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Study of mechanical and thermal properties of nanoparticle-reinforced composites
Németh, Gergely ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
Title: Study of mechanical and thermal properties of composites reinforced by nanoparticles Author: Gergely Németh Department: Department of Physics of Materials Supervisor: RNDr. Kristián Máthis, Ph.D. Abstract: In the present work the deformation behavior of magnesium-based alloy AZ31 reinforced by SiC nanoparticles which was produced by horizontal continual casting is studied. Tension tests in the room temperature, compression tests in the temperature range of 20řC-300řC have been preformed. Samples was with two different orientation. Deformation strain rate was 10-3 s-1 . Simultaneously, the acoustic emission is recorded and studied. The mechanisms of plastic deformation of material are discussed mainly in term of mechanical twinning. Dependence of deformation behavior in compression on temperature is analyzed. The microstructure of original and deformed material is also studied. Keywords: magnesium alloys, composit material, mechanical twinning, metals with hexagonal structures.
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Mechanical properties of ultrafine-grained magnesium alloys
Nováková, Helena ; Stráská, Jitka (advisor) ; Král, Robert (referee)
This work is focused on the mechanical properties of ultrafine-grained magnesium alloy AZ31 prepared by EX-ECAP method. The main goal of the bachelor thesis is to find external conditions of superplastic deformation: deformation temperature (measured in the range 150 řC - 350 řC) and strain rate (measured in the range 10-5 s-1 - 10-2 s-1 ). Properties related to the mechanisms of superplasticity (strain rate sensitivity parameter, maximum stress and maximum elongation) were evaluated. Deformation mechanisms were furthermore observed using atomic force microscopy.
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Study of thermal stability of Mg-alloys strengthened by quasicrystalline phase
Vlasák, Tomáš ; Čížek, Jakub (advisor) ; Procházka, Ivan (referee)
This bachelor thesis deals with thermal stability of icosahedral phase in Mg-Zn-Y alloys. To study this phenomenon, samples of Mg-3.5Y-35Zn alloy were prepared and equal channel angular pressing method (ECAP) performed at two different temperatures was used to refine their microstructure. Phases in the samples were characterised by scanning electron microscopy and energy-dispersive X- ray spectroscopy. Strengthening effect of icosahedral phase (I-phase) with quasicrystalline structure was examined by measuring Vickers hardness of the samples. Temperatures at which precipitation and dissolution of various phases occur were studied by differential scanning calorimetry. Finally, defect recovery with increasing temperature was investigated by means of positron annihilation lifetime measurement. To identify chemical elements surrounding dislocations coincidence measurements of Doppler broadening of annihilation peak were conducted. Obtained results are as follows. Icosahedral dendritic structures are stable in Mg-3.5Y-35Zn alloy at temperatures up to 350 řC, at higher temperatures they are dissolved in the matrix. Recovery of dislocations takes place in the temperature range from 140 řC to 260 řC and leads to decrease in strength of the alloy processed by ECAP. Concentrations of zinc and yttrium are not enhanced...
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Influence of Solid Solution Elements and Precipitate Formation on the Mechanical Behaviour of Magnesium Alloys
Illková, Kseniya ; Chmelík, František (advisor) ; Karlík, Miroslav (referee) ; Landa, Michal (referee)
Title: Influence of Solid Solution Elements and Precipitate Formation on the Mechanical Behaviour of Magnesium Alloys Author: Mgr. Kseniya ILLKOVÁ Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc.RNDr.František Chmelík, CSc. Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Mg-1 wt. % Mn alloys containing about 1 wt.% of calcium (MX10), aluminium (AM11), cerium(ME11), yttrium (MW11), neodymium (MN11) and 8 wt.% of aluminium (AM81) were indirectly extruded with two different speeds. The partially recrystallised microstructures obtained in MX10, AM11, ME11 and MW11 after slow extrusion exhibited bimodal grain size distributions. Only in the case of AM81 and MN11 a fully recrystallised microstructure was found, indicating differences in the grain nucleation rate during recrystallisation. In these alloys, the weakest texture and, correspondingly, the lowest asymmetry in mechanical properties were also observed. The acoustic emission technique was used to reveal dislocation or twin controlled deformation in differently textured fractions of the microstructure during tensile and compression testing. A direct correlation between the acoustic...
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The numerical analysis of interactions between twins and precipitates in magnesium alloys
Bogdan, Miloš ; Gröger, Roman (referee) ; Šiška, Filip (advisor)
Hlavním cílem této práce je analýza napěťových polí, indukovaných dvojčatěním ovlivněných přítomností precipitátu před čelem dvojčete. Zvolený případ popisuje tahové dvojče {1012} 101 1 s lamelarními precipitáty v hořčíkové slitině AZ31. Systém je modelován metodou konečnýh prvků jako 2D elastická eliptická inkluze, se dvěmi elastickými precipitáty tyčovitého tvaru, nacházející se před čelem elipsy obklopené plastickou matricí modelovanou pomocí krystalové plasticity. Analýza dvojčat a precipitátů s různou tlouštkou ukazje inhibující účinek precipitátů na růst tloušťky dvojčat. Velikost tohoto účinku se mění s tloušťkou dvojčete v důsledku komplexní interakce mezi dvojčetem precipitátem a indukovanou plastickou zónou.
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Positron annihilation study of precipitation effects in Mg-Tb alloy
Hruška, Petr ; Čížek, Jakub (advisor) ; Vlach, Martin (referee)
Magnesium alloys are currently widely used in industry as a modern material. Magnesium based alloys with rare earth elements shows very promising mechanical properties. In the present work the precipitation effects and the deve- lopment of microstructure of the Mg13Tb alloy (containing 13 wt.% of terbium) during isochronal annealing were studied by positron annihilation spectroscopy, microhardness measurement and differential scanning calorimetry. According to the results the creation of the precipitates β′′ , β′ and β in the studied alloy was observed and activation energies of these precipitates were determined by the Kissinger method. By microhardness measurement the natural ageing at room temperature of the Mg13Tb alloy was observed and described. 1
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Evaluation of electrochemical characteristics of AZ61 magnesium alloy processed by squeeze casting
Pikner, Jan ; Hadzima, Branislav (referee) ; Fintová, Stanislava (advisor)
Bachelor thesis deals with the characterization of electrochemical corrosion properties of AZ61 magnesium alloy prepared by squeeze casting method. The theoretical part of the work focuses on properties of AZ61 alloy, influence of alloying elements on magnesium alloys and corrosion. The practical part of the work deals with electrochemical characteristics of AZ61 alloy with different surface condition in of 0.1 M NaCl solution. Corrosion potential (Ekor) and corrosion current density (ikor) were determined by potentiodynamic test. Polarisation resistance was determined by electrochemical impedance spectroscopy. Based on the measured results was discussed the influence of production, chemical composition, structure and surface treatment (grinding and polishing) on corrosion characteristics of the alloy.
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Preparation and evaluation of fluoride conversion coating created on AZ31 wrought magnesium alloy
Matějka, Lukáš ; Wasserbauer, Jaromír (referee) ; Fintová, Stanislava (advisor)
The aim of this work is optimization of preparation parameters of fluoride conversion coating on the wrought magnesium alloy AZ31 in Na[BF4] melt. The monitored factors for determining quality of the prepared coatings are homogeneity of the coating surface on ground and polished samples of magnesium alloy, mechanical properties of the coating (adhesion and hardness) and the coating thickness. The main parameter was the change in these properties at different exposition times of the material to the salt melt. Coating surfaces were documented on an inverted light microscope with the addition of images representative samples using SEM. The coating thickness was documented with inverted light microscope using a polarization filter. The chemical composition was determined on three representative samples using an energy-dispersive X-ray spectrometer. The mechanical properties of the coatings were determined by scratch test on REVETEST Scratch Testing System with detector of acoustic emissions. The resulting scratches were documented on a light microscope. It was proved that polished samples exhibit superior coating in respect with ground samples, wherein the coating did not fill the trench after the finish treatment (grinding). Constant chemical composition has been demonstrated in all the coatings. Polished sample after 2 hours of exposure in the Na [BF 4] melt exhibits best mechanical properties. The obtained data are of practical importance in the use of the alloy AZ31 in various fields of industry, medicine and other research.
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Fatigue behaviour of AZ31 and AZ61 magnesium alloys after corrosion degradation
Horynová, Miroslava ; Vojtěch, Dalibor (referee) ; Obrtlík, Karel (referee) ; Podrábský, Tomáš (advisor)
Dissertation thesis is focused on evaluation of influence of exposure in 5% salt fog on fatigue behavior of AZ31 and AZ61 magnesium alloy fabricated by squeeze casting method. Microstructure and mechanical properties of experimental materials have been evaluated. The AZ61 alloy was solution heat treated after prior optimization of the heat treatment process based on microstructural characteristics and mechanical properties. Depths of corrosion damage, corrosion rate and mechanism of corrosion of all three experimental alloys have been evaluated. Influence of prior corrosion exposure for 480 and 1000 hours on fatigue behavior of experimental materials was evaluated. Obtained data were compared with data obtained using smooth test specimens. Fractographic analysis was carried out on both smooth and precorroded specimens. Furthermore, influence of aluminium on corrosion and fatigue behavior of tested alloys was defined.
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Corrosion Resistance of Structural Magnesium Alloys
Tkacz, Jakub ; Pacal, Bohumil (referee) ; Hadzima, Branislav (referee) ; Havlica, Jaromír (advisor)
This thesis describes magnesium alloys, their properties and methods of their production. However, experimental part is focused on AZ91 magnesium alloy. Conversion coatings were prepared on the AZ91 surface – chromate coating, phosphate permanganate coating and fluoride coating. Corrosion resistance of the prepared coatings were compared by immersion tests and by potentiodynamic methods. Evaluation of corrosion resistance by immersion tests was successful only for phosphate permanganate coating. Only this coating was removed during cleaning of the samples. For comparison of corrosion resistance was important to find the correct procedures and optimize the measurements methods. For these purposes have been chosen galvanic zinc coating on steel sheets. Thickness of the zinc coating were 8 and 30 microns. This coatings provide uniform zinc surface without heterogenities which was important for the potentiodynamic measurements. After optimization methods for potentiodynamic measurements by galvanic zinc coatings have been measured magnesium alloy AZ91 uncoated and coated by conversion coatings. For uncoated AZ91 magnesium alloy was determined suitable method so called virgin cathodic curve. On the other hand, for the coated AZ91 magnesium alloys was determined suitable method so called combined curve, within which we measured cyclic voltammetry curve (± 5 mV) and then virgin anodic curve.
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