Orientador: Prof. Dr. Jorge Tomioka / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2014. / No contexto energético, as mudanças climáticas e as crescentes crises energéticas aumentaram as preocupações e as pesquisas na área de acumuladores de energia, visando alcançar melhorias no cenário energético e ambiental global. Ao mesmo tempo, a sociedade tornou-se dependente do consumo de energia elétrica, sendo que falhas no fornecimento não são permitidas. Portanto, observa-se a necessidade da energia ofertada ser de boa qualidade e, principalmente, não sofrer interrupções. Atrelado a esses fatores, a bateria de Magnésio ¿ Ar passou a ser considerada uma fonte promissora de energia elétrica, principalmente pela abundância de Magnésio (sétimo elemento mais presente no planeta), por não poluir o meio ambiente, ser barata e possuir energia especifica elevada. Essas características transformam esse acumulador em um potencial substituto para outras tecnologias. No entanto, a bateria demagnésio possui desvantagens que precisam ser vencidas por meio de pesquisas para alavancar o seu uso comercial massivo. Sob essa perspectiva, neste trabalho propõe-se o estudo da liga de magnésio AZ91 para aplicação em baterias de Magnésio ¿ Ar, por meio de ensaios de porosidade e de dureza, como também análise microestrutural e mensuração do potencial de circuito aberto e das curvas de polarização potenciodinâmica, utilizando-se uma célula eletroquímica de três eletrodos e um potenciostato em diferentes tempos de imersão da liga AZ91 na solução eletrolítica de NaCl 0,1 M. A porosidade da peça, observada no microscópio óptico com ampliação de 50 vezes, revelou que em cada fase de solidificação existem poros de tamanhos diferentes, com distribuição específica. Conforme o processo de resfriamento ocorre, nota-se a presença de poros maiores. Relacionado à porosidade, a dureza apresentou valores maiores na fase inicial de solidificação, onde a porosidade é menor. Por meio da análise microestrutural, foi possível verificar a presença de dendritas, com uma complexa dispersão de segunda fase na liga (alumínio), porosidades e inclusões. As medidas de potencial de circuito aberto indicam uma tendência de resistência à corrosão em temposmaiores de contato da amostra com a solução de NaCl. Não foi possível observar passivação aparente na amostra, nem pontos de corrosão localizada (pite) nas curvas de polarização potenciodinâmica. As variações no potencial de corrosão apontaram uma maior resistência à corrosão em tempos de imersão maiores; contudo, os valores estáveis de densidade de corrente de corrosão demonstram que a velocidade de corrosão permaneceu constante, sendo que a camada de óxido formada não contribuiu na proteção do material. Para a aplicação em baterias de magnésio, esses resultados conferem uma limitação da liga AZ91, pois a camada de óxido formada pode prejudicar o funcionamento do dispositivo em processos de descarga intermitente. As principais formas de controlar a eficiência da bateria de Magnésio ¿ Ar são por meio da composição da liga, da oxigenação, do pH, da temperatura e da concentração de sais NaCl no eletrólito. / In the energy sector, weather changes and rising energy crisis raised concerns and research in energy accumulators to achieve improvements in overall environmental and energy scenario. At the same time, society has become dependent on electricity consumption, so failures in supply are not tolerated. Therefore, the energy needs to have a good quality, and not suffer interruptions. Coupled to these factors, the battery Magnesium ¿ Air has been considered a promising source of electricity, mainly by the abundance of magnesium (seventh-most element present on the planet), not to pollute the environment, be cheap and have high specific energy. These characteristics transform this accumulator in a potential substitute for other technologies. However, the magnesium battery has disadvantages that need to be overcome through research to leverage their massive commercial use. From this point of view, this study proposes the characterization of magnesium alloy AZ91 for application in batteries Magnesium ¿ Air, testing the porosity and hardness, as well as microstructural analysis, and the measurement of the open potential circuit and the potentiodynamic polarization, in various immersion times using an electrochemical cell with three electrodes. The porosity of the part, observed in the optical microscope, revealed that at each stage of solidification, the pores have different sizes and distribution. As the cooling process occurs, could observe the presence of larger pores. Associated to the porosity, hardness values were higher in the initial phase of solidification, where the porosity was less. Through microstructural analysis was verified the presence of dendrites, with a complex dispersion of second phase in the alloy (aluminum), porosity and inclusions. The open potential circuit indicated a tendency for corrosion resistance in greater immersion time in the solution of NaCl. In all cases, the potentiodynamic polarization curves did not exhibit apparent passivity, or points of localized corrosion (pitting). The changes in corrosion potential showed greater resistance to corrosion in immersion times larger, however, the steady state values of corrosion current density demonstrated that the corrosion rate remained constant and the oxide layer formed did not protect the material. For use in magnesium batteries, these results provided a limitation of the AZ91 alloy, because the oxide layer can disturb the functioning of the device in cases of intermittent discharge. The main ways to control the battery efficiency Magnesium ¿ Air are through the alloy composition, oxygenation, pH, temperature and salt concentration of NaCl in the electrolyte.

L’alliage de magnésium AZ31 présente une très faible densité. Cette caractéristique en fait un matériau apprécié pour la conception de structures légères. La limitation principale de son utilisation industrielle est sa mauvaise formabilité et ce en raison de la texture cristallographique des tôles qui s’avère être peu adaptée aux procédés de mise en forme tel que l’emboutissage. Cette texture résultant du laminage initial, l’ambition de ce travail est de la modifier en utilisant la technique de laminage asymétrique et de mesurer l’impact de cette voie sur la formabilité de l’alliage. Il a été montré que l’asymétrie, produite par un différentiel de vitesses de rotation des cylindres du laminoir, induit systématiquement de fortes instabilités plastiques sous forme de bandes de cisaillement. Des techniques de cartographie sur microscope électronique en transmission (ACOM) et à balayage (EBSD) ainsi que des analyses de texture par DRX ont été utilisées pour analyser les mécanismes physiques concourant à l’émergence de cette instabilité. Il résulte de cette analyse que l’asymétrie du laminage provoque une forte activité du système de glissement basal que ne compense ni les autres systèmes ni le maclage. Ceci conduit à une localisation marquée de la déformation plastique et à la ruine du matériau. / The low density of the magnesium alloy AZ31 makes it valuable for low weight components. The main limitation for industrial applications is the poor formability of sheets during deep drawing type processing. This is linked to the fibre crystallographic texture resulting from rolling. The objective of the present work is to modify the sheet texture through asymmetrical rolling. It has appeared that the asymmetry promoted by monitoring the roll speeds separately induces plastic instabilities through shear banding. The physical mechanisms involved in the instability were analysed with the help of orientation imaging techniques on transmission electron (ACOM/TEM) and scanning electron (EBSD/SEM) microscopes as well as with X-ray measurements. It is concluded that the shear resulting from the asymmetry in roll speeds promotes a dramatic increase of basal slip that neither twinning nor the activities of other slip systems are able to compensate. Such activity induces strain localisation and premature failure of the material.

The submitted work is aimed at the unconventional fluoride conversation coating preparation on the AZ31, AZ61, ZE10 and ZE41 magnesium alloys by their immersion in Na[BF4] molten salt. The influence of the preparation parameters (such as temperature and time) on the quality of the fluoride conversion coating is investigated. Methods of light and scanning electron microscopy were used for the evaluation of morphology, chemical composition and thickness of the coating. Short and long-term corrosion tests were executed to analyze the corrosion performance in simulated body fluid solution at 37 ± 2 °C with and without the fluoride conversion coating. The short-term behavior was evaluated by potentiodynamic tests, namely by the linear polarization. Long-term performance was assessed by electrochemical impedance spectroscopy or immersion tests. The coating preparation parameters influence on the character of the formed fluoride conversion coating was defined based on the obtained results. The next part of the thesis deals with the description of the possible mechanism of formation and kinetics of growth of the unconventional fluoride conversion coating on the selected AZ61 magnesium alloy. In this part, further detailed analyses were carried out to investigate the microstructure and chemical composition of the fluoride conversion coating using focused ion beam, transmission electron microscopy and X-ray photoelectron spectroscopy.

Cílem této diplomové práce jse najít nejnižší možnou tloušťku nikl-fosforového povlaku, který může být galvanicky pokoven mědí bez defektů na horčíkové slitině, nikl-fosforového nebo měděného povlaku. V teoretické části jsou shrnuty poznatky o hořčíkových slitinách a jejich korozi. Navíc se teoreticá část zaměřuje na popis procesu bezproudého niklování a elektrochemického pokovování mědí a jejich porovnání. Na konci teoretické části je shrnut současný výzkum o elektrochemickém pokovování hořčíkových slitin. V experimentální části byl popsán proces přípravy povlaků Ni-P a Cu na horčíkové slitině AZ91. Na jedné vrstvě a dvojité vrstvě Ni-P povlaku byla provedena elektrodepozice mědi. Navíc byl diskutován vliv předůpravy před samotnou elektrodepozicí mědi. Za účelem zjištění korozních vlastností vzorků byl vykonán potenciodynamický test. Následně byly připraveny metalografické výbrusy jednotlivých vzorků a pomocí světelného a rastrovacího elektronového mikroskopu byla provedena charakterizace. Na konec bylo zjištěno prvkové složení jednotlivých povlaků pomocí EDX analýzy.

Nowadays, magnesium alloys are used in many sectors of human activity, particularly in the aerospace and automotive industries, due to a combination of good mechanical properties and low density of magnesium. Recently, however, the attention is paid to the possibility of using magnesium alloys in the medical field, mainly due to the chemical properties of magnesium. The diploma thesis is focused on evaluating of the corrosion behavior of AZ31alloy and AZ61 alloys in SBF solutions that are solutions simulating body fluids. The alloys were subjected to immersion test in Hank’s solutions for time span from 24 to 1008 hours. The corrosion process was evaluated based on several factors: alloy composition, time and pH changes. The thesis also describes in detail the methodology for establishing magnesium and zinc by method of flame absorption spektrometry (F AAS). The determination of aluminum was carried out by atomic absorption spectrometry with electrothermal atomization (ET AAS).

In this work have been identified mechanical and fatigue properties of magnesium alloy AZ31 with 0.5% calcium, which was cast using squeeze casting. In addition, it was observed microstructure of the alloys and made fractographic assessment of fracture surfaces after fatigue loading.

Microstructure and mechanical properties of AZ61 magnesium alloy in cast condition and after solution annealing were compared. The compare of mechanical properties of alloy, their hardness and microanalysis of occurring phases are included in this work. For compare has been used a light microscopy, tensile test, hardness measurements and scanning electron microscopy.

The aim of this diploma thesis was summary of all steps and knowledge necessary to deposition of quality Ni-P coatings deposited on wrought magnesium alloys AZ31 and AZ61. There is the treatise about wrought magnesium alloys AZ31 and AZ61. Thesis includes its phase composition in the theoretical part. There are given its possible processing methods too. Next, there is desribed the mechanism of deposition of Ni-P coatings, components required to electroless deposition and factors affecting the quality and properties of these coatings. The theoretical part is ended by serie of reviews. Authors of these reviews deal with pretreatment of substrates, preparation, characterization and measuring of mechanical, structure and corrosion properties of deposited coatings. The optimalization of pretreatment, parametres and composition of nickel bath suitable for magnesium alloys is described in experimental part. The microstructure, present interlayer between substrate and Ni-P coating and chemical composition of deposited coatings was observed and measured by optical and electron microscopy. The mechanical characterization of Ni-P coatings was performed by microhardness tester.

This thesis deals with mechanical and fatigue properties of magnesium alloy AZ91 processed by EX-ECAP method. This method involves the application of extrusion followed by equal-channel angular pressing. To obtain basic mechanical characteristics, the tensile test were carried out at room and elevated temperatures. Further the fatigue tests were performed and obtained data were used to compile S-N curve. The work also includes metallographics analysis of microstructure and fractographic analysis of fracture surfaces of tensile and fatigue test specimens.

in english For their positive influence on mechanical and physical properties of the material, methods of severe plastic deformation are popular for quite some time today. Rotary swaging is one of them. With its simplicity and productivity, it has the potential for industrial use. It is a radial swaging of rods or tubes, which results in decreasing of their diameter. Influence of this method is researched on extruded rods made of magnesium alloy AZ31. Experiments are made on five samples of different degree of swaging (different diameter). This allows to research gradual evolution of properties during the swaging. Results show significant positive influence on grain size (and microstructure in general) of originally extruded rod. During swaging there is an evolution of material texture and increase in strength.