C asymmetry among samples can be explained based on the texture that is generated after each processing path. Therefore, it is possible to control the flow anisotropy and T/C asymmetry in this alloy and similar Mg alloys by controlling the processing route and number of passes, and the selection of processing conditions can be optimized using VPSC simulations. In Zn-8wt.% Al alloy, the hard phase size, morphology, and distribution were found to control the anisotropy in the flow strength and elongation to failure of the ECAE processed samples.
Author: Sonia Modarres Razavi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Magnesium and its alloys have been considered as alternatives to aluminum alloys and steels for structural applications in automotive and aerospace applications due to their superior specific strength and light-weight. However, they have hexagonal-close packed (hcp) structure, and thus have a small number of deformation systems resulting in low ductility and formability near room temperature, anisotropic thermo-mechanical response and strong deformation textures. The aim of this work is to investigate experimentally the effect of crystallographic texture generated during severe plastic deformation (SPD), on the subsequent formability and mechanical flow anisotropy in AZ31B Mg alloy. The proper control of grain size and texture through SPD is expected to result in better low temperature formability and better control of mechanical flow anisotropy. AZ31B Mg alloy has been successfully processed using equal channel angular extrusion (ECAE) following different processing routes, multiple passes, and different processing temperatures, in order to obtain samples with a wide variety of grain sizes, ranging from ~370 nm up to few microns, and crystallographic textures. Low temperature processing of the AZ31B Mg alloy was successful after initial high temperature processing. Smaller grain sizes were achieved using the temperature step-down method leading to incremental reduction in grain size at each ECAE pass. The temperature step-down method was utilized to develop hybrid ECAE routes to obtain specific crystallographic textures. Optimized hybrid ECAE routes were developed which resulted in a high strength/high ductility material with the average grain size of ~370 nm. The ECAE processed alloy showed a high tensile yield strength of ~380 MPa that has never been reported so far in AZ31 ingot metallurgy Mg alloys. The influence of grain size on the critical stress for the activation of individual deformation mechanisms was also investigated by systematically controlling the texture and grain size, and assuming the activation of mainly a single deformation mechanism through the careful selection of the loading direction on the processed samples. It was revealed that the Hall-Petch slope for the basal slip was much smaller than those of prismatic slip and tensile twinning.
Author: Dalong Zhang
Publisher:
ISBN: 9781369201123
Category :
Languages : en
Pages :
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Book Description
Mg and its alloys are promising candidates for light-weight structural applications, e.g., aircraft, automobile, electronic, etc. However, the inherent hexagonal close packed crystal structure makes the deformation of Mg anisotropic, namely deformation only occurs predominantly by dislocation slip in the close-packed (0001) plane (i.e., basal plane), or by deformation twinning in {101̄2} planes. Both basal slip and twinning cause the crystal to re-orient. Consequently, polycrystalline Mg alloys that have undergone thermomechanical processing usually contain strong texture, i.e., preferred crystallographic orientation in grains. The texture in turn leads to anisotropic deformation in wrought Mg alloys. For example, in extruded Mg alloys, the compressive yield strength is usually much lower than the tensile yield strength (so-called yield asymmetry and strength differential). It is the anisotropy that hinders the broader application of Mg alloys. Recent modeling studies on Mg predict that certain alloying elements, particularly rare-earth elements (e.g., Y, Ce, Nd, Gd, etc.), could alter the active deformation modes and enhance homogeneous deformation and overall mechanical properties in Mg. Therefore, the objective of this dissertation research is to investigate experimentally the effects of alloying element Y in reducing the intrinsic and extrinsic anisotropy, modifying texture, and enhancing the overall strength and ductility for Mg. In addition, the research also uncovered some unexpected "side effects" of Y and these phenomena were studied and explained from a fundamental perspective. The methodology used in this work is described as follows. Ultrafine grained Mg 2.5 at.% Y alloy (UFG Mg-2.5Y) was prepared by powder metallurgy method, including gas atomization for producing Mg-2.5Y powder, degassing and hot isostatic pressing (HIP), and hot extrusion. Both the as-HIPed and the as-extruded materials were characterized by electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM), and/or atom probe tomography (APT). It is noted that different configurations of stacking faults (all in basal plane, i.e., basal stacking faults, BSFs for short) were observed in the as-extruded Mg-2.5Y, whereas no BSFs were documented in the as-HIPed alloy. Feasible models to explain the formation of BSFs were proposed based on the activity of different dislocations. Tension and compression tests were carried out along the extrusion direction (ED) for UFG Mg-2.5Y. Unlike common Mg alloys exhibiting yield asymmetry, the UFG Mg-2.5Y exhibits yield "symmetry" and significantly reduced strength differential. Namely, the deformation is more isotropic. In addition to post-mortem TEM characterization for deformed UFG Mg-2.5Y, in-situ TEM was also performed, in an effort to understand the fundamental deformation mechanisms in UFG Mg-Y that lead to reduced anisotropy. In-situ TEM for single-crystal Mg-Y nano-pillars reveals that deformation twinning is replaced by dislocation slip in non-basal planes (i.e., prismatic planes), which diametrically differs from any other Mg alloys. However, it is noted that deformation twinning still occurs in the polycrystalline UFG Mg-2.5Y occasionally, and a new type of stacking faults (i.e., prismatic stacking faults, PSFs for short) may be present in the vicinity of twins. Feasible mechanisms explaining the formation of PSFs are proposed.
Author: Saadi Habib
Publisher:
ISBN:
Category :
Languages : en
Pages : 352
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Book Description
Magnesium alloys have been at the forefront as possible alternatives to conventional materials such as aluminum and steel for their high specific-strength. However, magnesium alloys exhibit anisotropy, tension-compression asymmetry, and quasi-brittle fracture at ambient temperature, which is exacerbated at high strain rates. It is well known that alloying with rare-earth elements can improve the low uniaxial ductility in comparison with conventional magnesium alloys. Therefore, the mechanical response and texture evolution of a rare-earth-containing magnesium alloy sheet, ZEK100, are investigated under different loading conditions to characterize the anisotropy, tension-compression asymmetry, strain rate sensitivity and thermomechanical response. A reduced-order crystal plasticity model that defines extension twinning, basal a slip, and non-basal slip as the deformation mechanisms, is used to model the experimental results and to give an insight in the active deformation mechanism. In addition, the fracture behavior of ZEK100 is also investigated at different stress states and strain rates. A variety of sample geometries loaded along different processing directions are used to achieve different stress states and deformation mechanisms. Surface strain maps for all the specimens are measured using the digital image correlation (DIC) technique to quantify the strain at fracture. ZEK100 exhibits larger strain at fracture across the gage section of the test specimens aligned with the transverse direction (TD) than specimens aligned with the rolling direction (RD); however, the opposite is shown for the local strain measurements at fracture. Therefore, the crystal plasticity model is used to simulate each loading condition to understand the anisotropic ductile fracture behavior of ZEK100. Using the stress states and deformation mechanisms from the simulations, a novel anisotropic criterion is developed which is an extension of the Hosford-Coulomb (HC) fracture model. The new anisotropic criterion accounts for the role of different deformation mechanisms on the anisotropic fracture response of ZEK100.
Author: Taku Sakai
Publisher:
ISBN: 9789533075204
Category :
Languages : en
Pages :
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Author: United States. National Bureau of Standards
Publisher:
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Category : Zinc
Languages : en
Pages : 246
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Author: Alan Luo
Publisher: Springer Nature
ISBN: 3030724328
Category : Technology & Engineering
Languages : en
Pages : 272
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Book Description
This collection from the 12th International Conference on Magnesium Alloys and Their Applications (Mg 2021)—the longest running conference dedicated to the development of magnesium alloys—covers the breadth of magnesium research and development, from primary production to applications to end-of-life management. Authors from academia, government, and industry discuss new developments in magnesium alloys and share valuable insights. Topics in this volume include but are not limited to the following: Primary production Alloy development Solidification and casting processes Forming and thermo-mechanical processing Other manufacturing process development (including joining and additive manufacturing) Corrosion and protection Modeling and simulation Structural, functional, biomedical, and energy applications Advanced characterization and fundamental theories Recycling and environmental issues
Author: Qi Yang
Publisher:
ISBN: 9780542366987
Category :
Languages : en
Pages :
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Author:
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ISBN:
Category : Chemistry
Languages : en
Pages : 2566
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Author:
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ISBN:
Category : Metallurgy
Languages : en
Pages : 1076
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