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.
Author: Lan Jiang
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"The evolution of flow stress and microstructure during the deformation of two Mg-based (+Al, Mn, Zn) alloys has been studied under various conditions of temperature and strain rate. The tested materials were taken from AZ31 and AM30 extruded tubes. The effect of twinning was investigated by using uniaxial tension, uniaxial compression and ring hoop tension testing. Strain path change testing, i.e. tensile prestraining followed by uniaxial compression, was carried out to study the role of contraction and double twins on the subsequent deformation. Optical metallography and EBSD techniques were employed to study the microstructural development. The first part of the investigation focused on the flow stresses developed during deformation along the three different strain paths. It was found that at low temperatures (≤200°C), the flow behaviors are mainly controlled by twinning. At temperatures above 200°C but below 350°C, especially at a strain rate of 0.001s-1, the deformation is largely accommodated in partially dynamically recrystallized regions. As a result, the formation of voids in these regions causes premature fracture. The second part focused on the twinning behavior displayed during deformation to a strain of 0.15. The results indicate that the initial extrusion texture plays an important role in the formation of different types of twins and that the twinning behavior also depends on the strain path. {10-11} contraction and {10-11}-{10-12} double twinning are the dominant twinning mechanisms in uniaxial tension, while {10-12} extension twinning prevails in uniaxial compression and ring hoop tension testing. Grain size, temperature, strain and strain rate all have significant effects on the volume fraction of contraction and double twins. There is a sigmoidal relationship between the volume fraction of extension twins and the strain. The effect of grain size (in this grain size range) on the volume fraction of extension twins is small. For a given strain, at high strain rates, temperature does not have much influence on the volume fraction (below 200°C). In the third part of the investigation, the deformation texture associated with twinning was examined. The near 100% volume fraction of {10-12} extension twins gives rise to significant texture changes. By contrast, {10-11} contraction and {10-11}-{10-12} double twinning only make a small contribution to texture change due to the limited volume fraction of twinned material. Schmid factor analysis indicates that, for the {10-12} extension twins, all variants that are favorably oriented (i.e. with the highest SF values) can undergo rapid and complete twinning. For the {10-11} contraction twins, only variants in the TD component (11-20) 10-10 follow the SF criterion. The development of internal stresses, which somehow particularly affect the RD component (10-10) 0001 grains, may explain this difference. In the final part of the investigation, the effects of twinning on the strain hardening behavior and on ductility were studied. Different behaviors are shown to be responsible for the sharply contrasting strain hardening characteristics of the experimental flow curves. When a certain volume fraction (≥20% in the present study) is reached, contraction and double twinning generate net softening effects. Nevertheless, when they interact with extension twins, the hardening effect may predominate. On the other hand, extension twinning generally introduces a hardening effect. The hardening effect due to twin boundaries appears to be stronger than that from the volume fraction of extension twins, since the hardening associated with extension twinning cannot be explained by the volume fraction alone. Depending on the deformation conditions, twinning can be detrimental to the formability on the one hand but it can also be beneficial on the other."--
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: Christian Wetzel
Publisher: Cambridge University Press
ISBN: 9781558997790
Category : Technology & Engineering
Languages : en
Pages : 0
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Book Description
This book discusses GaN and Related Alloys and reflects an emerging emphasis on the binaries of InN and AlN. The major thrust here is the topical development of thin-film growth, bulk growth techniques, methods to cover the full ternary and quaternary alloy ranges toward InN and AlN and their characterization; strategies for structural defect reduction and their characterization; ways to better control p-type doping and its characterization; device and defect physics, including polarization effects; physics of surfaces and interfaces; and device processing techniques. In addition, advances in MBE devices, high-power electronics, RF performance of electronics, UV emitters, high-efficiency light emitters, photo and chemical sensors, as well as new applications within the group-III nitrides, are also covered. The book captures the current status of this field and will be useful for researchers working with group-III nitrides, as well as for students who seek entry into this subject.
Author: Suveen Mathaudhu
Publisher: Springer
ISBN: 3319480995
Category : Technology & Engineering
Languages : en
Pages : 609
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Book Description
This is a compilation of the best papers in the history of Magnesium Technology, a definitive annual reference in the field of magnesium production and related light metals technologies. The volume contains a strong topical mix of application and fundamental research articles on magnesium technology. Section titles: 1.Magnesium Technology History and Overview 2.Electrolytic and Thermal Primary Production 3.Melting, Refining, Recycling, and Life-Cycle Analysis 4.Casting and Solidification 5.Alloy and Microstructural Design 6.Wrought Processing 7.Modeling and Simulation 8.Joining 9.Corrosion, Surface Treatment, and Coating
Author: Martyn Alderman
Publisher: Springer
ISBN: 3319482319
Category : Technology & Engineering
Languages : en
Pages : 502
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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 in this collection represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. This volume 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; ecology; and structural applications. In addition, there is coverage of new and emerging applications in such areas as hydrogen storage.
Author: Jing Su
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Magnesium AZ31 alloy sheets were rolled at 100 °C at three different speeds: (i) 1000 m/min (high speed rolling, HSR), (ii) 100 m/min (intermediate speed rolling, MSR) and (iii) 15 m/min (low speed rolling, LSR). High reductions of more than 70% were achieved in single pass by HSR and MSR, while the sheet fractured at a reduction of only 37% by LSR. During HSR and MSR, dynamic recrystallization (DRX) was observed at reductions of 37% and higher, which was the mechanism for the greater rollability; DRX is, in turn, related to the higher temperatures generated. Full recrystallization was achieved at reductions higher than 70% during MSR and HSR. The dominant DRX mechanism was twinning/shear banding induced DRX, which led to partially recrystallized and twinned microstructures at reductions from 37% to 58%. Thus, fine recrystallized grains formed along the shear bands, which possessed much higher number of twins and accommodated more dislocation slips. In regions outside shear bands, the twin density was much lower, continuous recrystallization can be seen in twin free regions as well as at twins. For a given reduction, the maximum intensity of the basal texture is weaker after HSR than after LSR, which is due to the activation of a larger number of contraction and secondary twinning and/or c+a slip.The sheets were rolled at the high speed of 1000 m/min to six increasing reductions to generate a series of microstructures: (i) twinned and shear banded (8%-30%), (ii) partially DRXed and twinned (49%-58%) and (iii) fully DRXed (72%). These were annealed at temperatures from 200 °C to 500 °C for increasing time. As a comparison, the LSRed sheets were subjected to the same annealing conditions. Static recrystallization (SRX) kinetics were analyzed in terms of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model and found to involve two sequential annealing stages, characterized by two different Avrami exponents. Stage 1 is associated with recrystallization in the high stored energy regions, i.e. those containing shear bands and twins, while stage 2 concerns the recrystallization of the low stored energy regions. In the specimens subjected to low reductions (30%) and annealed at 200 °C for long time periods, some of the elongated grains remained unrecrystallized. This is attributed to the relative lack of formation of twins in these grains during rolling, i.e. to the very low stored energies in these regions. There was no significant difference in the microstructure evolution and recrystallization kinetics of the materials rolled at the two speeds. This is interpreted in terms of the Zener-Hollomon (Z) parameter, similar values of which applied to the two types of rolling and therefore to the microstructures produced. Static recrystallization of the heavily twinned and shear banded microstructures (produced at the reduction of 30%) led to significant texture weakening during annealing. The intensities of the basal texture of the HSRed specimens were lower than those of the LSRed specimens at all annealed conditions. This is due to the higher amount of contraction twins and more
Author: Colleen Bettles
Publisher: Elsevier
ISBN: 0857093843
Category : Technology & Engineering
Languages : en
Pages : 478
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Book Description
This important book summarises the wealth of recent research on our understanding of process-property relationships in wrought magnesium alloys and the way this understanding can be used to develop a new generation of alloys for high-performance applications.After an introductory overview of current developments in wrought magnesium alloys, part one reviews fundamental aspects of deformation behaviour. These chapters are the building blocks for the optimisation of processing steps covered in part two, which discusses casting, extrusion, rolling and forging technologies. The concluding chapters cover applications of wrought magnesium alloys in automotive and biomedical engineering.With its distinguished editors, and drawing on the work of leading experts in the field, Advances in wrought magnesium alloys is a standard reference for those researching, manufacturing and using these alloys. - Summarises recent research on our understanding of process-property relationships in wrought magnesium alloys - Discusses the way this understanding can be used to develop a new generation of alloys for high-performance applications - Reviews casting, extrusion, rolling and forging technologies, fundamental aspects of deformation behaviour, and applications of wrought magnesium alloys in automotive and biomedical engineering
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: Guozheng Kang
Publisher: John Wiley & Sons
ISBN: 1119180805
Category : Technology & Engineering
Languages : en
Pages : 320
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Book Description
New contributions to the cyclic plasticity of engineering materials Written by leading experts in the field, this book provides an authoritative and comprehensive introduction to cyclic plasticity of metals, polymers, composites and shape memory alloys. Each chapter is devoted to fundamentals of cyclic plasticity or to one of the major classes of materials, thereby providing a wide coverage of the field. The book deals with experimental observations on metals, composites, polymers and shape memory alloys, and the corresponding cyclic plasticity models for metals, polymers, particle reinforced metal matrix composites and shape memory alloys. Also, the thermo-mechanical coupled cyclic plasticity models are discussed for metals and shape memory alloys. Key features: Provides a comprehensive introduction to cyclic plasticity Presents Macroscopic and microscopic observations on the ratchetting of different materials Establishes cyclic plasticity constitutive models for different materials. Analysis of cyclic plasticity in engineering structures. This book is an important reference for students, practicing engineers and researchers who study cyclic plasticity in the areas of mechanical, civil, nuclear, and aerospace engineering as well as materials science.
