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1
Carter, Ellen Angharad. "High Current Anodization of Magnesium and Magnesium Alloys." Thesis, University of Auckland, 1996. http://hdl.handle.net/2292/2289.
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High current anodization of magnesium and magnesium alloys Ellen Angharad Carter Pure magnesium and three magnesium alloys containing different amounts of aluminium (2-9%) plus zinc and manganese were anodized with constant current density in sodium hydroxide solution with and without fluoride or phosphate ions. Electric field strengths of resultant anodic films were calculated from galvanostatic transients. These transients showed three characteristic features: linear voltage increase, noisy high voltage signals accompanied by sparking, and sawtooth-like events characterized by instantaneous voltage drops followed by slower voltage increases. Each feature was linked to certain physical processes occurring in the metal/film/solution system. Oxidation of magnesium and magnesium alloys formed anodic films with bilayer structures: a passive barrier layer adhering to the metal electrode, topped by a porous secondary layer. Cation injection into the barrier film across the metal/oxide interface was the rate determining step for film growth. Interstitial cations migrated through the film under the influence of the electric field. At the film/solution interface they reacted with electrolyte species and either thickened the film or dissolved in solution. Electric field strength was constant for particular metal/solution combinations and was independent of applied current density. Changing the electrode material altered the resultant electric field strength: pure magnesium produced oxides with lower electric field strengths than films formed on the three magnesium alloys. Changing the electrolyte had no discernable effect on the electric field strength. Charge efficiency of the film growth process was investigated by oxygen gas evolution; efficiency decreased during sparking. Ion beam analysis (Rutherford backscattering, fluorine depth profiling and nuclear reaction analysis) coupled with X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction studies and Raman spectroscopy gave information about the anodic film surface. These techniques showed that oxides formed on magnesium-aluminium alloys were thinner than those formed on pure magnesium caused by aluminium dissolution. Fluorine depth profiling revealed that concentration profiles for fluorine in anodic oxides formed in fluoride-containing solution altered depending on the aluminium content of the electrode material.
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Sato, Takanori. "Power-law creep behaviour in magnesium and its alloys." Thesis, University of Canterbury. Mechanical Engineering, 2008. http://hdl.handle.net/10092/1576.
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Creep is a time-dependent deformation of materials under stress at elevated temperatures.
The phenomenon of creep allows materials to plastically deform gradually over time, even
at stress levels below its yield point or below its transformation temperature. The issues
involving creep are especially significant for magnesium alloys, since they are susceptible
to creep deformation from temperatures as low as 100 ºC, which inhibits their potential
application in areas such as automotive engines.
The University of Canterbury has developed a significant level of experience and
infrastructure in the field of Electron Backscatter Diffraction (EBSD). EBSD allows
microstructures to be characterized by imaging the crystal structure and its crystallographic
orientation at a given point on a specimen surface, whereby the process can be automated
to construct a crystallographic “orientation map” of a specimen surface. In light of this, the
creep of magnesium and its alloys was studied using a novel technique, in which a
conventional tensile creep test was interrupted at periodic intervals, and the EBSD was
used to acquire the crystallographic orientation maps repeatedly on a same surface location
at each interruption stages. This technique allows simultaneous measurement of the rate of
creep deformation and the evolution of the specimen microstructure at various stages of
creep, bringing further insight into the deformation mechanisms involved.
This thesis summarizes the study of the microstructural and crystallographic texture
evolution during creep of pure magnesium and a creep resistant magnesium alloy Mg-
8.5Al-1Ca-0.3Sr. Pure magnesium exhibit a conventional “power-law” type creep, and
although its creep properties are well established in the past literatures, there has been little
in terms of reconciliation between the observed creep rates and the underlying deformation
mechanisms. The alloy Mg-8.5Al-1Ca-0.3Sr, on the other hand, is a modern die casting
alloy used in the automotive industry for engine and gearbox applications, and despite its
superior creep resistance, little is known about the microstructural contributions to its creep
properties.
This research was conducted to provide a link between the creep properties, observed
microstructures, and theories of creep deformation by the use of advanced microscopy
techniques. For the first time, the detailed, sequential microstructural development of
magnesium and its alloys during creep has been revealed.
3
Mwembela, Aaron Absalom. "Hot workability of magnesium alloys." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0003/NQ39793.pdf.
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Jiang, Bo. "Solidification behaviour of magnesium alloys." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/8407.
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Magnesium alloys have been extensively used for structural and functional applications due to their low densities. In order to improve the mechanical properties, grain refinement of the microstructures of magnesium alloys has been studied for many years. However, an effective and efficient grain refiner or refinement technique hasn’t been achieved yet, especially for those with aluminium contained. In this study, solution for this problem has been discovered through further understanding of the solidification process, including the potency and the efficiency of nucleation particles, the role of solute, and the role of casting conditions. First of all, the study suggested that MgO particles can act as nuclei in magnesium alloys by measuring and analyzing the differences in cooling curves with various amount of endogenous MgO particles. The differences indicated that the number density of MgO particles has a huge influence on the microstructure. This idea has been fatherly proved by the inoculation of MgO particles in magnesium alloys because the microstructures have been significantly refined after the inoculation. A new kind of refiner (AZ91D-5wt%MgO) has been developed based on such understandings. Secondly, the study discovered that the role of solute has much smaller effect on the grain size than it was suggested in traditional understandings. The inverse-proportional relationship between the grain size and the solute is highly suspected and the major role of solute is to cause columnar- equiaxed transition. The role of casting conditions has also been studied in order to provide experimental evidence for the existence of melt quenching effect in magnesium alloys. It is shown that various casting conditions, such as pouring temperatures and mould temperatures, have large influence on the critical heat balance temperature after rapid pouring. In this study, a theoretical model based on the analysis of cooling curves is presented for grain size prediction. An analytical model of the advance of equiaxed solidification front is developed based on the understanding of the role of casting conditions. Eventually, all these understandings have been applied to magnesium direct-chill (DC) casting. The refined microstructure of DC cast ingots can further assist in understanding the mechanism of advanced shearing achieved by MCAST unit. The comparison of the ingots with and without melt shearing indicated that the advance shearing device can disperse MgO film into individual particles.
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Lee, Young. "Grain refinement of magnesium /." St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16885.pdf.
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Ramírez, Anthony. "Ultrasonic grain refinement of magnesium alloys." Thesis, University of Portsmouth, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494007.
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The thesis project investigates ultrasonic grain refinement (UGR) of magnesium alloys. It commences with a brief study of the grain refinement of both aluminium-containing and aluminium-free magnesium alloys, by means of typical inoculating additives. That provides a basis for understanding the effectiveness of ultrasonic grain refinement of magnesium alloys to be presented in the following chapters.
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Hoffmann, Ilona. "MAGNESIUM-TITANIUM ALLOYS FOR BIOMEDICAL APPLICATIONS." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/36.
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Magnesium has been identified as a promising biodegradable implant material because it does not cause systemic toxicity and can reduce stress shielding. However, it corrodes too quickly in the body. Titanium, which is already used ubiquitously for implants, was chosen as the alloying element because of its proven biocompatibility and corrosion resistance in physiological environments. Thus, alloying magnesium with titanium is expected to improve the corrosion resistance of magnesium.
Mg-Ti alloys with a titanium content ranging from 5 to 35 at.-% were successfully synthesized by mechanical alloying. Spark plasma sintering was identified as a processing route to consolidate the alloy powders made by ball-milling into bulk material without destroying the alloy structure. This is an important finding as this metastable Mg-Ti alloy can only be heated up to max. 200C° for a limited time without reaching the stable state of separated magnesium and titanium. The superior corrosion behavior of Mg80-Ti20 alloy in a simulated physiological environment was shown through hydrogen evolution tests, where the corrosion rate was drastically reduced compared to pure magnesium and electrochemical measurements revealed an increased potential and resistance compared to pure magnesium. Cytotoxicity tests on murine pre-osteoblastic cells in vitro confirmed that supernatants made from Mg-Ti alloy were no more cytotoxic than supernatants prepared with pure magnesium. Mg and Mg-Ti alloys can also be used to make novel polymer-metal composites, e.g., with poly(lactic-co-glycolic acid) (PLGA) to avoid the polymer’s detrimental pH drop during degradation and alter its degradation pattern.
Thus, Mg-Ti alloys can be fabricated and consolidated while achieving improved corrosion resistance and maintaining cytocompatibility. This work opens up the possibility of using Mg-Ti alloys for fracture fixation implants and other biomedical applications.
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Sunseri, Erin Hannah. "Dendrite orientation in aluminum magnesium alloys." [Ames, Iowa : Iowa State University], 2009.
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Grace, Richard William. "Corrosion mechanisms and corrosion inhibition of commercial purity magnesium and advanced magnesium alloys." Thesis, Swansea University, 2012. https://cronfa.swan.ac.uk/Record/cronfa43082.
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Chama, Shadreck. "Mechanically alloyed aluminium-magnesium-lithium alloys : structure property relations." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399120.
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Freeney, Timothy Alan. "Friction stir processing of cast magnesium alloys." Diss., Rolla, Mo. : University of Missouri-Rolla, 2007. http://scholarsmine.mst.edu/thesis/pdf/Freeney_09007dcc804a9022_3_09007dcc8055e79b.pdf.
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Thesis (M.S.)--University of Missouri--Rolla, 2007.<br>Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed June 17, 2008) Includes bibliographical references.
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Barnackas, Irmantas. "Investigation of hydrogenation kinetics of magnesium and magnesium alloys in the ionized reactive atmosphere." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2008. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20080919_140633-22213.
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In the present work Mg and MgAl thin films were fabricated using physical vapour deposition (PVD) technologies as non-traditional and new nanotechnology methods for designing high performance hydrogen storage materials. The physical vapour deposition technologies allow the formation of metastable metal, alloy and chemical compounds with strictly controlled composition, microstructure and stoichiometry at low temperatures.
The synthesis of MgH2, MgAl and Mg(AlH4)2 films has been conducted in two steps: (i) fabrication of thin films employing magnetron sputtering in Ar gas, and (ii) hydrogenation of thin films employing plasma immersion ion implantation technologies.
For the first time, chemical compound Mg(AlH4)2 has been synthesized using the deposition of Mg and Al atoms from gas phase in hydrogen plasma (reactive deposition with simultaneously hydrogen implantation). The transformation of Mg thin film to MgH2 takes place at 400 K temperature during hydrogenation in hydrogen plasma. Experimental results showed that hydriding kinetics of Ti-doped Mg film increases and desorption temperature decreases by 60-80 K and the maximum H2-effusion from the Ti-undoped Mg-Al takes place at temperature 475 K, and for the Ti-doped Mg-Al film – at temperature 410 K; the release time of accommodated hydrogen is shorted for the Ti-doped Mg-Al film.
The mathematical model of hydrogenation shows that during the process of material irradiation in plasma the concentration of incident ions in... [to full text]<br>Šiame darbe, panaudojant jonines-plazmines technologijas, sintezuotos Mg, MgH2, Mg-Al ir Mg(AlH4)2 plonos nanokristalinės dangos. Ištirta jų struktūros, paviršiaus morfologijos ir sudėties priklausomybė nuo nusodinimo ir hidrinimo plazmoje technologinių parametrų. Darbe panaudoti plėvelių formavimo metodai: (i) magnetroninis-joninis garinimas Ar dujų aplinkoje; (ii) plonų dangų prisotinimas vandeniliu, panaudojant vandenilio jonų implantacijos iš plazmos technologijas.
Šio darbo originalumas susijęs su nepusiausvyrinių plazminių technologijų panaudojimu nanokristalinių medžiagų hidrinimui. Pirmą kartą atlikta metalų hidridų sintezė ir ištirta vandenilio kaupimosi kinetika nanostruktūrinėse medžiagose panaudojant plazminės vandenilio implantacijos technologiją. Gauti rezultatai patvirtina joninių-plazminių technologijų pranašumus, iš kurių svarbiausias - formuojamų plėvelių mikrostruktūros valdymas nanometriniame lygyje.
Tyrimo metu, panaudojant vandenilio jonų implantaciją į Mg-Al dangas, pirmą kartą susintezuotas Mg(AlH4)2 hidridas. 5 storio Mg dangų transformacija į MgH2, hidrinimo procesą atliekant vandenilio plazmoje, įvyksta esant 400 K temperatūrai. Eksperimentiniai rezultatai atskleidė, kad Ti priemaišomis legiruotose Mg dangose paspartėja hidridų formavimosi kinetika, o vandenilio desorbcijos temperatūra sumažėja 60-80 K. Vandenilio desorbcijos kinetika Ti priemaišomis legiruotose Mg-Al dangose taip pat yra spartesnė, o jų desorbcijos temperatūra sumažėja 65 K... [toliau žr. visą tekstą]
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Shi, Zhiming. "The corrosion performance of anodised magnesium alloys /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18391.pdf.
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Sanjari, Mehdi. "High strain rate deformation of magnesium alloys." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119590.
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The present study uses uniaxial compression testing over a wide range of strain rates to analyze the microstructure and texture evolution during high speed rolling (HSR) for AZ31B alloy and four Mg-Zn-Ce alloys. In the first part, the effects of strain rate on the flow behaviour and microstructure evolution on AZ31 Mg alloy were studied by compression testing over a wide range of strain rates (0.01-100 s-1) and temperatures (300-450 °C). In the second part, high-speed rolling of 1000 m/min was employed to successfully roll AZ31 alloy in one pass with 65% reduction in thickness at 300 °C and 450 °C. In the third part, a split Hopkinson pressure bar (SHPB) equipped with induction radiation furnace was used to attain a strain rate, in compression, of 1200s-1 in the temperature range of 25 to 350 °C and the result was compared with low strain rate (0.01 s-1) compression behavior. As well, during high-speed rolling at 500 m/min, the mill was interrupted, the sheet was withdrawn from rolling gap and the microstructure and texture evolution was investigated. In the final part, the recrystallization and texture evolution of four Mg-Zn-Ce sheets with a warm rolled microstructure obtained through two stages that can be characterised as rough rolling and finish rolling, was investigated at different stages of post-rolling annealing. The effect of rolling speed on the recrystallization and texture evolution of four Mg-Zn-Ce alloys was investigated as-deformed and after different stages of annealing. On annealing of Mg-Zn-Ce alloys, the same regions of the microstructure, located by hardness indentations, were examined and tracked by EBSD. Furthermore intragranular misorientation axes (IGMA) analysis was used to investigate the associated deformation mechanisms in the as deformed material. By combining these two methods, the development of the recrystallization microstructure was investigated and preferential nucleation sites, correlation between activated deformation mechanism and initial orientation of the recrystallized grains was studied. The IGMA analysis also shows that in Mg-1Zn-1Ce other types of dislocations rather than basal <a> are activated; in particular prismatic <a> type, is activated during deformation. Therefore the weakening of recrystallization texture during rolling resulting from the addition of RE elements is linked with a change in dynamic recrystallization (DRX) behaviour. Since the Mg-1Zn-1Ce alloy corresponds to the highest level of Ce in solid solution, the observed texture weakening is possibly due to decreasing grain boundary mobility as a result of solute partitioning of RE elements to dislocations and grain boundaries. The results showed that by increasing the rolling speed more secondary and compression twins were activated, which leads to the formation of more numerous local shear bands and a more uniform microstructure. The rotational dynamic DRX mechanism, in conjunction with the conventional DRX mechanism, is responsible for this texture weakening during high speed rolling.<br>La présente étude a été réalisée à l'aide d'essais par compression uni-axiale en utilisant une gamme variée de taux de déformation dans le but d'analyser la microstructure et l'évolution de la texture lors du procédé de laminage à haute vitesse pour les alliages de magnésium AZ31B et Mg-Zn-Ce. Dans la première partie, les effets du taux de déformation sur le comportement de l'écoulement et l'évolution de la microstructure de l'alliage AZ31B ont été étudiés par des essais de compression en utilisant une gamme variée de taux de déformation (0.01-100s-1) et des variations de la température de (300-450ºC).Dans la seconde partie de cette étude, le laminage à vitesse rapide (100m/min.) a été utilisé pour laminer l'alliage AZ31B avec succès dans une passe avec une réduction de l'épaisseur de 65% à 300C et 450ºC. Dans la troisième partie de ce projet, une unité d'essais Hopkinson (SHPB) équipée d'une fournaise à radiation a été utilisée afin d'atteindre un taux de déformation de 1200s-1 avec une gamme de température de 25 à 350ºC. Le résultat a été comparé avec le faible taux de déformation de (0.01s-1). De plus, au cours du laminage, à haute vitesse à 500 m/min., le laminoir a été arrêté, la feuille a été retirée des rouleaux, la microstructure et la texture ont été analysées.Des quatre alliages Mg-Zn-Ce, l'alliage Mg-1Zn-1Ce lequel avait le rapport Ce/Zn le plus élevé a démontré la plus faible texture telle que laminée et le rapport le plus homogène pour ce qui a trait au ratio pliage/maclage. En modifiant la teneur en zinc, la grosseur des particules a changée et pour les alliages démontrant un affaiblissement de la texture, le mécanisme de recristallisation a été modifié. Suite au recuit des alliages Mg-Zn-Ce, les sites identiques de la microstructure identifiés par des essais de micro dureté ont été examinés et suivis par EBSD. De plus, une analyse de la désorientation des axes inter granulaires (IGMA) a été effectuée afin d'analyser les mécanismes de déformation dans le matériel déformé. Ainsi à l'aide de la combinaison de ces deux méthodes, le développement de la microstructure recristallisée a été analysé et les sites préférentiels de nucléation, la corrélation entre les mécanismes de la déformation activée et l'orientation initiale des grains recristallisés ont été étudiés. La méthode d'analyse (IGMA) montre aussi que pour l'alliage Mg-1Zn-1Ce d'autres types de dislocations en plus de la structure de base < a > sont activés; en particulier le type prismatique < a > est activé au cours de la déformation. Par conséquent, l'affaiblissement de la texture de recristallisation au cours du laminage qui résulte de l'addition des éléments des terres rares est relié avec le comportement de la recristallisation dynamique. Alors que l'alliage Mg-1Zn-1Ce correspond à la plus haute teneur en Ce dans la solution solide, la texture affaiblie observée est possiblement reliée à la mobilité des bordures de grains comme résultant du fractionnement du soluté des éléments des terres rares pour les dislocations et les joints de grains. Les résultats ont montré qu'en augmentant la vitesse de laminage que plus de macles secondaires de compression ont été produites, ce qui a conduit à la création d'un plus grand nombre de bandes de cisaillement et une microstructure plus uniforme. Le mécanisme de recristallisation dynamique rotationnel en relation avec le mécanisme (DRX) est responsable de l'affaiblissement de la texture au cours du laminage à haute vitesse.
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Yang, Xinliang. "Particle dispersion in aluminium and magnesium alloys." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/14437.
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High shear mixing offers a promising solution for particle dispersion in a liquid with intensive turbulence and high shear rate, and has been widely used in the chemical, food and pharmaceutical industries. However, a practical high shear mixing process has not yet been adapted to solve the particle agglomeration in metallurgy due to the high service temperature and reactive environment of liquid metal. In this study, the effect of high shear mixing using the newly designed rotor-stator high shear device have been investigated with both Al and Mg matrix composites reinforced with SiC particles through casting. The microstructural observation of high shear treated Al and Mg composites show improved particle distribution uniformity in the as-cast state. Increased mechanical properties and reduced volume fraction of porosity are also obtained in the composite samples processed with high shear. With the melt conditioning procedure developed for twin roll casting process, two distinct solutions has been provided for thin gauge Mg strip casting with advanced microstructure and defect control. The melt conditioning treatment activates the MgO as heterogeneous nuclei of α-Mg through dispersion from continuous films to discrete particles. Thus enhanced heterogeneous nucleation in the twin roll casting process not only refines the α-Mg grain size but also eliminates the centre line segregation through equiaxed grain growth and localized solute distribution. The grain refinement of the α-Mg through SiC addition has also been studied through EBSD and crystallographic approaches. Two reproducible and distinct crystallographic orientation relationships between α-SiC (6H) and α-Mg have been determined: [1010]SiC//[2113]Mg, (0006)SiC//(1011)Mg, (1216)SiC//(2202)Mg and [0110]SiC//[1100]Mg, (0006)SiC// (0002)Mg, (2110)SiC//(1120)Mg.
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Chen, Xi. "Corrosion Resistance Assessment of Pretreated Magnesium Alloys." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1282837277.
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Thornton, Robert. "Magnesium alloys as a bioresorbable implant material." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/magnesium-alloys-as-a-bioresorbable-implant-material(62b9e43f-bdee-4d89-8dc5-04a6d0c2a8a4).html.
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The use of magnesium as a bioresorbable implant material has been gaining large amounts of interest over the last five years. Mg alloys by nature corrode rapidly comparative to other engineering metals, Mg is also naturally found in the body, meaning it offers a potential degradable material which can support far higher stresses than the current biodegradable polymers. Magnesium Elektron wanted to gain an understanding of how Mg alloys would work in this new environment and find a potential alloy fit for purpose. This thesis outlines the progress the author and Magnesium Elektron have made in achieving those goals. Initally, to form an understanding of what occurs when Mg is implanted into the body. Osteoblast trials were used to determine in vitro responses and effects on the various Mg alloys. These studies showed that high corrosion rates initially seen when Mg alloys are placed in cell culture medium have a lower cell numbers. Most likely due to local pH rise. The effect is inherent to all Mg alloys irrespective of their overall corrosion rate. However, after the initial corrosion spike, surviving cells on the surface would proliferate and attach well. The attached cells on Mg also showed a phenotype expression change compared to those on glass. It was then established that lowering the corrosion rate of the current Mg alloys was now key. Initially this involved modifications to current alloys. Annealing ML4 at 350°C for 8 hours was found optimal and lowered corrosion rates by 20-30%. Further work looked at modifing alloys by changes to chemical composition. It was discoveredd that additions of 8wt% Er to ML4 made corrosion rates drop by 6-8 times in SBF. Additions of Gd in ML4 also gave low corrosion, 2 times less than ML4. Calcium also lowered corrosion rates slightly. The modifications to the Mg surface was also looked into to lower the initial corrosion rate and potentially alter the biocompatibility of the alloys. Two successful techniques were found. Firstly organo-silanes were found to protect Mg for around 4 days, with reductions in corrosion rate of 6 times in the first hours. Silanes were also successfully used as anchors to graft polythene gycol to create a non fouling surface, which could protentially lower stent restenosis. Secondly, Magnetron sputtered hydroxyapatite was used to lower corrosion rates by 6 times in the first 24 hours with no visible hydrogen gas being evolved in the first hours.
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Behdad, Sadegh. "Novel Ternary Magnesium-Tin Alloys by Microalloying." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2313.
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The objective of this research was to explore the possibility of developing novel Magnesium-Tin alloys with improved mechanical properties by micro-alloying. Magnesium is the lightest of all structural metals. It can be machined faster and with almost half the power required for aluminum. There is a limitless supply of magnesium in sea water and it can also be recycled at 5% of initial energy requirements. These properties make magnesium an ideal green alternative to replace metals and polymers in automotive, aerospace, biomedical and defense sectors. The potential weight reduction in the US automotive market alone, leads to 100 billion gallons of gas saved and 6.5 billion gallons of CO2 emissions reduced per year.
In defense and aerospace markets, China is the leading foreign supplier of rare earth metals necessary for fabrication of current high-performance Mg alloys, making core defense technologies vulnerable to the interruption of Chinese imports. In the past, China has used its control over mining, application and import of rare earth metals as a strategic leverage. These new Magnesium-Tin ternary alloys offer an alternative that can be made from domestic resources improving national security and minimizing foreign dependence on rare earth metals import.
Our results establish that microalloying can tackle issues arising from sluggish precipitate formation kinetics and precipitate size distribution in binary Magnesium-Tin alloys. These new alloys also offer an order of magnitude reduction in heat treatment time (from approximately 1000 hours to less than 100 hours), which makes the benefits of their application two-fold by decreasing manufacturing energy costs and production time. This can also open the route for development of new age-hardenable wrought Magnesium alloys.
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Joshi, Utsavi Mukeshbhai. "Grain refinement in aluminium containing magnesium alloys." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/13681.
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The novel grain refiners developed in this research could be broadly classified into borides and carbides. The motive behind choosing MgB2, AlB2 and their master alloys Mg-MgB2 and Mg-AlB2 as the grain refiners was driven by the crystallographic matching of the hexagonal borides with the magnesium crystal structure. Apart from this lightweight borides, denser borides such as CrB and WB have also shown excellent grain refinement in AZ91, AM50 and AZ31 alloys. It is suggested that the grain refinement effect in the magnesium alloys could be improved through a combined addition of bismuth along with the boride. The carbon based grain refiners were also explored as they are well-established for the grain refinement of aluminium containing magnesium alloys. The new carbon based grain refiners identified through this research are B4C, Mg-B4C, Mg-3Ti-1C. Magnesium matrix was chosen for the development of each of these master alloys to eliminate any impurity contamination during the grain refiner addition to the magnesium melt. The pressureless melt infiltration techniques was involved in the development of Mg-MgB2, Mg-AlB2 and Mg-B4C while, the ‘halide salt route’ was adopted for producing Mg-3Ti-1C master alloys. The application of ultrasonic cavitation for the development of a new Al-1.5B-2C master alloy was shown to be effective for a homogenous distribution of the intermetallic phases in the form of Al3BC. The potential heterogeneous nucleating sites proposed in the commercial aluminium containing magnesium alloys are MgB2 for Mg-MgB2 master alloy; Mg1-xAlxB2 (0.10 < x < 0.18) for AlB2 grain refiner; MgB2C2 for B4C grain refiner; CrB and WB for their individual powder additions respectively; Ti2AlC for Mg-3Ti-1C master alloy; Al3BC and Al4C3 for the Al-1.5B-2C master alloy.
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Samuel, Ehab. "Serrated flow and enhanced ductility in coarse-grained Al-Mg alloys." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115867.
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Aluminum 5XXX alloys are of industrial importance and interest as they combine a wide range of desirable strength, forming and welding characteristics with a high resistance to corrosion. The presence of Mg in these alloys ensures favorable mechanical properties. However, the room temperature stretching performance of these alloys is limited. Moreover, Al-Mg alloys are known for being susceptible to the Portevin-LeChatelier effect when deformed at room temperature. Nevertheless, improvements in ductility can be achieved through warm forming, especially when the ductility approaches superplastic levels.<br>The aim of this study was to test for enhanced ductility in three coarse-grained Al-Mg alloys namely, super-pure Al-3%Mg and Al-5%Mg, and commercial AA 5056 alloy. The temperature-dependent flow stress and rate sensitivity behavior of these alloys was investigated by means of tensile testing using ASTM E8M-04 standard samples. Samples were deformed to 10% strain to allow enough deformation to occur such that serrations in the dynamic strain aging (DSA) temperature/strain rate range would be rendered visible on a stress-strain curve. Using this information, the regions of negative and higher-than-normal strain rate sensitivity ('m') were plotted and tensile tests to failure were performed in the vicinity of maximum 'm'. ASTM E2448-06 standard samples for superplasticity tensile testing were used in this case.<br>A maximum ductility of 170% was recorded with these samples and this was found to increase to nearly 300% when the gage length was shortened. It was observed that the DSA serrations were more prominent at lower strain rates, higher temperatures and higher Mg contents. The results of this study show clearly that if the rate sensitivity is high enough, then enhanced ductility in coarse-grained materials is possible at temperatures well below the maximum test temperature.
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Vespa, Geremi. "Hot deformation behavior of magnesium AZ31." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99796.
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Automobile manufacturers are interested in lightweight materials, including magnesium, to increase vehicle fuel economy, improve performance and reduce emissions. In this work the deformation behavior of as-cast and rolled magnesium AZ31 alloy has been studied. In as-cast material, it was found that reheating at 400°C and above for 60 minutes increased the homogeneity of the as-cast structure and gave rise to repeatable deformation. At compression temperatures above 300°C dynamic recrystallization occurred; below 200°C, there was significant twinning. Annealing completely recrystallized the structure deformed below 200°C, but did not change the dynamically recrystallized structure. AZ31 alloy was also rolled at temperatures of 350, 400 and 450°C and rolling speeds of 20 and 50 rpm for 15 and 30% reduction in thickness to produce sheet. Before rolling, the alloy was preheated for I and 10 hours at the rolling temperatures. The sheets were then tensile tested at 300, 400 and 450°C with strain rates of 0.1, 0.01 and 0.001s-1. The flow curves and microstructures indicated that the tensile deformation mechanism changed with processing conditions. Two deformation mechanisms were present in the magnesium sheet depending on the strain rate and grain size. At slow strain rates and small grain size, the active deformation mechanism was grain boundary sliding. As grain sizes increased there was also a component of dislocation creep. At the fast strain rate, the deformation mechanism, regardless of grain size, was dislocation creep. At a true strain rate of 0.001s-1, it was found that rolling at 350°C with 30% reduction per pass yielded the finest microstructure and subsequently, the best hot deformation characteristics. At a true strain rate of 0.1s-1, rolling at 450°C with 30% reduction per pass yielded a coarser, more recrystallized microstructure with best hot deformation characteristics.
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Syvertsen, Alf Petter. "Alloys as Anode Materials in Magnesium Ion Batteries." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16778.
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This thesis is a feasibility study of the possible application of magnesium alloys forfuture magnesium-ion batteries. It investigates dierent alloys and characterizesthem with respect to internal resistance, overpotentials and the reversibility of theelectrochemical reaction. SEM and EDS studies of used electrodes have also beencarried out. It has been showed that alloys, easier to handle and at a fraction of thecost, can be used with equal or better performance than pure Mg. The seeminglysuperior alloy, AZ61 exhibits a coloumbic eciency close to 100%, at higher chargerates than pure Mg.
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Çelikin, Mert. "The creep behaviour of Magnesium-Manganese based alloys." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110533.
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The concern for weight-reduction in vehicles has increased substantially in recent decades due to fuel consumption regulations. Extending the use of magnesium (Mg), the lightest structural metal, in automotive powertrain applications has been one of the routes to reduce vehicle weights. In this doctoral work, the creep behaviour of Mg-Mn based systems with cerium (Ce) and/or strontium (Sr) additions is studied in order to shed light into the new design principles for the development of creep-resistant Mg alloys. Transmission electron microscopy (TEM) is used to characterize the microstructures (the orientation, coherency, crystal structure and the morphology of the phases) as well as the features of creep deformation (twins, dislocations, sub-grains). In the Mg-Mn binary system, the dynamic precipitation of α-Mn was observed upon thermal exposure and during creep. Two different orientation relationships (OR) were determined between α-Mn (rods) precipitated upon heat treatment and the α-Mg matrix. The creep mechanisms were determined to be dislocational processes based on the activation energy (Qc) values (Qc (pure Mg) = 105 and 168kJ/mole; Qc (Mg-1.4Mn) = 127 and 154kJ/mole) obtained via long-term creep tests at different temperatures. The creep strengthening effect of Mn was due to the dynamic precipitation of α-Mn on dislocations (acting as heterogeneous nucleation sites) during creep. In the Mg-Ce-Mn ternary system, the intradendritic precipitation of Mg12Ce occurred heterogeneously where α-Mn precipitates acted as nucleants. The nucleation and growth of the α-Mn and Mg12Ce precipitates were mutually affected by the presence of the other. The dislocational processes were found to be rate-controlling, hence, the refinement in the Mg12Ce precipitate size via α-Mn precipitates enhanced the creep resistance by providing effective dislocation pinning. In the Mg-Sr-Mn ternary system, a new orientation relationship (OR) was determined between the Mg17Sr2 and α-Mn phases, which resulted in differing morphologies of the dynamically precipitated α-Mn depending on the region of precipitation (interdendritic and intradendritic regions). Creep deformation was again found to be dependent on dislocational processes: pipe diffusion at low temperatures and either dislocation climb or activated cross-slip at the higher temperatures (Qc (JM51) = 99 and 234kJ/mole; Qc (JM52) = 93 and 135kJ/mole). The dynamic precipitation of α-Mn on the basal dislocations of the intradendritic regions enhanced creep resistance via pinning by coherency strain fields. Mg-Sr-Mn-Ce alloys exhibiting high creep resistance were developed. The design principles were based on the results obtained from the creep behaviour studies of the pure Mg, Mg-Mn, Mg-Ce-Mn, Mg-Sr-Mn systems, as well as thermodynamic calculations by FactSage. The microstructure of the alloys consisted of the Mg17Sr2 intermetallic phase at the interdendritic regions which strengthened the grain boundaries, and dissolved Mn and Ce which resulted in the dynamic co-precipitation of Mg12Ce and α-Mn (Sr) in intradendritic regions during creep. The creep strain of the quaternary alloys was around to be four times lower than the strain of the ternary alloys.<br>L'intérêt pour la réduction du poids des véhicules automobiles a augmenté de façon significative au cours de la présente décennie principalement à cause des restrictions sur la consommation d'essence. L'augmentation de l'utilisation du magnésium (Mg), le métal structurel le plus léger, pour les applications automobiles, les composantes des groupes propulseurs, a ainsi été une des avenues utilisées pour solutionner le problème de réduction de poids des véhicules. Dans ce travail de doctorat, le comportement au fluage des systèmes de base Mg-Mn avec des additions de cérium (Ce) et/ou de strontium (Sr) est étudié afin de faire la lumière sur de nouveaux principes de développement d'alliages de magnésium résistant au fluage. La microscopie à transmission électronique (MET) est utilisée pour caractériser les microstructures (l'orientation, la cohérence, la structure cristalline et la morphologie des phases) ainsi que les caractéristiques des déformations provoquées par le fluage (mâcles, dislocations, sous-grains). Dans le système binaire Mg-Mn, une précipitation dynamique de la phase α-Mn a été observée suite à une exposition thermique et au cours du fluage. Deux différentes relations d'orientation (OR) ont été déterminées entre les tiges de α-Mn qui ont précipitées suite au traitement thermique et dans la matrice α-Mn. Les mécanismes de déformation au fluage ont été déterminés comme étant des procédés basés sur les valeurs de l'activation d'énergie (Qc), Qc Mg pur = 105 et 168kJ/mole; Qc Mg-1.4Mn = 127 et 154kJ/mole, obtenues par le biais d'essais de fluage effectués à long terme à différentes températures. L'effet de renforcement au fluage du Mn a été causé par la précipitation dynamique de la phase α-Mn sur les dislocations agissant ainsi comme des sites de nucléation lors du fluage. Dans le système ternaire Mg-Ce-Mn, une précipitation interdendritique de Mg12Ce a été produite de façon hétérogène à l'endroit où les précipités α-Mn ont agits comme agents de nucléation. La nucléation et la croissance des précipités α-Mn et Mg12Ce ont été affectées mutuellement par la présence de l'un et de l'autre. Les procédés de dislocation ont donc été trouvés par conséquent comme étant un taux de contrôle, le raffinement de la grosseur du précipité Mg12Ce via les précipités α-Mn qui a amélioré la résistance au fluage par l'approvisionnement d'une méthode effective de fixation des dislocations. Dans le système ternaire Mg-Sr-Mn, une nouvelle relation d'orientation a été déterminée entre les phases Mg17Sr2 et α-Mn qui a résulté dans la différentiation de morphologies du précipité α-Mn en fonction de la région de précipitation (régions interdendritiques et intradendritiques). La déformation au fluage a été trouvée dépendante des procédés de disclocations: diffusion de défauts à basse température et l'un ou l'autre de la montée de dislocation ou des glissements activés entrecroisés à une température plus élevée (Qc (JM51) = 99 et 234 kJ/mole; Qc (JM52) = 93 et 135 kJ/mole). La précipitation dynamique de la phase α-Mn sur les dislocations de base des régions interdendritiques a amélioré la résistance au fluage par le biais de la fixation des champs d'allongement cohérents. Les alliages Mg-Sr-Mn-Ce démontrant une résistance élevée au fluage ont été développés. Les principes de conception ont été basés sur les résultats à partir du comportement au fluage des systèmes, Mg pur, Mg-Mn, Mg-Ce-Mn et Mg-Sr-Mn ainsi que des calculs thermodynamiques effectués à partir de la méthode FactSage. La microstructure des alliages a été constituée de la phase intermétallique Mg17Sr2 aux régions interdendritiques qui ont renforcé les bordures de grains et qui ont dissout le Mn et le Ce lesquels ont favorisé la co-précipitation dynamique de Mg12Ce et α-Mn dans les régions intradendritiques pendant le fluage. Les allongements obtenu lors du fluage des alliages quaternaires ont été quatre fois plus bas que les allongements des alliages ternaires.
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Masoumi, Mohsen. "Microstructure and texture studies on magnesium sheet alloys." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104722.
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The AZ3, the most common Mg sheet alloy, is currently produced by hot rolling of the DC cast ingot. Mg wrought alloys, in general have limited formability due to hexagonal close-packed structure and preferred orientation (texture). In order to improve magnesium sheet formability, a good understanding of microstructure and texture evolution in twin-roll casting is necessary. The objectives of this research are to study the microstructural and texture evolution in twin-roll cast AZ31 Mg sheet alloy and to develop/modify alloy compositions with improved mechanical properties (weakened texture). In the first part of study, the influence of cooling rate (CR) on the casting structure of AZ31 magnesium alloy has been investigated, as a background to understand microstructural development in TRC AZ31, using different moulds to obtain slow to moderate cooling rates. It was found that grain size and secondary dendrite arm spacing (SDAS) reduces as the cooling rate increases. Moreover, it was observed that with an increase in cooling rate the fraction of second phase particles increases and the second phase particles become finer. The second part focused on the microstructure and texture study of the twin-roll cast (TRC) AZ31 (Mg-3wt.%Al-1wt.%Zn) sheet. The results indicate that TRC AZ31 exhibits a dendritic microstructure with columnar and equiaxed grains. It was noted that the amount of these second phases in the TRC alloy is greater than the conventionally cast AZ31. Recrystallization at 420 oC leads to a bimodal grain-size distribution, while a fine-grain structure is obtained after rolling and annealing. The TRC AZ31 sheet exhibits basal textures in the (i) as-received, (ii) rolled and (iii) rolled-annealed conditions. However, post-annealing of the TRC AZ31 at 420 oC produces a relatively random texture that has not been previously observed in the conventional AZ31 sheet. The texture randomization is attributed to the particle-stimulated nucleation (PSN) of new grains in the TRC structure. The preliminary evaluation of mechanical properties indicates that such annealing treatment slightly increases the ultimate tensile strength (UTS), but significantly improves elongation. In the final of part of the study, the microstructures and textures of rolled and rolled/annealed Mg-1wt.%Mn-based and Mg-1wt.%Zn-Based alloys containing different levels of Ce and Sr were examined. The Ce addition refines the as-cast and rolled/annealed grain structure of Mg-1wt.%Mn (M1) alloy. Moreover, the overall texture intensity of basal pole was weakened for rolled as well as rolled/annealed Mg-Mn-Ce alloys compared to the M1 alloy. The texture weakening was attributed to the solid solubility of Ce in Mg rather than PSN or c/a ratio alteration. The Sr addition refined the as-cast and rolled/annealed grain structure of Mg-1wt.%Mn-Sr (MJ) and Mg-1wt.%Zn (Z1) alloy. Moreover, the overall texture intensity of basal pole was weakened for rolled as well as rolled/annealed Mg-Zn-Sr (ZJ) alloys compared to the Z1 alloy. The texture weakening is attributed to the PSN of new grains with random orientations.<br>Le AZ3, l'alliage Mg les plus courantes de feuille, est actuellement produite par laminage à chaud de l'lingot coulé DC. Alliages de magnésium forgé, en général, ont limité en raison de la formabilité hexagonale compacte structure et l'orientation préférentielle (texture). Afin d'améliorer la formabilité feuille de magnésium, une bonne compréhension de la microstructure et l'évolution de texture dans la coulée entre cylindres est nécessaire. Les objectifs de cette recherche sont d'étudier l'évolution de la microstructure et de texture dans deux cylindres en alliage fonte AZ31 feuille de Mg et de développer / modifier des compositions d'alliages avec des propriétés mécaniques améliorées (texture affaibli). Dans la première partie de l'étude, l'influence de la vitesse de refroidissement (CR) sur la structure coulée en alliage de magnésium AZ31 des a été étudiée, comme un fond pour comprendre le développement des microstructures du TRC AZ31, en utilisant des moules différents pour obtenir lente à modérée des taux de refroidissement. On a constaté que la taille des grains et secondaire espacement des bras de dendrite (DPS) diminue à mesure que les augmentations de taux de refroidissement. Par ailleurs, il a été observé que, avec une augmentation du taux de refroidissement de la fraction de particules de seconde phase augmente et les particules de seconde phase deviennent plus fins. La seconde partie a porté sur la microstructure et la texture d'étude de la distribution à double rouleau (TRC) AZ31 (% Mg-3wt. Al-1wt.% Zn) feuille. Les résultats indiquent que la TRC AZ31 présente une microstructure dendritique avec colonnaires et de grains équiaxe. Il a été noté que le montant de ces phases secondes dans l'alliage TRC est supérieure à la AZ31 conventionnellement exprimés. Recristallisation à 420 ° C conduit à une bimodale granulométrie, alors qu'une structure à grains fins est obtenue après laminage et recuit. La feuille de TRC AZ31 expositions textures basale dans le (i) que nous avons reçues, (ii) roulé et (iii) laminé recuit conditions. Cependant, le post-recuit de l'AZ31 TRC à 420 oC produit une texture relativement aléatoire qui n'a pas été observé précédemment dans le conventionnelles AZ31 feuille. La randomisation texture est attribuée à la particule stimulée par la nucléation (PSN) de nouveaux grains dans la structure de la TRC. L'évaluation préliminaire des propriétés mécaniques indique que ces traitements de recuit augmente légèrement la résistance à la traction (UTS), mais améliore significativement l'allongement. Lors de la finale d'une partie de l'étude, les microstructures et les textures des laminés et laminé / recuits Mg-1wt.% Mn et Mg-basée 1wt.% Zn-alliages à base contenant les différents niveaux de Ce et Sr ont été examinés. L'ajout Ce affine la structure du grain de coulée et roulé / recuit de Mg-1wt.% Mn (M1) en alliage. Par ailleurs, l'intensité de la texture globale pôle basal a été affaiblie par laminé ainsi que laminé / recuits Mg-Mn-Ce alliages par rapport à l'alliage M1. L'affaiblissement texture a été attribué à la solubilité solide de Cé en Mg plutôt que PSN, ou c / une altération ratio. L'ajout de Sr raffinée que la structure des grains-coulés et laminés / recuit de Mg-1wt.% Mn-Sr (MJ) et Mg-1wt.% Zn (Z1) alliage. Par ailleurs, l'intensité de la texture globale pôle basal a été affaiblie par laminé ainsi que laminé / recuits Mg-Zn-Sr (ZJ) alliages par rapport à l'alliage Z1. L'affaiblissement texture est attribué au PSN de nouveaux grains d'orientations aléatoires.
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Ebeling, Timo [Verfasser]. "Plastic Deformation Modeling of Magnesium Alloys / Timo Ebeling." Aachen : Shaker, 2010. http://d-nb.info/1122546262/34.
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Jia, Jimmy Xueshan. "Computer modelling of galvanic corrosion of magnesium alloys /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18932.pdf.
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Garboggini, Araripe do Amaral. "Structure and properties of rapidly solidified magnesium alloys." Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313041.
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Henry, Dominic Thomas. "Particle Effects on Recrystallisation in Wrought Magnesium Alloys." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503003.
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Van, Pelt Jacqueline G. Shaw Barbara A. "Magnesium alloys for use in bioabsorbable cardiac stents." [University Park, Pa.] : Pennsylvania State University, 2009. http://honors.libraries.psu.edu/theses/approved/WorldWideIndex/EHT-6/index.html.
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Esho, Faris Nora. "Creep Properties of Magnesium Alloys AE44 and AZ91." Thesis, Högskolan i Jönköping, Tekniska Högskolan, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-44261.
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Bhat, Panemangalore Devadas. "Development of magnesium-based alloys for biomedical applications." Thesis, Lille, 2019. http://www.theses.fr/2019LIL1R002.
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Étant donné leur capacité à se dégrader à l'intérieur du corps, les implants biodégradables ont fait l'objet de nombreuses recherches médicales. Parmi tous les matériaux, c'est le magnésium, un élément indispensable du corps humain, qui conduit aux résultats les plus favorables car son module d'Young est similaire à celui de l'os. De ce fait, les méthodes adoptées afin d'améliorer le comportement du magnésium pur vis-à-vis de la corrosion sont les suivantes: a)Ajout d'éléments d'alliage comme le zinc, le calcium et l'erbium (Mg-2Zn-2Er, Mg-2Zn-0.6Ca-1Er, etc.) pour contrôler le comportement de dégradation b) Procédés secondaires tels que l'extrusion pour modifier sa microstructure c)Revêtements de surface à base de fluorure pour mieux protéger la surface. La première partie de cette thèse porte sur la caractérisation microstructurale d'alliages. La caractérisation microstructurale révèle la présence de MgZn2, de phases W (Mg3Zn3Er2) et i (Mg3Zn6Er) dans différents alliages. L'évaluation des propriétés mécaniques a révélé une augmentation des propriétés de traction et de compression des alliages ternaires et quaternaires par rapport aux alliages de Mg et de Mg-2Zn. Ces propriétés mécaniques améliorées sont attribuées à une réduction de la taille des grains, à la présence d'atomes de soluté et à des phases secondaires. Mg-2Zn-2Er et Mg-3Zn-0.5Er présentaient une résistance à la corrosion améliorée en raison de la microstructure à granulométrie fine et d'une répartition uniforme des phases secondaires. La viabilité cellulaire a été améliorée avec l'épaisseur du temps de revêtement et ces alliages pourraient servir de candidats potentiels pour d'autres tests in vivo<br>With the ability to bio-degrade and thereby reducing the stress-shielding effect, biodegradable implants are of great importance in medical research. Among all the materials, magnesium is the one which shows promising results being bio-degradable and with the properties comparable with its young's modulus to that of bones. In the present study, the approaches adopted to improve the mechanical and corrosion behaviors of pure magnesium using carefully chosen: (a) Alloying elements like zinc, calcium and erbium (Mg-2Zn-2Er, Mg-2Zn-0.6Ca-1Er, etc.) to control the degradation behavior (b) Secondary processes like extrusion to alter and improve the microstructure (c) Surface treatments like fluoride coatings to further protect the surface to resist the rapid dissolution. The first part of this thesis focuses on the microstructural characterization of as-DMDed and as-extruded alloys. The microstructural characterization (XRD and TEM) reveals the presence of MgZn2, W-phase (Mg3Zn3Er2) and i-phases (Mg3Zn6Er) in different alloys. The mechanical property assessment revealed an increment in the tensile and compressive properties of ternary and quaternary alloys as compared to pure Mg and Mg-2Zn binary alloy. These values are attributed to a reduction in grain size, presence of solute atoms and secondary phases. Mg-2Zn-2Er and Mg-3Zn-0.5Er showed enhanced corrosion resistance due to the fine grain sized microstructure and a uniform distribution of secondary phases. The cell viability values were enhanced with increased coating time and it was found that these alloys could serve as potential candidates for further in-vivo tests to establish their applicability
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Contreras, Vásquez Luis Felipe. "Mechanical synthesis of magnesium alloys for hydrogen storage." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8302/.
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In this work, synthesis, characterisation and hydrogen sorption properties of MgH2, Mg-Li alloy, NaMgH3, Li substitution in NaMgH3, Ca-Mg-H, and Li/Na substitution into Ca-Mg-H ternary systems have been investigated. Samples were ball milled under Ar or H2 for 2, 5, 10 or 15 h; then characterized by X-ray diffraction (XRD), Raman Spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis coupled with a mass spectrometer (TGA-MS). The compositional changes and reversibility were investigated using in-situ XRD. The X-ray intensities decreased with increasing milling, which corresponds to a reduction in crystallinity. For the first time, the effect of ball milling on the Raman of MgH2 was studied. For Mg-Li no formation of LiMgH3, Li2MgH4 was observed. NaMgH3 was synthesized after 2 h milling in Ar. DSC-TGA-MS showed H2 desorption occurs in 2 steps with a total mass loss of 5.9 wt. % H2 at 359 °C. Substituting Li in NaMgH3 led to a decrease in desorption temperature of about 50 °C when 0.5 mol (Li) was added. However, the total mass loss was decreased to 5.1 wt % H2. Ca-Mg-H and Li/Na substitutions into the ternary hydride showed desorption temperatures between 300 °C and 385°C with a maximum of 3.5 wt.% H2 released.
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Raghunathan, N. "Thermal and mechanical processing of aluminium magnesium alloys." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47726.
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Pouillier, Édouard. "Hydrogen-induced Intergranular Fracture of Aluminum-Magnesium Alloys." Paris, ENMP, 2011. http://www.theses.fr/2011ENMP0095.
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Les alliages d'aluminium de la famille 5XXX (Al-Mg) sont utilisés dans la fabrication de pièces de structure en raison de leurs bonnes propriétés mécaniques, de soudabilité et de résistance à la corrosion. Toutefois, dans des conditions d'utilisation sévères, une synergie entre la déformation plastique et les réactions de corrosion se produit et entraîne une fissuration intergranulaire, par corrosion sous contrainte (CSC), voire par fragilisation par l'hydrogène (FPH). La ductilité passe de 50% à quelques %, montrant une fissuration fragile. La compréhension des mécanismes qui régissent ce type de fissuration nécessite la détermination de l'importance respective des principaux facteurs (notamment mécaniques et chimiques). Cette étude se concentre sur le rôle de la plasticité cristalline dans le cas de la fragilisation par l'hydrogène. Pour ce faire, des éprouvettes préalablement fragilisées en surface par l'hydrogène (via un chargement cathodique) ont été sollicitées en traction. Ces essais ont été menés in situ dans le microscope électronique à balayage. Les résultats de corrélation d'image ont montré que les fissures s'amorcent dans des régions faiblement déformées adjacentes à des régions fortement déformées, là où les contraintes intergranulaires les plus élevées sont attendues. Par ailleurs, la cartographie des orientations cristallines des surfaces observées au cours des essais a servi de base à un maillage réaliste de la structure, qui a permis de calculer les champs de contraintes et de déformation locaux à l'aide d'un modèle de plasticité cristalline. Le modèle a été validé par la confrontation des prédictions à la mesure des champs de déformation et aux courbes de chargement macroscopique. Les contraintes ainsi estimées par simulation numérique ont permit d'établir un critère de rupture. Ce critère de rupture a ensuite été incorporé dans la simulation de microstructure quasi-2D grâce à un modèle de zone cohésive. Les résultats obtenus en accord avec les observations ont mis en avant la nécessité de développer une méthodologie permettant de prendre en compte les effets de la microstructure situés sous les surfaces étudiées. Ces microstructures ont été caractérisées à l'aide de plusieurs techniques d'analyse 3D de la morphologie microstructurale des agrégats polycristallins (EBSD par couches successives et par microtomographie rayons X des joints de grains à l'aide de diffusion de gallium). Les résultats des simulations avec les microstructures réelles en 3D dans le domaine élastique sont cohérant avec ceux obtenus en 2D pour des agrégats composés de 40 grains<br>Aluminium alloys that are strengthened by alloying elements in solid solution may present a particular sensitivity to intergranular stress corrosion cracking as a result of intergranular dissolution. In Al-5Mg alloys such as AA5083, precipitation of the β-phase (Al3Mg2) at grain boundaries strongly favours intergranular fracture. Previous experimental studies revealed that local plasticity seems to play a significant role in crack initiation. Nevertheless, the exact role of crystal plasticity in the vicinity of grain boundaries is not well understood. The main goal of this doctoral thesis is two-fold: (i) to study the role of the local stress and strain fields on the mechanism of intergranular stress corrosion cracking and, based on such understanding, (ii) to develop a micro-mechanics based model to predict the onset of grain boundary cracking, through a suitably defined failure criterion, and the subsequent intergranular crack propagation. An experimental procedure based on in-situ tensile tests within the chamber of an scanning electron microscope was developed to measure the evolution of local strain fields at various microstructural scales and of lattice orientation using digital image correlation and electron backscatter diffraction (EBSD) techniques, respectively. Digital image correlation techniques were used in particular over areas comprising just a few grains up to mesoscopic regions of the polycrystal to quantify the deformation and strain fields required in the multi-scale study of intergranular fracture. From these observations, it was established that interfaces between two grains which have undergone little amount of deformation but lying within a neighbourhood of significantly deformed grains are the first to develop micro-cracks. In addition, X-Ray tomography and serial EBSD sectioning analyses revealed that cracked grain boundaries were perpendicular to the applied tensile load, where maximum tensile tractions are expected. To determine the role of local stresses and local plasticity on the mechanisms of intergranular fracture, a dislocation mechanics based crystal plasticity model was employed to describe the constitutive behaviour of each grain in the finite element model of the in-situ experiments. The model parameters were calibrated as a function of the solid solution magnesium content in the aluminium alloy. Measured EBSD maps were relied upon to define the orientation of the discrete grain regions of the in-situ specimens in the corresponding multi-scale finite element (FE) models. From the FE results, a range of threshold values of the normal grain boundary tractions needed to initiate intergranular cracks was identified. This finding is in close agreement with the predictions from an analytical solution of a simplified model of intergranular cracking based on an extension of Eshelby's theory for inclusions. Finally, a cohesive zone model calibrated with the critical grain boundary tractions and typical surface energies was added to the FE model of the polycrystal. A comparison between the experimental and numerical results reveals a good agreement with the observed experimental cracking pattern
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Rocha, Patrick Thierry Almeida da. "Understanding corrosion mechanisms of novel biodegradable magnesium alloys." Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/21878.
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Mestrado em Engenharia de Materiais<br>A biodegradação de biomateriais em ordem a conseguir uma dissolução completa de um determinado equipamento após a realização do seu propósito, tem sido visto como uma ideia atrativa pela comunidade cientifica, devido ao elevado potencial nas melhorias a qualidade de vida do paciente e devido aos custos pós operatorios que podem ser melhorados.
O comportamento de biodegradação é consequência da elevada susceptibilidade à corrosão, inerente às ligas metálicas como o magnésio. Esta característica deve-se à instabilidade química causada pela inserção das ligas num ambiente agressivo às mesmas. Esta afirmação continua a ser verdadeira no caso em que ligas de mágnesio são introduzidas no corpo humano, em contacto com iões agressivos ao metal, presentes nos fluídos corporais.
O trabalho de investigação proposto nesta tese, tem como temática o estudo de mágnesio puro, ligas de Mg-XGd e Mg-XGd-YMn, onde o rácio estequiométrico dos elementos é X=2,5 e Y=1. As ligas usadas não se encontram comercializadas, mas existe um forte interesse no seu uso como material biodegradável devido às boas propriedades mecânicas apresentadas pelas mesmas. No entanto as taxas de corrosão necessitam de ser modeladas de forma a viabilizar o seu uso como biomaterial, e uma melhor compreensão sobre os mecanismos de corrosão podem ajudar no design de futuras ligas.
O foco deste trabalho consiste em desvendar a natureza da corrosão e devido a isso diversos fatores serão estudados, usando diferentes técnicas de caracterização i) Observar a microestrutura e os microconstituintes presentes, o seu tamanho, morfologia e composição elemental, usando para tais fins técnicas de MEV e EDS. A rugosidade e o potential Volta apresentada pelos diversos constituintes da microstrutura será levado a cabo por técnicas de MFA e SKFM.
ii) Técnicas eletroquímicas, como a eletroquímca de impedância e polarização dinâmica, serão usadas de forma a perceber o comportamento do sistemas em diversos meios eletrolíticos. Tempos longos de imersão foram realizados durante medições de Impedância eletroquímica.
iii) A composição quimica e o estudo de fases dos produtos de corrosão são realizados usando técnias de EDS e DRX, o que permite identificar os tipos de produtos preferencialmente formados durante o processo de corrosão.
iv) Uma série de outras técnicas proporcionaram uma informação mais consistente sobre o comportamento de corrosão nas ligas de mágnesio, como a evolução do hidrogénio e a observação das secções de corte.
A reproducibilidade foi estudada usando uma amostragem em diversas técnicas. Entretanto este trabalho é baseado numa comparação qualitativa que permite entender e desvendar o porquê, como e qual o tipo de corrosão que é apresentado pelos diversos sistemas em estudo.
Os resultados obtidos pelas diversas técnias revelaram que os fenómenos de corrosão são dependentes do tipo de ambiente e das suas condições. A presença de níveis de impurezas superiores aos limites de tolerância, como o ferro, mostram que a taxa de corrosão é aumentada na presença dos mesmos, visto que aumenta a actividade catódica dos intermetálicos. O manganês como elemento de liga reduz esse efeito, diminuindo a respetiva taxa de corrosão. A formação de produtos de corrosão é dependente do pH do meio, e assim, a precipitação de compostos vai diferir com o eletrólito em uso. O sistema ternário e o magnésio puro demonstraram taxas de corrosão aproximadamente de 0,18 mm/a a 330h de imersão, imerso na solução de PBS. Estas taxas de corrosão podem ser adequadas para aplicações biomédicas.<br>Biomaterials bring valuable improvements to the biomedical field. The idea behind the biodegradation behaviour of a biomaterial which can be used as an implant in the human body has attracted the attention of the scientific community, due to various benefits which may improve quality of life of injured humans.
The biodegradation behaviour of metals arises from the high susceptibility to corrosion of metallic alloys in the human body, which are in contact with aggressive ions presented by human body fluids. This especially concerns magnesium and its alloys. Magnesium alloys must comply with the requirements which are put on the biodegradable materials. Among such requirements one can name mechanical properties and controlled corrosion activity.
Investigation in this work performed on several Mg samples, including a pure magnesium (HP Mg), Mg-XGd and Mg-XGd-YMn systems with variation in stoichiometry ratio of elements, X=2 and 5 and Y=1. These are non-commercial Mg alloys which may present interest due to their potential as biodegradable materials. A tailoring of the corrosion rate is required to reduce the corrosion rate of such alloys. For that, it is incredibly wise to understand the corrosion mechanisms in different electrolytes and conditions.
To study the influence of factors which affects corrosion a series of characterization techniques were used. At first microstructure and microconstituents as intermetallics, their size, shape and elemental composition, were evaluated using SEM and EDS. Roughness and Volta potential of the different phases present in the microstructure were studied using AFM/SKFM technique, which allows to correlate the Volta potential with local corrosion of intermetallics and to observe dissolution and precipitation processes at the microscale.
Also, electrochemical measurements, such as Electrochemical Impedance Spectroscopy (EIS), potential dynamic polarization, were conducted accessing corrosion behaviour of systems in different electrolytes during short immersion times. For electrochemical characterization, in the extended time of immersion EIS was used. To obtain the corrosion rate, it was used the hydrogen evolution method.
Then corrosion products chemistry was studied using X-ray diffraction and energy dispersive spectroscopy techniques, which allow to identify the type of products formed in the different electrolytes and to correlate their formation with corrosion behaviour. Cross section analysis and identification of corrosion morphology were accessed on samples after EIS tests.
Reproducibly of measurements were ensured by studying a set of replica samples. This work is based on qualitative/qualitative comparison of results which allowed a better understanding why, how and which corrosion is present in the different systems.
The different techniques used revealed that corrosion is highly dependent on the environment and the conditions of measurements. The presence of high levels of impurities as iron induces high levels of corrosion by increasing the cathodic activity of intermetallic. Manganese as an alloying element reduces the effect of the impurities in corrosion. Corrosion products formation is pH dependent, and so, the precipitation of corrosion products compounds from different electrolytes may be beneficial or nonbeneficial to corrosion. The ternary system and the HP Magnesium demonstrate corrosion rates approximately 0.18 mm/year in PBS solution, which can be adequate for biomedical applications.
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Griffiths, David Glyndwr John. "Understanding texture weakening in magnesium rare earth alloys." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/understanding-texture-weakening-in-magnesium-rare-earth-alloys(3823f6a8-bba7-415f-9326-adc1b1655c8c).html.
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Magnesium has the lowest density of any structural metal making it a strong candidate for weight savings in the aerospace and automotive industries. However, strong crystallographic textures combine with anisotropic deformation modes to severely limit formability in wrought magnesium alloys. Recently improved formability has been achieved by the addition of small concentrations of solute rare earth elements which reduce the intensity of recrystallisation textures. Developing a mechanistic understanding of this effect is critical in leading alloy design towards a new class of highly formable wrought magnesium alloys. In this study the static recrystallisation mechanism of rolled magnesium rare earth alloys, which causes the texture weakening, is examined with a particular emphasis on the contrasting texture weakening effects in binary and tertiary magnesium rare earth alloys. In binary magnesium-rare earth alloys the `rare-earth' texture is simply a weakened deformation texture, while recrystallisation of magnesium-zinc-rare earth alloys produces unique `rare-earth' texture components. In the binary alloys weakened recrystallisation textures are attributed to the generation of `off-basal' orientations within regions of high strain localisation during deformation. These orientations recrystallise and subsequently dominate the recrystallised texture. Texture weakening by this mechanism is also thought to be observed in non-rare earth magnesium alloys where dynamic recrystallisation is suppressed by cold rolling. The unique rare-earth texture components in magnesium-zinc-rare earth alloys are found to be determined by the orientation of shear bands in the material. Similarly to texture weakening in the binary alloys, nuclei for these orientations are thought to develop during deformation as a result of strain incompatibilities within shear bands. The mechanism forming these orientations remains unclear, however it is postulated that a complex change in recovery behaviour within shear bands, as a result of rare earth and zinc additions, may be the cause. Retarded dynamic recrystallisation is suggested to be of critical importance in the texture weakening mechanisms of all magnesium alloys, both rare earth and non-rare earth. In rare earth alloys dynamic recrystallisation is suppressed by the segregation of rare earth atoms to grain boundaries. A combination of high resolution TEM and EDX shows rare earth atoms form clusters approximately 2nm in diameter on grain boundaries which are expected to retard dynamic recrystallisation through a solute drag mechanism.
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Harrison, Andrew William. "High strain rate superplasticity of aluminium-magnesium alloys." Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/7821.
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Barber, Lee P. "Characterization of the solidification behavior and resultant microstructures of magnesium-aluminum alloys." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-12234-112022/.
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Wiese, Björn Verfasser], and Rainer [Akademischer Betreuer] [Schmid-Fetzer. "The Effect of CaO on Magnesium and Magnesium Calcium Alloys / Björn Wiese ; Betreuer: Rainer Schmid-Fetzer." Clausthal-Zellerfeld : Technische Universität Clausthal, 2017. http://d-nb.info/1231364858/34.
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KUPFER, JOHN CARLTON. "A SEARCH FOR CHANGES IN THE BAND STRUCTURE OF EXTREMELY STRAIN-FREE MAGNESIUM-CADMIUM CRYSTALS AS A FUNCTION OF ALLOYING, IN THE DILUTE LIMIT (DE HAAS-VAN ALPHEN, FERMI SURFACE)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187953.
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We report here a study of a specific doublet of de Haas-van Alphen frequencies in pure Mg and very dilute Mg(Cd) alloys with the magnetic field aligned with the c-axis. The work involved three stages. First, the use of extremely strain-free crystals, temperatures down to 40 millidegree Kelvin, large amplitude modulation, and the fast Fourier transform allowed the components of this doublet to be well resolved. This resolution allowed measurement of the changes in the cross-sectional area as a function of magnetic field orientation to verify the assignment of this doublet to the cap and monster arm junction at the top of the Brillouin zone. Third, with the magnetic field aligned with the c-axis, the splitting of this doublet offered a direct and sensitive indication of any symmetry breaking changes in the 0001 Fourier component of the ionic lattice potential in Mg upon the introduction of Cd. C. B. Friedberg's analysis of his electron interference lineshape data from the quantum interferometer in Mg had indicated that the energy of this band gap should increase by 40% with the introduction of 15 ppm Cd. Our data indicate that any change in the energy of the band gap must be at least three orders of magnitude smaller than that indicated by Friedberg. Our data are, in fact, consistent with there being no changes in the electronic band structure or the Fermi surface of Mg(Cd) alloys (with up to 0.02% (At) Cd), from that of pure Mg.
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Zhang, Zhan. "Development of magnesium-based alloys for elevated temperature applications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0026/NQ52270.pdf.
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Williams, J. R. "Corrosion of aluminium-copper-magnesium metal matrix composites." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239852.
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Shang, Lihong. "Effect of microalloying on microstructure and hot working behavior for AZ31 based magnesium alloy." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115880.
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The formability of Mg alloy sheet in the as-hot rolled condition depends on the microstructure developed during hot rolling. In general, the formability of Mg alloys is improved by finer grain sizes. 'Microalloying' levels of calcium (Ca), strontium (Sr), and cerium (Ce) have been found to refine the as-cast structure, but there is no information as to whether this effect will be reflected in the as-hot worked structure and formability. Thus, in this work, the effects of microalloying levels of calcium (Ca), strontium (Sr), and cerium (Ce) on the microstructures (from as-cast to as-hot rolled) and subsequent hot deformation behavior of AZ31, nominally 3% Al, 1% Zn, and 0.3%Mn, were systematically investigated.<br>To include the effect of solidification rate these alloys were cast in different moulds (preheated steel mould, Cu-mould, and water cooled Cu-mould). One-hit compression testing at temperatures between 250°C ∼ 400 °C, strain rates of 0.001, 0.01, 0.1 s-1 and strains from 0.2 up to 1.0, was performed to investigate the basic hot compression behavior, while two-hit compression testing was conducted to determine the static softening behavior. Hot rolling of the microalloyed AZ31 alloys was then carried out to study the effects of microalloying on as-hot rolled structure under two sets of rolling schedules. To investigate the formability of these microalloyed sheets, tensile tests were completed over a temperature range between ambient and 450°C, at strain rates between 0.1 and 0.0003 s-1.<br>Results show that Ca and Sr act to refine the as cast grain size and the second phases, consistently promoting fine and uniform as-hot rolled grain structure. With regard to grain refinement, calcium has the strongest effect, whereas Ce is most effective for second phase refinement. In addition, microalloying retards grain growth during hot tensile testing. Multiple alloying presents a combined and complementary effect.<br>A refined and uniform grain structure combined with well dispersed and thermally stable second phases significantly improves the hot formability of AZ31 sheets by promoting dynamic recrystallization (DRX) in the matrix, resisting grain coarsening, and retarding the development of cavitation and necking. Under the superplastic condition of 450°C and 0.0003 s -1, the elongation was improved by 17% with Ca only, 26% with Ca and Ce, 51% with Ca and Sr, and 59% with Ca, Sr and Ce.
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Abu, Leil Tarek. "Development of new magnesium alloys for high temperature applications." Clausthal-Zellerfeld Universitätsbibliothek Clausthal, 2010. http://d-nb.info/1001190777/34.
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Abu-Farha, Fadi K. "INTEGRATED APPROACH TO THE SUPERPLASTIC FORMING OF MAGNESIUM ALLOYS." UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/493.
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The economical and environmental issues associated with fossil fuels have been urging the automotive industry to cut the fuel consumption and exhaust emission levels, mainly by reducing the weight of vehicles. However, customers increasing demands for safer, more powerful and luxurious vehicles have been adding more weight to the various categories of vehicles, even the smallest ones. Leading car manufacturers have shown that significant weight reduction, yet satisfying the growing demands of customers, would not be feasible without the extensive use of lightweight materials. Magnesium is the lightest constructional metal on earth, offering a great potential for weight-savings. However, magnesium and its alloys exhibit inferior ductility at low temperatures, limiting their practical sheet metal applications. Interestingly, some magnesium alloys exhibit superplastic behaviour at elevated temperatures; mirrored by the extraordinarily large ductility, surpassing that of conventional steels and aluminium alloys. Superplastic forming technique is the process used to form materials of such nature, having the ability to deliver highly-profiled, yet very uniform sheet-metal products, in one single stage. Despite the several attractions, the technique is not widely-used because of a number of issues and obstacles. This study aims at advancing the superplastic forming technique, and offering it as an efficient process for broader utilisation of magnesium alloys for sheet metal applications. The focus is primarily directed to the AZ31 magnesium alloy, since it is commercially available in sheet form, possesses good mechanical properties and high strength/weight ratio. A general multi-axial anisotropic microstructure-based constitutive model that describes the deformation behaviour during superplastic forming is first developed. To calibrate the model for the AZ31 magnesium alloy, systematic uniaxial and biaxial stretching tests are carried out over wide-ranging conditions, using 3 specially-designed fixtures. In a collaborative effort thereafter, the calibrated constitutive model is fed into a FE code in conjunction with a stability criterion, in order to accurately simulate, control and ultimately optimise the superplastic forming process. Special pneumatic bulge forming setup is used to validate some proposed optimisation schemes, by forming sheets into dies of various geometries. Finally, the materials post-superplastic-forming properties are investigated systematically, based on geometrical, mechanical and microstructural measures.
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Yuan, Yudie. "Localised corrosion and stress cracking of aluminium-magnesium alloys." Thesis, University of Birmingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433422.
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Yi, Xiaodong. "Rapidly solidified magnesium : nickel alloys as hydrogen storage materials." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5174/.
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Due to high hydrogen capacity, good reversibility and low cost, magnesium hydride is one of the most promising hydrogen storage materials. However, the high desorption temperature and slow hydriding kinetics hinder the application of magnesium hydrides. To improve the hydrogen storage characteristics of magnesium hydrides, many effective treatments have been developed and applied, such as ball milling, melt spinning, alloying with other metals, adding catalysts and using thin film technique. In this work, melt spinning and alloying with Ni were the main sample modification methods used to improve hydrogen storage properties for magnesium hydrides. At the beginning of this project, it was found that it was difficult to repeat the methodology of sample preparation in the literature. Therefore, sample synthesis method was developed after numerous preliminary trials and a series of Mg-Ni alloys were melt-spun successfully. The structural characterization and analysis of hydrogen storage property were performed on the melt-spun Mg-Ni samples in a range of compositions. It was found that a nanocrystalline / amorphous structure was produced by melt spinning, and a metastable intermediate phase, Mg\(_6\)Ni, was discovered in the melt-spun materials. The melt-spun Mg-Ni ribbons exhibited fast kinetics of both absorption and desorption at 300 °C, with a high capacity. Moreover, they exhibited low temperature and even room temperature hydrogen sorption, with slow kinetics.\(\gamma\)-MgH\(_2\) phase, which forms usually under high pressure, has been found in the samples, which probably caused the ambient hydrogen absorption.
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Narsimhan, Raghunathan. "Thermal and mechanical processing of commercial aluminium magnesium alloys." Thesis, Imperial College London, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395772.
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Reese, Gregory A. "Dissimilar Friction Stir Welding Between Magnesium and Aluminum Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955097/.
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Joining two dissimilar metals, specifically Mg and Al alloys, using conventional welding techniques is extraordinarily challenging. Even when these alloys are able to be joined, the weld is littered with defects such as cracks, cavities, and wormholes. The focus of this project was to use friction stir welding to create a defect-free joint between Al 2139 and Mg WE43. The stir tool used in this project, made of H13 tool steel, is of fixed design. The design included an 11 mm scrolled and concave shoulder in addition to a 6 mm length pin comprised of two tapering, threaded re-entrant flutes that promoted and amplified material flow. Upon completion of this project an improved experimental setup process was created as well as successful welds between the two alloys. These successful joints, albeit containing defects, lead to the conclusion that the tool used in project was ill fit to join the Al and Mg alloy plates. This was primarily due to its conical shaped pin instead of the more traditional cylindrical shaped pins. As a result of this aggressive pin design, there was a lack of heat generation towards the bottom of the pin even at higher (800-1000 rpm) rotation speeds. This lack of heat generation prohibited the material from reaching plastic deformation thus preventing the needed material flow to form the defect free joint.
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Rashed, Hossain Mohammad Mamun. "Composition and microstructure effects on superplasticity in magnesium alloys." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/composition-and-microstructure-effects-on-superplasticity-in-magnesium-alloys(ba55b973-c9fa-459b-a1e8-ff77017811b9).html.
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Magnesium is the lightest structural metal and magnesium alloys are therefore obvious candidates in weight critical applications. The environmental imperative to reduce vehicle emissions has recently led to intensified research interest in magnesium, since weight reduction is one of the most effective ways of improving fuel efficiency. The hexagonal close-packed structure of magnesium results in poor room temperature formability. However, on heating, several magnesium alloys show superplastic properties, with the ability to deform to very high strains (up to 3000%). This opens up the possibility of forming complex components directly by superplastic forming (SPF). As a result, SPF of magnesium is a highly active research topic. The most widely used class of magnesium alloys contain aluminium as the major alloying addition, which has a relatively high solubility in magnesium, and manganese, which has a less solubility. The effect of these elements on the deformation behaviour and failure mechanisms operating in the superplastic regime is not yet well understood. The objective of this work was to gain fundamental insights into the role of these elements. To do this, alloys with different aluminium content (AZ31 and AZ61) and manganese levels have been studied in-depth.After casting, all alloys were subject to a hot rolling procedure that produced a similar fine grain size and texture in each material. Hot uniaxial testing was performed at temperatures between 300 to 450 degC and at two strain rates to investigate the material flow behaviour, elongation to failure and failure mechanism. All of the alloys exhibited flow curves characterised by an initial hardening and extensive flow softening region. Dynamic recrystallization did not occur, and the flow softening was attributed to grain growth and cavity formation. Increasing the level of aluminium in solution was observed to increase the grain growth rate, and also reduce the strain rate sensitivity. The elongation to failure, however, depended strongly on the manganese level but not on the aluminium content. This attributed to the role of manganese in forming coarse particles that act as sites for cavitation.To study cavity formation and growth, and its effect on failure, a series of tests were conducted to different strain levels followed by investigation of cavitation in 3-dimensions using X-ray tomography. New methods were developed to quantify the correlation between cavities and coarse particles using X-ray tomography data and it was shown that over 90% of cavities are associated with particles. Cavity nucleation occurred continuously during straining, with progressively smaller particles forming cavities as strain increased. The mechanism of cavity formation and growth was identified, and it has been demonstrated that particle agglomerates are effective sites for cavity formation even when the individual particles in the agglomerates are below the critical size predicted by theory for cavity nucleation sites. These results suggest that to improve the ductility of magnesium alloys in the superplasticity regime, it is most critical to minimise the occurrence of particle agglomerates in the microstructure.