Mechanical Behavior and the Role of Deformation Twinning in Wrought Magnesium Alloys Investigated Using Neutron and Synchrotron X-ray Diffraction PDF Download
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Author: Liang Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 231
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Book Description
The mechanical behaviors and the associated deformation mechanisms with a focus on extension twinning under monotonic and cyclic loadings are investigated using neutron and synchrotron diffractions in the wrought magnesium alloys, ZK60A and AZ31B. It has been demonstrated that the extension twinning plays significant roles in the mechanical behaviors. The significant tension-compression asymmetries and high anisotropies are observed. The tension-compression asymmetries are related to the twinning activation in one direction but not in the opposite direction. The high anisotropies are correlated with the initial texture distinction relative to the loading directions. The similar yielding stresses are noted irrespective of the strain direction and strain sign if the deformation is dominated by twinning, while they are usually different with respect to the loading conditions if the dislocation slip is dominant. The extension twinning under tension exhibits a similar behavior to that under compression, presumably due to the same Schmid stress introduced on the twinning plane along the twinning shear direction. However, the distribution of basal poles within the twins under tension is closely related to the initial texture, while they are always aligned with the compressive axis under compression. The low-cycle fatigue resistances follow the empirical Basquin and Coffin-Manson relationships with the texture dependency observed, related to the different activation sequences of twinning and detwinning involved, respectively, under tension and compression determined by the initial texture. Specifically, the post-detwinning deformation characteristics may be an important factor in understanding the texture dependency. The extension twinning is readily activated if an applied stress/strain supports c-axis extension of the hexagonal-close-packed (hcp) structure. The unique reorientation of the twins facilitates detwinning in the twinned areas during the subsequent strain/stress reversal. Therefore, the cyclic plastic deformation is dominated by the alternating twinning and detwinning, and the initial texture is recovered once detwinning capability is exhausted, concurrent with the disappearance of twin bands. In particular, detwinning occurs almost immediately in the twinned grains upon unloading, which is driven by the local tensile stress along their c-axes as a result of the stress redistribution between the soft- and hard-grain orientations due to the plastic anisotropy.
Author: Liang Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 231
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Book Description
The mechanical behaviors and the associated deformation mechanisms with a focus on extension twinning under monotonic and cyclic loadings are investigated using neutron and synchrotron diffractions in the wrought magnesium alloys, ZK60A and AZ31B. It has been demonstrated that the extension twinning plays significant roles in the mechanical behaviors. The significant tension-compression asymmetries and high anisotropies are observed. The tension-compression asymmetries are related to the twinning activation in one direction but not in the opposite direction. The high anisotropies are correlated with the initial texture distinction relative to the loading directions. The similar yielding stresses are noted irrespective of the strain direction and strain sign if the deformation is dominated by twinning, while they are usually different with respect to the loading conditions if the dislocation slip is dominant. The extension twinning under tension exhibits a similar behavior to that under compression, presumably due to the same Schmid stress introduced on the twinning plane along the twinning shear direction. However, the distribution of basal poles within the twins under tension is closely related to the initial texture, while they are always aligned with the compressive axis under compression. The low-cycle fatigue resistances follow the empirical Basquin and Coffin-Manson relationships with the texture dependency observed, related to the different activation sequences of twinning and detwinning involved, respectively, under tension and compression determined by the initial texture. Specifically, the post-detwinning deformation characteristics may be an important factor in understanding the texture dependency. The extension twinning is readily activated if an applied stress/strain supports c-axis extension of the hexagonal-close-packed (hcp) structure. The unique reorientation of the twins facilitates detwinning in the twinned areas during the subsequent strain/stress reversal. Therefore, the cyclic plastic deformation is dominated by the alternating twinning and detwinning, and the initial texture is recovered once detwinning capability is exhausted, concurrent with the disappearance of twin bands. In particular, detwinning occurs almost immediately in the twinned grains upon unloading, which is driven by the local tensile stress along their c-axes as a result of the stress redistribution between the soft- and hard-grain orientations due to the plastic anisotropy.
Author: Wei Wu (Materials scientist)
Publisher:
ISBN:
Category : Deformations (Mechanics)
Languages : en
Pages : 191
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Book Description
Author: Domonkos Tolnai
Publisher: MDPI
ISBN: 3036511024
Category : Science
Languages : en
Pages : 118
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Book Description
Due to their lightweight and high specific strength, Mg-based alloys are considered as substitutes to their heavier counterparts in applications in which corrosion is non-relevant and weight saving is of importance. Furthermore, due to the biocompatibility of Mg, some alloys with controlled corrosion rates are used as degradable implant materials in the medical sector. The typical processing route of Mg parts incorporates a casting step and, subsequently, a thermo–mechanical treatment. In order to achieve the desired macroscopic properties and thus fulfill the service requirements, thorough knowledge of the relationship between the microstructure, the processing steps, and the resulting property profile is necessary. This Special Issue covers in situ and ex situ experimental and computational investigations of the behavior under thermo–mechanical load of Mg-based alloys utilizing modern characterization and simulation techniques. The papers cover investigations on the effect of rare earth additions on the mechanical properties of different Mg alloys, including the effect of long-period stacking-ordered (LPSO) structures, and the experimental and computational investigation of the effect of different processing routes.
Author: Ashutosh Jain
Publisher: LAP Lambert Academic Publishing
ISBN: 9783843376013
Category :
Languages : en
Pages : 156
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Book Description
The role of twinning in the anisotropic behavior and ductility of magnesium alloys is analyzed at ambient as well as elevated temperatures. Magnesium alloy AZ31B sheet is investigated as a model system, because it is the most common wrought magnesium alloy. Uniaxial compression tests are conducted at room temperature and at elevated temperatures to measure the anisotropy of the strength and strain at various strain levels.A viscoplastic self-consistent polycrystal modeling approach was used to model the deformation behavior; including the anisotropy and texture evolution. Temperature dependence of parameters affecting activity of different deformation modes, such as Critical Resolved Shear Stress (CRSS) and strain hardening, and the volume fraction of twinned grains are investigated with the help of the polycrystal plasticity model.The model, thus developed, could find application for predicting material s response in complex loading conditions.
Author: J. Brian Jordon
Publisher: Springer Nature
ISBN: 3030366472
Category : Technology & Engineering
Languages : en
Pages : 400
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Book Description
The Magnesium Technology Symposium, the event on which this collection is based, is one of the largest yearly gatherings of magnesium specialists in the world. Papers represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. Magnesium Technology 2020 covers a broad spectrum of current topics, including alloys and their properties; cast products and processing; wrought products and processing; forming, joining, and machining; corrosion and surface finishing; and structural applications. In addition, there is coverage of new and emerging applications.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Yi Wang (Researcher in materials science and engineering)
Publisher:
ISBN:
Category : Anisotropy
Languages : en
Pages : 376
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Book Description
The combined effects of texture and grain size on the yielding and hardening behavior in a hot-rolled AZ31B Mg alloy were studied by using synchrotron x-ray diffraction and visco-plastic self-consistent (VPSC) simulation methods. First, the influence of texture on Hall-Petch relationships (namely, critical resolved shear stresses and hardening parameters) in a Mg alloy was investigated to establish a constitutive basis for the VPSC simulation. Then, the changes in dominant deformation mechanisms (basal, prismatic, and pyramidal slip as well as extension twin) and their relative interactions were studied systematically as a function of the initial texture using a VPSC scheme. The simulation results provide basic understanding of the effect of texture on the hardening behaviors in terms of the interaction of various active deformation mechanisms. Subsequently, the interplay between the texture and grain size effects on the activation of multiple deformation mechanisms and the plastic anisotropy was studied by incorporating the Hall-Petch Relationship in the VPSC modeling scheme. Finally, the influence of {1012} extension twin on the texture and microstructure evolution was investigated to understand physical implications of the simulation results. Specifically, the hardening anisotropy introduced by extension twin was studied with a focus on dislocation-twin interactions in terms of texture hardening, size hardening, and glissile-to-sessile transition hardening. The current study provides a basic micromechanical understanding of the effects of complex interactions among texture, loading path, and grain size on the yielding and hardening behavior of a wrought Mg alloy through plasticity simulations and diffraction measurements. The results would help improving the formability and advancing manufacturing techniques of wrought Mg alloy components for structural applications.
Author: Zhenzhen Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 148
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Book Description
In this thesis, the relationship among friction stir processing (FSP) parameters, microstructure evolution, texture development, and mechanical hehavior[sic] of AZ31B Mg alloy was investigated. First of all, in order to reveal the correlation among the deformation conditions, dynamic recrystallization (DRX) mechanisms, and microstructure evolution in the Mg alloy, hot compression tests at a wide range of Zener-Hollomon parameter (Z) values were conducted. Through optical microscopic examination, it was found out that above a critical Z value, twinning influences the DRX process resulting in a more effective grain refinement, which is manifested in a significant change in the slope of the Z-d[subscript rec] relationship, where d[subscript rec] is the recrystallized grain size. Moreover, EBSD examination revealed that the twinning also contributed to a distinct change in the recrystallization texture. Compression tests were performed along both through-thickness and in-rolling-plane directions of the plate to study the orientation dependency of twinning activities and its influence on the DRX process. X-ray line profile analysis (XLPA) provides further insights by highlighting the differences in the dislocation density/types, subgrain sizes, and twin densities during the DRX processes operating with or without the twinning. Secondly, the constitutive behaviour study was applied to the investigation of microstructure evolution during FSP. By varying the key FSP parameters systematically, i.e. rotation and travel rates of the tool, a series of FSP specimens were prepared with a wide range of thermo-mechanical inputs in terms of Z. The resulting tensile behavior in the stir zone (SZ) showed a dramatic change as a function of Z, caused by a systematic change in the texture within SZ measured by neutron diffraction. A three-dimensional transient model was developed to investigate the detailed deformation history including the temperature and strain rate profiles and material flow pattern during FSP of the Mg alloy. Such deformation history can be combined with the constitutive study from the compression tests in order to analyze the developments of micro-texture and DRX grains during FSP, which will, in turn, dominate the mechanical properties. Based on the studies above, new fundamental understandings were gained on the governing mechanisms for the deformation and recrystallization processes during FSP and the influence of thermo-mechanical input during FSP on ductility enhancement in the Mg alloy.
Author: Vineet V. Joshi
Publisher: Springer
ISBN: 3030057895
Category : Technology & Engineering
Languages : en
Pages : 355
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Book Description
The Magnesium Technology Symposium, the event on which this collection is based, is one of the largest yearly gatherings of magnesium specialists in the world. Papers represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. Magnesium Technology 2019 covers a broad spectrum of current topics, including alloys and their properties; cast products and processing; wrought products and processing; forming, joining, and machining; corrosion and surface finishing; and structural applications. In addition, there is coverage of new and emerging applications.
Author: Amanda J. Levinson
Publisher:
ISBN:
Category : Materials science
Languages : en
Pages : 380
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Book Description
The quasi-static mechanical response of annealed, highly textured AZ31 rolled plate was measured in simple compression on two sample directions, each promoting a different twin family. A high plastic anisotropy with extreme strain hardening in both directions was observed. New insights on the influence of both twin types to this behavior were derived by correlating changes in the strain hardening rates with the microstructure evolution. Extension twins nucleated at low strains, grew to consume most of the structure, and saturated at strains below the peak hardening rates. Thin contraction twins were initially postulated to be responsible for the peak hardening rates by limiting the hard pyramidal c+a slip length (producing a Hall-Petch type strengthening). However, subsequent experimental investigations raised questions on whether these are not present at the spacing required to account for the peak hardening rate. Thus, neither twin family was deemed responsible for the peak strain hardening rates. The effect of grain size on deformation twinning during strain hardening was also investigated by producing a similarly textured AZ31 plate with a larger grain size. A lower twinning stress was confirmed in this material. An additional change in strain hardening rate was associated with the nucleation of secondary extension twins forming perpendicular to the primary twin, limiting the growth potential of the pre-existing twins. The microstructure evolution during isothermal static annealing was investigated to critically evaluate the contributions of extension and contraction twins to the recrystallized microstructure after room temperature deformation, and establish the potential of these twins to alter the recrystallized texture. Contraction twins were potent sites for recrystallized nuclei producing many favorably oriented orientations for reduction of the strong c-axis fiber texture; while extension twins were not very effective in recrystallization. Recovery before the onset of recrystallization was extensive when the c-axis in most grains was compressed. Incomplete recrystallization within the hardest grains was deemed responsible for the retention of the c-axis fiber texture. These new insights were employed to identify the benefits of laser-roller hemming versus conventional hemming. Hemming is an automotive processing operation used to join inner and outer body panels involving severe forming and design requirements.
