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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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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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Studium nestabilní plastické deformace metodou akustické emise
Molnárová, Orsolya ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
The influence of the strain rate and heat treatment on the occurrence of plastic instabilities in extruded AlSi1MgMn (6082) and cold rolled AlMg4.5Mn0.4 (5182) alloys was studied. The samples were uniaxially loaded at various strain rates and at room temperature (RT). The results are discussed using concurrent acoustic emission (AE) monitoring during mechanical testing and the AE parameters are correlated to the microstructure and to the stress-time curves. All samples exhibited the Portevin-Le Châtelier (PLC) effect of different types, dependently on the heat treatment and the applied strain rate. The occurrence of the PLC effect is manifested by burst AE signals with high amplitudes. Statistical analysis of the AE signals has shown the power-law probability distribution.
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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 pre-compressed Mg-Zn-Ca alloy
Hegedüs, Marius ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
In wrought Mg alloys, their hexagonal closed packed structure together with a pronounced basal texture lead to anisotropy of mechanical properties. This bachelor thesis is focused on understanding the influence of previous deformation with further relaxation and/or additional heat treatment on deformation behaviour of the extruded Mg-Zn-Ca alloy. The significant influence of twins formed after pre-compression on mechanical properties was investigated. Evolution of microstructure, especially a formation of twins, is observed by light and scanning electron microscopy. The acoustic emission technique is used to determine active deformation mechanisms: dislocation slip and twinning. The results can be used for developing Mg alloys with enhanced properties.
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Investigation of deformation mechanisms in textured magnesium alloy
Dittrich, Jan ; Minárik, Peter (advisor) ; Lukáč, Pavel (referee)
Název práce: Studium deformačních mechanism· v hořčíkové slitině s texturou Autor: Jan Dittrich Katedra: Katedra fyziky materiál· Vedoucí bakalářské práce: RNDr. Peter Minárik, PhD., Katedra fyziky materiál· Abstrakt: Předložená práce se zabývá studiem deformačních mechanism·, zá- visejících na orientaci vzork· v·či p·vodní textuře válcované hořčíkové slitiny, pomocí pokročilých in-situ i ex-situ metod. Během deformačních zkoušek, které byly prováděny v tlaku a v tahu, byla současně zaznamenávána akustická emise. Mikrostruktura deformovaných vzork· poté byla zkoumána metodami optické mi- kroskopie a difrakce zpětně odražených elektron·. V práci byla zjištěna výrazná závislost mechanických vlastností a aktivovaných deformačních mechanism· na orientaci vzork· v·či zjištěné bazální textuře válcovaného plechu hořčíkové sli- tiny AZ31. Dále byla ustanovena souvislost mezi základními parametry akus- tické emise a aktivovanými deformačními mechanismy. Rovněž byla pozorována a objasněna asymetrická odezva akustické emise při deformaci tlakem a tahem, související s rozdílným vývojem mechanického dvojčatění v pr·běhu plastické deformace. Klíčová slova: hořčíkové slitiny, deformace, dvojčatění, akustická emise, EBSD
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