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Evaluation of corrosion properties of biodegradable ZE41 magnesium alloy
Honč, Jiří ; Minda, Jozef (referee) ; Tkacz, Jakub (advisor)
This thesis deals with evaluation of corrosion properties of biodegradable magnesium alloy ZE41. Corrosion characteristics of ZE41 wrought magnesium alloy specimens with polished and grinded surface were examined by electrochemical methods. 0,1M NaCl solution was used as corrosive environment. 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 characterized by scanning electron microscope (SEM) with energy-dispersive spectroscopy (EDS). Based on the results, the influence of phase composition and surface treatment on corrosion characteristics was discussed.
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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) ; Málek, Jaroslav (referee) ; Novák, Pavel (referee)
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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Vliv příměsových prvků a textury na plastickou deformaci protlačovaných hořčíkových slitin
Horváth, Klaudia ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
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. Keywords: Mg alloys, deformation tests, acoustic emission, texture
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Study of mechanical properties of magnesium-based composites
Farkas, Gergely ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
In the present work, the mechanical properties of AJ51 magnesium alloy and composite is studied. Compression tests in the temperature range of 20řC-300řC have been preformed. The microstructure of the specimen was studied by means of light optical microscopy. The work is focused on the elucidation of the micromechanisms acting during plastic deformation of the composite specimens. Further a comparison between the mechanical properties of alloy and the composite is presented.
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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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Mechanical properties of magnesium alloy AZ91E prepared by ECAP method
Darida, Jiří ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
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.
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Ni-P based coatings preparation on wrought magnesium alloys
Buchtík, Martin ; Fintová, Stanislava (referee) ; Wasserbauer, Jaromír (advisor)
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.
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Fatigue Behaviour of AZ31 and AZ61 Magnesium Alloys
Gejdoš, Pavel ; Lukáč, Pavel (referee) ; Kohout, Jan (referee) ; Podrábský, Tomáš (advisor)
This doctoral thesis deals with the fatigue behaviour of AZ31 and AZ61 magnesium alloy casted by advanced methods of casting squeeze casting. Based on the regression functions and measured fatigue data were determined fatigue characteristics of these alloys. The work also extends into the area of fatigue cracks in the AZ31 alloy. Were measured fatigue crack propagation rate on modified cylindrical specimens. The paper also outlines the possibilities for describing the fatigue behaviour of AZ61 alloy in extremely low-cycle fatigue.
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FATIGUE CHARACTERISTICS OF MODIFIED MAGNESIUM ALLOYS AFTER CORROSION DEGRADATION
Němcová, Aneta ; Očenášek, Vladivoj (referee) ; Hadzima, Branislav (referee) ; Pacal, Bohumil (advisor)
This doctoral thesis deals with the determination of the influence of plasma electrolytic oxidation (PEO) on fatigue behaviour of extruded AZ61 magnesium alloy in air and in the 3.5% NaCl solution. The coatings were formed in the silicate-phosphate electrolyte under pulsed current conditions at a frequency of 50 Hz. The influence of current density on coating formation was examined under current densities of 70, 130 and 200 mA cm-2 for different durations up to a maximum of 1800 s. 8 g dm-3 of KF were added to the electrolyte to study the influence of fluoride ions in plasma electrolytic oxidation. It is shown that fluoride ions inhibit localised oxidation in the initial stage of the process, associated with the secondary particles based on Al–Mn. The presence of fluoride also modified the sparking characteristics, decreased the rate of coating growth and changed the morphologies of the coatings. The influence of fluoride on the coating hardness, and the corrosion resistance of the alloy during exposure to salt spray, was negligible. Based on previous optimised PEO conditions, coatings formed under a current density of 130 mA cm-2 for 300 s in the electrolyte containing KF were chosen for fatigue testing. The high-cycle fatigue tests were carried out on cylindrical samples under a force controlled sinusoidal tension-tension cycle with asymmetry parameter R=0. The experimental data were fitted with Kohout & Věchet function. The fatigue limit of uncoated alloy in air for 107 cycles was determined at 145.4 MPa and the combination of PEO coating with chloride ions caused a reduction of ~55 %. Attention was paid to the fatigue crack initiation in different conditions of cyclic loading. The fracture surfaces underwent detailed fractography analysis including secondary crack observation on the gauge length. The contribution of Al–Mn particles were confirmed on the uncoated alloy in air and the presence of chloride ions were observed as another influential contributor to local corrosion attack. The cyclic loading caused spalling of the outer layer, and the multiple initiation was observed on PEO coated alloy, caused by cracks in the coating and stress transferring to the alloy.
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