8 results
Now showing1 - 8 of 8
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Korrosionssimulation von pressgehärteten Stählen und Filiformfäden auf Aluminium(2021); A simulation model for the prediction of corrosion damage on coated press-hardened steel and aluminium, which may be parts of the automobile body, is developed. The properties of the metallic alloys and coatings are measured with metallographic and electrochemical methods (polarization curves, galvanostatic dissolution, impedance spectroscopy). A new approach to model the influence of corrosion products on the corrosion rate is presented.Publicationtype: Doctoral Thesis382 1630 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Numerische Simulation von Korrosionsprozessen für die industrielle Anwendung(2017-06); Das Ziel, Korrosionsschäden effizient und langfristig zu verhindern, verfolgt aktuell eine Vielzahl von Ingenieuren und Wissenschaftlern in Unternehmen und Forschungsinstituten. Da die Korrosion an sich allerdings eine Folge des Strebens aller Metalle in den energieärmsten Zustand überzugehen und von daher unvermeidlich ist, kann sie nicht endgültig gestoppt werden. Es ist jedoch möglich, den Korrosionsprozess durch gezielte Maßnahmen zu verlangsamen und auf diese Weise die praktischen Auswirkungen zu minimieren. Dies führt zu der Notwendigkeit die Funktionsweise des Korrosionsschutzes laufend zu überprüfen und für zusätzliche Rahmenbedingungen, wie neue Materialzusammensetzungen und Belastungssituationen, weitere spezifische Maßnahmen zu entwickeln. Dementsprechend müssen kontinuierlich industrielle Prototypen experimentellen Korrosionstests unterzogen werden, wodurch diese Prototypen unweigerlich zerstört werden. Dieses Vorgehen ist folglich sowohl kosten- als auch zeitintensiv und steht Entwicklungsingenieuren nur sehr begrenzt zur Verfügung. Die auf mathematischer Modellierung basierende Korrosionssimulation verbreitet sich somit in wachsendem Ausmaß als das Mittel der Wahl um Korrosionsprozesse zu verstehen. Bisher gibt es jedoch noch kein Softwaretool mit dem der Korrosionsprozess für industrielle Anwendungen ausreichend simuliert werden kann, da die verschiedenen Modellierungsansätze den notwendigen Anforderungen derzeit nicht gerecht werden. Entweder wird nur eine statische Betrachtung des Korrosionsrisikos berechnet, bei dem der zeitliche Korrosionsverlauf vernachlässigt wird, oder es wird die zeitliche Entwicklung verschiedenster Parameter über eine kurze Dauer an kleinen Testgeometrien dargestellt. Vor allem die Verformung der Geometrie durch den Korrosionsfortschritt über lange Zeitskalen stellt eine große Herausforderung dar, die noch nicht zufriedenstellend gelöst ist. Es ist dafür notwendig, die Bewegung der korrosiv angegriffenen Oberflächen gemäß des Materialabtrags zu beschreiben. Den vielversprechendsten Ansatz stellt die Arbitrary-Lagrangian-Eulerian-Methode dar, die jedoch im Rahmen dieser Arbeit sehr sensibel eingesetzt werden muss.Publicationtype: Doctoral Thesis926 2026 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The role of intermetallic phases in the corrosion of magnesium-rare earth alloysThe role of intermetallic phases in the corrosion of Mg-RE alloys A new concept to develop a RE based Mg alloy with improved corrosion resistance was followed in the current work. Based on subsequent characterisation steps to eliminate less suitable RE elements the best microstructure for improved corrosion resistance was identified. At first, the corrosion properties of selected RE elements were determined. Based on these results RE elements that have a potential to enhance the corrosion resistance of Mg-RE alloys were selected. Two aspects of RE elements were important for the selection: the electrochemical properties and the solid solubility in Mg. If the solubility limit of RE elements in the Mg matrix is exceeded, they form intermetallic phases with Mg. By performing galvanic coupling measurements the compatibility between Mg matrix and intermetallic phases were estimated. At that point three binary Mg-RE alloys systems remained (Mg-Ce, Mg-La, and Mg-Gd). To evaluate the influence of composition (amount of intermetallic phases) on the corrosion behaviour, four concentrations were cast with 1, 5, 10 and 15 wt. % of RE. Ce and La have a lower solid solubility in Mg matrix generating higher volume fraction of the secondary phases, thus higher dissolution rates in the binary Mg-RE alloys. While Gd with higher solid solubility shows a different behaviour. Additions of up to 10 wt. % Gd resulted in similar behaviour compared to 1 wt. % Gd addition. The most promising results were obtained for the Mg-Gd system with 10 wt. % Gd. Thus, the microstructure of this alloy was further modified by heat treatments to understand the influence of microstructural changes on corrosion behaviour. A ternary element was used to attempt further optimisation of the corrosion performance. Additions of Al, Zn, Ga and Y did not show any improvement in the corrosion resistance of Mg10Gd. This is due to increasing volume fractions of critical more noble phases and the microstructure dominated by eutectic phase formation. Thus galvanic effects became much stronger due to the increased amount of cathodic phases in the eutectic regions. Mn was the only suitable ternary alloying element as it did not lead to the formation of Mn-rich intermetallics. It was found in solid solution in the intermetallics and to a lesser extent in the matrix without modifying the microstructure but increasing the corrosion resistance. The results of this work allow the design of new corrosion resistant Mg-Gd-Mn alloys by electrochemical evaluation and understanding of the basic corrosion mechanisms and interactions of the different phases. Better performance was predicted for reduced Gd contents and was finally experimentally verified.Publicationtype: Doctoral Thesis720 3505 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Antibacterial Mg-Ag biodegradable alloys(2013); The use of magnesium alloys as degradable metals for biomedical applications is topic of ongoing research. As a further aspect, the demand for multifunctional materials is increasing. Hence, binary Mg-Ag alloys were designed to combine the favourable properties of magnesium with the wellknown antibacterial property of silver. In this study, three Mg-Ag alloys, Mg2Ag, Mg4Ag and Mg6Ag which contain 1.87%, 3.82% and 6.00% silver by weight respectively were casted and processed with solution and aging heat treatment. Afterwards, the samples were investigated in vitro for metallographic, mechanical, corrosive, cytocompatible and antibacterial properties. The metallurgical analysis and phase identification showed that all alloys contained Mg4Ag as the dominant second phase. The mechanical properties of the Mg-Ag alloys were dramatically improved in several parameters especially after heat treatment. Corrosion tests revealed that after heat treatment, content of silver reduced the corrosion rate and exhibited less susceptibility to pitting corrosion than pure magnesium. Mg(OH)2 and MgO presented as main magnesium corrosion products while AgCl was found as the primary silver corrosion product. Immersion tests demonstrated that content of silver did not significantly shift the pH, osmolality and magnesium ion release in the environment. Cultivation and cytotoxicity tests with both primary cells and cell lines revealed that Mg-Ag alloys induce no negative effect on cells and show minor cytotoxicity. Antibacterial testing in a dynamic bioreactor system proved the alloys to reduce the viability of two common pathogenic bacteria, Staphylococcus aureus and Staphylococcus epidermidis. In summary, biodegradable Mg-Ag alloys are cytocompatible biomaterials with adjustable mechanical and corrosion properties while having sound antibacterial ability.Publicationtype: Doctoral Thesis1012 2525 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of the microstructure on the creep behaviour of semi-solid processed magnesium-zinc alloysThe creep properties of two magnesium-zinc alloys, designated as MEZ (Mg-2.6wt%RE-0.4Zn-0.13Mn-0.12Zr) and ZECa (Mg-2.8Zn-1.9Ca-0.32RE-0.08Sr), have been studied in the thixocast state at temperatures of 135 to 200°C. The two alloys showed less creep than the state of the art AE42 alloy after 100 h of creep exposure up to 175°C and 80 MPa. The improvement on the creep resistance has been related to the bimodal microstructure obtained after thixocasting and to the quality of the castings.Publicationtype: Doctoral Thesis599 888 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Einfluss von keramischen Partikeln auf die Texturausbildung von Magnesiumknetlegierungen(2013); The influence of ceramic particles on texture formation during hot rolling of magnesium wrought alloys has been investigated. The starting material for deformation has been produced by casting. For this purpose basic experiments concerning the fabrication of particle modified alloys in gravity die casting were necessary. Agglomeration of particles proved to be a central problem. AZ31 based alloys have been selected for an application oriented rolling procedure. The desired weakening of the texture of the sheet material could not be accomplished. This is because the deformation degree obtained in the passes of a conventional nonisothermal rolling process is too low to activate mechanisms like particle stimulated nucleation. Furthermore the content and morphology of the ceramic particles could be identified as critical parameters for texture weakening. The findings of this work expand the state of knowledge concerning the influence of particles on recrystallization of magnesium wrought alloys and allows for a more purposeful development of alloys with improved texture formation.Publicationtype: Doctoral Thesis729 882 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Bolt Load Retention Response and Creep of AS41 Mg-Alloy(2010); This work studies the creep and bolt load retention (BLR) response of permanent mould AS41 Mg-alloy. Results show that fastener clamp load loss of AS41 is due to creep of the alloy at bolted joint during service. Creep of AS41 Mg-alloy is dominated by grain boundary sliding and dislocation climb depending on the stress and temperature under consideration. Pore development around solute segregated regions was found to influence creep deformation. BLR of AS41 was successfully modelled using compliance-creep relationship and FEA approach.Publicationtype: Doctoral Thesis1762 1621 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Vergleichende Untersuchungen zum Zug- und Druckkriechverhalten der verstärkten und unverstärkten Magnesiumlegierung AE42(2006); Minimum creep rates obtained from tensile and compressive creep test performed with the creep resistant magnesium die cast alloy AE42 and the AE42-based composite reinforced with 20 vol.-% Saffil fibers show an anisotropy in their stress dependence. Calculation of stress exponents and activation energies from dependence on applied stress and temperature gave indication of deformation mechanisms which occur during creep. A mathematic formalism connecting the creep rates between tensile and compressive creep on the one hand and between the two materials in the same mode on the other hand was developed.Publicationtype: Doctoral Thesis549 2131