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Effect of alloying elements and texture on plastic deformation of extruded magnesium alloys
Horváth, Klaudia ; Dobroň, Patrik (advisor)
This work is focused on the study of the relationship between microstructure, texture and deformation mechanisms in aluminum-free magnesium (Mg) alloys. Extruded alloys containing zirconium, zinc, manganese and neodymium (ZK10, MN11, ZN11) in a form of rectangular profiles were deformed at room temperature. Uniaxial tensile and compression tests were performed in the extrusion (ED), transversal (TD) and normal direction (ND). The concurrent acoustic emission (AE) measurement was used in order to study the collective dislocation dynamic and the nucleation of twins. The deformation texture was studied by X-ray diffraction on samples deformed in compression up to different stress levels.
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Microstructure and mechanical properties of lightweight structural AZ31 alloy prepared by twin-roll casting method.
Zimina, Mariia ; Cieslar, Miroslav (advisor)
Title: Microstructure and mechanical properties of lightweight structural AZ31 alloy prepared by twin-roll casting method Author: Mariia Zimina Abstract: Microstructure of AZ31 twin-roll cast magnesium alloy was studied using light optical, electron and atomic force microscopy. The effect of annealing temperature on the microstructure was tested. Mechanical properties of a thin magnesium strip were investigated by means of microhardness tests and tensile tests at a relatively low strain rate 10-3 s-1 . Results show that the ductility of the twin roll cast strip increases with increasing deformation temperature, however, a remarkable decrease was observed at about 200 řC. This effect appears also in a conventionally cast ingot of a master alloy and is caused by a change of a deformation mode occurring at this temperature. Moreover, the effect of severe plastic deformation on the microstructure and mechanical properties was studied. Equal channel angular pressing was applied on magnesium strip samples and lead to a significant grain refinement accompanied by an unfavorable strengthening of the initial basal texture, which is effectively suppressed by a subsequent annealing. A constrained groove pressing was for the first time successfully applied on AZ31 twin-roll cast strip leading to an increase of...
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Investigation of dislocation structure evolution in advanced magnesium alloys
Šimko, Pavol ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
: This thesis deals with evolution of dislocation structures in mag- nesium alloys containing long-period stacking ordered phase (LPSO). Before de- formation the samples were studied by optical light microscopy, in the process of deformation by neutron diffraction. Obtained diffraction profiles were of two types, axial and radial diffraction profiles (created by planes oriented in the di- rection of deformation and orthogonally to the direction of deformation). Profiles were evaluated by Convolutional Multiple Whole Profile method and by Hexbur- ger program. This work is focused on the role of LPSO phase in the evolution of dislocation density and population of dislocations in slip systems depending on the composition of alloys and on the volume fraction of LPSO phase. 1
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Preparation and Characterization of Advanced Thermally-sprayed Coatings on Magnesium Alloys
Buchtík, Martin ; Hadzima, Branislav (referee) ; Fintová, Stanislava (referee) ; Ptáček, Petr (advisor)
The proposed dissertation thesis deals with the characterization of HVOF and APS-thermally sprayed coatings prepared on the AZ31 and AZ91 magnesium substrates. The theoretical part of the thesis describes in-detail Mg substrates used in the experimental part of the thesis. There are also characterized materials and coatings based on NiCrAlY and FeCrNiMoSiC metals, WC-CoCr cermets, and YSZ ceramic materials. At the end of the theoretical part, the literary research summarizing the characterization and analysis performed on thermally sprayed coatings on Mg alloys. Based on the theoretical knowledge, the characterization of Mg substrates and deposited coatings was performed in terms of the surface morphology, microstructure, and the chemical composition using the light microscopy (LM) and scanning electron microscopy with energy-dispersive spectroscopy (SEM+EDS). The phase composition of the coatings was analyzed using the X-ray diffraction (XRD). The diffractions corresponding to the sprayed coatings were compared with the feedstock powders, i.e. materials used for the spraying of the coatings. The characterization of the prepared coatings in terms of the mechanical and tribological properties was performed. The hardness and microhardness of the coatings as well as the coefficient of friction, and the wear rate were measured. The last chapter of the experimental part deals with the evaluation of the electrochemical corrosion properties by the potentiodynamic measurements in a 3.5% NaCl solution. In the case of exposed samples, the evaluation of the surface and coating/substrate interface was performed using LM and SEM with EDS. The mechanism of the corrosion attack and degradation was determined from the acquired knowledge and base on the results of the short-term measurements. Based on the measured results, it can be stated that the deposited coatings were successfully applied on the surface of both Mg alloys. All the coatings increase the surface hardness of the Mg alloys and significantly improve their tribological properties. However, except for FeCrNiMoSiC coatings, the corrosion properties of Mg alloys deteriorate due to the fact that the corrosion environment can pass through the coating to the less noble Mg substrate and the corrosion microcells are created.
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Magnesium castings and their applications
Škriečková, Natália ; Kaňa, Václav (referee) ; Pernica, Vítězslav (advisor)
This bachelor thesis is focused on summarizing the knowledge about magnesium and magnesium alloys and their use in various industries. In the introductory part, the beneficial properties of this metal, its alloys and methods of production are highlighted. The second part is focused on castings of these alloys, where we describe their preparation and the actual casting process in various ways. Based on previous research, we evaluate the development of the use of these alloys in various industries such as automotive, aerospace and electrical engineering, as well as modern use in medicine. Last but not least, we criticize the positives and negatives of the entire process of production of final parts in terms of environmental impact.
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Investigation of deformation mechanisms in Mg-Gd alloys
Szabóová, Andrea ; Mathis, Kristián (advisor) ; Drozdenko, Daria (referee)
Title: Investigation of deformation mechanisms in Mg-Gd alloys Author: Andrea Szabóová Department: Department of Physics of Materials Supervisor: doc. RNDr. Kristián Mathis, DrSc. Abstract: In the present work, the deformation behavior of magnesium-gadolinium binary alloys was investigated. Dependence on the concentration of Gd and deformation temperatures was studied. Extruded samples had relatively strong initial texture. Compression tests were done at room temperature and 200řC. Simultaneously with deformation acoustic emission was recorded. Data from acoustic emission was analyzed with advanced statistical methods. Results of the combination of these two experimental methods indicated that at the beginning of the deformation twinning is the dominant mechanism. In the following stage of plastic deformation non-basal slip systems became the governing deformation mechanism. With higher content of Gd the size of twins decreases as a result of the decreased mobility of twin boundaries caused by solute atoms. At higher temperatures twinning activity was increasing. In addition, results were confirmed by optical light and scanning electron microscopy. Keywords: magnesium alloy, deformation tests, acoustic emission, microscopy
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Galvanic plating of magnesium alloy with Ni-P bond coat
Zahálka, Martin ; Kosár, Petr (referee) ; Wasserbauer, Jaromír (advisor)
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.
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Evaluation of corrosion properties of biodegradable ZE41 magnesium alloy in simulated body fluid
Handlíř, Tadeáš ; Minda, Jozef (referee) ; Tkacz, Jakub (advisor)
The bachelor thesis is focused on the evaluation of the effect of processing of biodegradable magnesium alloy ZE41 on its corrosion properties. The corrosion properties of ZE41 wrought magnesium alloy specimens with polished and ground surface were evaluated based on the results of the electrochemical characteristics that took place in the simulated body fluid. Short-term tests were performed using linear polarization method, by which the corrosion potential, corrosion current density and corrosion rate was determined. Long-term evolution of corrosion behavior in terms of polarization resistance was studied by electrochemical impedance spectroscopy (EIS) during 168 hours. Also, the corrosion products were studied by scanning electron microscope (SEM). Based on the results, the influence of surface treatment and phase composition on corrosion characteristics was evaluated.
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Preparation and Characterization of Fluoride Conversion Coatings on Biodegradable Magnesium Alloys
Drábiková, Juliána ; Hadzima, Branislav (referee) ; Brezinová,, Janette (referee) ; Ptáček, Petr (advisor)
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.
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Study of the microstructure of deposited Ni-P coatings with different phosphorus contents
Najser, Tomáš ; Kosár, Petr (referee) ; Wasserbauer, Jaromír (advisor)
The aim of this bachelor thesis was the preparation and characterization of Ni-P coatings with different phosphorus contents on the substrate of AZ91 magnesium alloy. The theoretical part deals with magnesium alloys and specifies the utilized substrate AZ91. It also focuses on Ni-P coatings, their microstructure and their properties. However, there are also described factors affecting the rate of deposition and the resulting behavior of these coatings. Last but not least, the theoretical part summarizes the basic principles of laboratory methods used in the experimental part for observation and characterization of samples. Conclusion of the theoretical part consists of several background researches where the authors deal with similar problems and factors influencing the resulting behavior of Ni-P coatings. The experimental part is focused on the deposition of each Ni-P coatings on the AZ91 alloy and their characterization. The study of deposited Ni-P layers was focused on the determination of their microstructural texture by XRD method, mechanical properties and elemental composition depending on phosphorus content.
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