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Electrochemical characteristics of AZ31 and AZ61 magnesium alloys in Hanks‘ solutions
Minda, Jozef ; Wasserbauer, Jaromír (referee) ; Tkacz, Jakub (advisor)
This thesis deals with the characterization of electrochemical corrosion properties of magnesium alloys as promising materials for biomedical applications. The wrought alloys AZ31 and AZ61 were used and exposed to corrosive environments of Hanks solutions (SBF) to simulate environmental conditions in living organisms. For the evaluation of the surfaces was used scanning electron microscopy (SEM) with elemental analysis measured by energy-dispersive spectroscopy (EDS). Short-term (5 min) and long-term (72 h) corrosion tests were conducted in order to optimize the measurement methodology and obtain corrosion parameters - especially corrosion potential (Ekor), corrosion current density (ikor) and polarisation resistance (RP). To evaluation of the short-term tests were by potentiodynamic tests, namely the linear polarization (LP) test. Long-term tests were measured by electrochemical impedance spectroscopy (EIS). Effects of the composition of the alloys (AZ31 and AZ61), surface treatment (grinding and polishing) and the composition of the solution (SBF without Ca, Mg, and with Ca, Mg) were compared. Complex corrosion behaviour in time was characterized and corrosion mechanisms were discussed.
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Conversion coatings and their characterisation
Březina, Matěj ; Doležal, Pavel (referee) ; Zmrzlý, Martin (advisor)
Aim of this study is to improve corrosion resistance of magnesium alloy AZ91 by conversion coatings. Influence of alloy microstructure on conversion coating growth and corrosion resistance was evaluated. Properties of pure magnesium and magnesium alloy AZ91 as well as the influence of alloying elements on properties of this alloy are described in theoretical part. Recent results of corrosion protection by conversion coatings on AZ type magnesium alloys are summarised in recherché part. Practical part focuses on preparation of hexavalent chromium based conversion coating and phosphate-permanganate based conversion coating on as cast AZ91 magnesium alloy, these coatings were subsequently applied on annealed AZ91 magnesium alloy. Corrosion protection of the coatings prepared on as cast and annealed alloy was evaluated by potentiodynamic measurements and testing in neutral salt spray. Furthermore the influence of plasma activation on phosphate-permanganate coating surface was studied.
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Reactivity and controll of properties of metallic materials
Tkacz, Jakub ; Šoukal, František (referee) ; Zmrzlý, Martin (advisor)
This thesis is focused on corrosion protection of magnesium alloys AZ 91. Very important is material corrosion in some environments and last but not least surface treatment as grinding, polishing and etching. Theoretical part of this thesis is about magnesium and magnesium alloy. It focuses on properties, in order to determine the best procedure for corrosion protection. It characterize material corrosion- for example corrosion in special environment (atmosphere, water, etc.) or elektrolyte corrosion. Big part of theoretical part is focused on electrochemistry, in particular kinetic aspects (Tafel diagrams, corrosion current, etc.) and potentiostatic testing, where are observed properties of material in relation to potential: corrosion potential Ecorr, brakedown potential Ebd and repassivation potential Erp. This work present preparing, utilization and positive or negative aspects of corrosion protection. Metallography is important too since metallographical preparation is crucial for the research on the material. Described metallography procedures are mounting, grinding, polishing, etching and interpretation. Experimental part of this thesis is in particular about corrosion properties of magnesium alloy AZ 91. It focuses on calculation of corrosion rate in defferent environments. Principle is mass defekt of the alloy. The environments are: destilled water, hot service water and 3% NaCl solution (like sea water). Last but not least are important. procedure manipulation with materials. Very important are choice and composition of solutions, etching time, choice of polishing cloth, lubricant solution and good pressure. Beacuse of this aspects can be show corrosion action of environments on magnesium alloy AZ 91 by photographies.
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Passivation of magnesium alloys
Krejčířová, Dana ; Sponar, Jan (referee) ; Zmrzlý, Martin (advisor)
Diploma thesis deals with the technology of surface modifications of magnesium alloys. Basic knowledge from the field of the corrosion of metal materials. The division corrosion according to way of attack and corrosion environment, etc. There is an enumeration of ways of the corrosion defence. Questions of surface modifications with an emphasis on passivation by conversion coating and its analysis. Characteristics of magnesium and its alloys. Magnesium alloys with lithium, possibilities of its passivation and the verification of corrosion resistance. Enumeration of the used devices, chemicals and materials. characteristics of the used alloys. creation of the corrosion resistance standard. Research in passivation on the alloy containing 12 percent of lithium. The verification of the corrosion test usability based on the suggestion of the background research results. The test results for passivated as well as untreated samples and the reference material (steel). Aplication of chromate-free passivation and corrosion test on the alloy containing 12 percent of lithium.
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Protection of magneisum alloys
Ruttkayová, Veronika ; Wasserbauer, Jaromír (referee) ; Zmrzlý, Martin (advisor)
The aim of this bachelor thesis is to characterize the mechanical properties of protective coatings on magnesium alloy AZ91. In the introductory there are summarized the findings of magnesium, magnesium alloys, corrosion and protection against it. Important properties such as adhesion and hardness were tested by standardized tests. The result can be used to determine application fields of these coated alloys in practice.
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Applications of magnesium alloys
Köhler, Tomáš ; Ročňáková, Ivana (referee) ; Němec, Karel (advisor)
This bachelor thesis includes basic knowledge of magnesium and its alloys. It also deals with their properties, division, and possibilities of heat treatment. The thesis then summarizes the application of magnesium alloys in individual branches of industries. With their usage for particular parts, a comparison with other construction materials, including the evaluation of using magnesium alloys and their advantages and disadvantages, is conducted.
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Corrosion protection of magnesium alloys
Minda, Jozef ; Ptáček, Petr (referee) ; Zmrzlý, Martin (advisor)
This work deals with an alternative procedure to conventional surface treatment of magnesium alloy AZ31 and AZ91 by fluoride coating layer. Synthesis of fluoride layers was carried out in the melt of NaBF4, while were following coating properties depending on the set process parameters, particularly temperature. The evaluation of coating were used scanning electron microscopy (SEM), light microscopy (LM) and immersion tests in 3.0% NaCl solution of 1, 8, 24, 48 h addition was carried out a short immersion test, in the strongly corrosive 70% HNO3. The coating was analyzed by energy dispersive spectroscopy (EDS or EDX) to determine the chemical composition. Tests showed very good corrosion resistance and showed that in this way, a reproducible compact coating was formed. The analysis identified a layer of stechiometric compounds MgF2 and NaMgF3. At the same time was the current research in the field of corrosion protection of Mg alloys. The prepared coating was confronted with current technology and in conjunction with searches were designed options such research can continue this kind of coating proceed.
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Magnesium alloys
Březina, Matěj ; Šoukal, František (referee) ; Zmrzlý, Martin (advisor)
The study is focused on corrosion and corrosion protection of magnesium and magnesium alloys. The theoretical part describes properties of magnesium and magnesium alloys. It shows their advantages as well as their disadvantages and discusses ideal use for these alloys. The theoretical part analyses basic corrosion characteristics and typical corrosion processes. It deals with types of corrosion protection and ways of its use. The experimental part was focused on metallographic analysis and corrosion behavior of magnesium alloy AZ91. Metallographic methods were used for preparing AZ91 to corrosion tests. The experimental part compared corrosion rate and degradation of pure AZ91 and AZ91 with conversion coating (phosphate-permanganate) in 3,5% sodium chloride solution in times: 1, 8 and 48 hours.
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Propsective surface treatments of magnesium alloys
Drábiková, Juliána ; Doležal, Pavel (referee) ; Zmrzlý, Martin (advisor)
The aim of this bachelor thesis is to summarize the methods of surface treatment of magnesium alloys and discussion of theireffectiveness of corrosion protection. In contrast to other metallic material used in technical practice, magnesium alloys have the lowest corrosion resistance, which can be increased by alloying or by use of surface treatments. The introduction part of the thesis deals with general knowledge about magnesium, its alloys AZ31, AZ91 and their corrosion processes. The recherché includes actual results of research about these alloys. Emphasizedare fluoride conversion coatings and composite coatings based on nickel, where their preparation is described and attention is focused on their properties in the sense of corrosion protection. Concluding the work, we give a critical assessment of the pros and cons of corrosion protective coatings on Mg alloys. Finally, there are suggested some convenient experiments to prove the repeatability of results published in the recherché literature.
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