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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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An Acoustic Emission Study of Deformation Mechanisms in Novel Magnesium Alloys at Uniaxial and Low Cyclic Loading
Horváth, Klaudia ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
This work is focused on the study of the relationship between microstructure and deformation mechanisms in magnesium (Mg) alloys during uniaxial (tension, compression) and low cyclic loading by the acoustic emission (AE) technique. The main attention is paid to the study of tension-compression yield asymmetry and twinning-detwinning process during changes in deformation mode in novel aluminium-free Mg alloys, where the deformation texture influences the activation of various deformation mechanisms. The results contribute to the understanding of dislocation processes and twin activation (especially of twinning-detwinning process) during cyclic loading. These processes are of great importance because they influence significantly the fatigue life of Mg alloys.
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Investigation of collective behaviour of lattice defects by the acoustic emission technique
Molnárová, Orsolya ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
The Portevin-Le Chatelier effect is a macroscopic, spatio-temporal instability of plastic deformation. This phenomenon appears in some industrially important metallic alloys, e.g. based on iron, aluminum or magnesium if these materials are deformed at suitable temperature and strain rate. The effect is manifested as stress fluctuations (serrations) on deformation curves, which corresponds to macroscopic and localized events of plastic deformation in the material. It demonstrates a nonlinear cooperative motion of dislocations (line defects of the microstructure) during plastic deformation. Study of nonlinear aspects of dislocation dynamics is of great importance for understanding the patterns of plastic deformation. It also brings a considerable application potential for the design of novel structural materials. By the collective motion of dislocations the stress fields of the structural defects interact and release mechanical energy in form of elastic waves. These waves can easily be detected by the acoustic emission technique.
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Dependence of mechanical properties of polycrystalline magnesium on microstructural parameters
Čapek, Jan ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
The deformation of commercially pure magnesium with various grain size in different temperatures is investigated in the present work. Compression and tensile test were done on three different samples in temperature range of 20řC-300řC. Samples are deformed at strain rate of 1,8 mm/min. Simultaneously, the acoustic emission is recorded. The microstructure of the deformed material is also studied by means of optical microscopy. We focus on twinning activity at various temperatures and asymmetry between tensile and compression deformation.
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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 properties of magnesium alloy AZ31 after corrosion degradation
Horynová, Miroslava ; Lukáč, Pavel (referee) ; Doležal, Pavel (advisor)
The present study is focussed on assessment of cyclic deformation response and fatigue behaviour of bare and precorroded AZ31 magnesium alloys. Corrosion degradation was carried out in a salt spray fog (5% solution of sodium chloride) for 480 and 1000 hrs. Microstructure, mechanical properties, low- and high-cycle fatigue behaviour of experimental material in as-cast condition has been evaluated. Furthermore, the corrosion behaviour of material has been investigated. The fatigue tests have been performed using precorroded specimens to assess influence of corrosion degradation on cyclic deformation response and on low- and high-cycle fatigue behaviour. Influence of local corrosion degradation on initiation of fatigue cracks has been studied.
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