A l'heure où les matériaux composites prennent une part toujours plus importante dans les structures aéronautiques, l'utilisation de l'alliage d'aluminium-lithium 2050 assemblé par Friction Stir Welding (FSW) est envisagé pour remplacer les structures rivetées en alliages d'aluminium traditionnels. L'objectif global de ce travail de thèse était d'étudier le comportement en corrosion et en corrosion sous contrainte de joints soudés FSW de l'alliage d'aluminium-lithium 2050 mais aussi l'influence d'un post-traitement thermique sur les comportements observés. Dans ce but, la microstructure, le comportement mécanique et le comportement en corrosion et en corrosion sous contrainte de l'alliage 2050 servant de matériau de base à l'élaboration des joints soudés FSW ont d'abord été analysés ; ensuite, nous nous sommes focalisés sur le comportement en corrosion et en corrosion sous contrainte des structures FSW proprement dites, en analysant bien entendu la microstructure complexe de ces joints soudés et les propriétés mécaniques résultantes. Les résultats obtenus montrent que l'alliage 2050, bien que sensible à certaines formes de corrosion, semble bien plus performant que les alliages d'aluminium traditionnellement utilisés en aéronautique. Sa sensibilité à la corrosion sous contrainte notamment est très faible. Les structures FSW, après traitement thermique post soudage, ont également un très bon comportement en corrosion et en corrosion sous contrainte. Les joints soudés FSW de l'alliage d'aluminium-lithium 2050 apparaissent donc comme une solution très prometteuse pour l'industrie aéronautique. / Today, composite materials are more and more used for aircraft structures; however, the aluminium-lithium 2050 alloy joined using a Friction Stir Welding (FSW) process could be used to replace riveted structures made of traditional aluminium alloys. The aim of this PhD work was to study the corrosion behaviour and stress corrosion cracking (SCC) behaviour of FSW joints of aluminium-lithium 2050 alloy and also the influence of a post welding heat treatment on the behaviours observed. Therefore, the microstructure, the mechanical behaviour and the corrosion and SCC behaviour of the 2050 alloy used for the FSW joints were first analyzed; then, the work was focused on the corrosion and SCC behaviours of the FSW joints. The complex microstructure of the FSW joints and the resultant mechanical properties were studied. The results showed that the 2050 alloy was more corrosion resistant than traditional aluminium alloys used for aircrafts even if it was susceptible to intergranular and/or intragranular corrosion. Its susceptibility to SCC was very low. The FSW joints, after a post welding heat treatment, also show a low susceptibility to corrosion and SCC. As a conclusion, the FSW joints of 2050 alloy seem to be a relevant solution to replace riveted structures of traditional aluminium alloys.

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In most of the tribological experiments studying friction and wear behaviour, the contact interface is hidden. The present work attempts to overcome this hidden-interface problem by carrying out real-time tribological experiments inside Transmission Electron Microscope (TEM). This is achieved by developing an in situ TEM triboprobe which can carry out nanoscale indentation, sliding and reciprocating tests on an electron transparent sample inside TEM. A novel in situ TEM triboprobe is developed by characterising the individual components involved in the development. Coarse positioning of a sharp probe is achieved using inertial sliders. Fine motion of the probe is controlled using a 4-quadrant tube piezoceramic. This triboprobe is capable of carrying out high stiffness tribological experiments inside TEM. The interface is viewed at high resolutions in real time during the experiments using a movie rate CCD camera. In indentation experiments a sharp probe is brought into contact with the sample surface. During indentation of Aluminium alloy tribolayer, it has been observed that the cracks originate from subsurface and propagate to the surface causing delamination-like material removal. Indentation experiments on protruding silicon particle in Aluminium-Silicon (Al-Si) alloy shows that initial deformation is elastic. Once the load is increased, the particle starts indenting the soft aluminum matrix, and results in sinking of the particle into the aluminium matrix. Once the particle starts sinking, the increase in the displacement causes the generation of a crack and the propagation of this crack results in the fracture of the particle. The sliding experiments inside TEM allowed the direct visualization of asperity level interaction during sliding. The preliminary experimental results of nanoscale sliding experiments carried out using an AFM tip as the sample. The adhesive instability is observed as snap-in and snap-out events. The snap-out distance seems to depend on the local geometry of the contact. To simulate reciprocating wear, a sharp diamond probe is brought into contact with Al-Si alloy and reciprocated sinusoidally at 0.5Hz. At lower loads no wear is observed. However, when the normal load is increased, material starts getting removed in thin slivers, and most of the wear debris generated get swept away from the track. Some wear debris get entrapped in between the sliding surfaces; subsequently they join to form larger wear particles. The trapped particles generated during the test act like rollers and a significant increase in the stroke-length is observed accompanying the rolling action of the particle. The phenomena like agglomeration and dissociation of the wear particles has also been observed. Repeated deformation of the trapped particles leads to the formation of tiny liquid drop on some of the wear debris. The liquid consists of gallium which comes from the sample preparation technique. The interaction between the liquid droplets has been studied by carrying out liquid-bridge pulling experiments. Liquid gallium gets cooled with time during tensile pulling of the droplets. A nano-filament is formed between the droplets during pulling. After some time, the droplet gets solidified and coalescence of droplets does not take place. Further frictional heating was necessary to form the bridge again. The in situ TEM triboprobe, which allow the tribological processes to be observed dynamically under high resolutions, is a power full tool in detecting fundamental tribological interactions.

The microstructures of the near-surface layers on AA3104 aluminium alloys and their evolution through rolling and deep drawing processes have been investigated. The effect of the near-surface layers on the optical property of AA3104 aluminium alloy has also been assessed. It was revealed that two types of near-surface deformed layers, both with different microstructures different from the underlying bulk alloy, were generated on the surface of AA3104 aluminium alloy during rolling. Both of them are characterized by ultrafine, equiaxed grains, with diameters <100 nm for type A near-surface deformed layer and <200 nm for type B near-surface deformed layer. A high population density of nano-sized, oxygen-rich particles is present along grain boundaries within type A deformed layer. But type B deformed layer is free of oxygen-rich particles. Type A deformed layer was generated through two mechanisms, i.e. geometric dynamic recrystallization and mechanical alloying. Rolling introduced plastic strain in the surface/near-surface region of aluminium sheet was of sufficient magnitude to cause geometric dynamic recrystallization and thus microstructure refinement. In addition, the incorporation of oxides into the near-surface region was also involved in the formation of type A deformed layer. However, the formation of type B deformed layer was only attributed to severe strain induced geometric dynamic recrystallization. Type A deformed layer was mainly formed at the early stages of hot rolling. The subsequent rolling and deep drawing reduced the thickness of type A deformed layer by distributing it over a larger surface area. During cold rolling, type A deformed layer broke into patches with the extension of alloy surface. Type B deformed layer may be generated on the nascent surface if the strain is sufficiently severe to cause geometric dynamic recrystallization. For the hot rolled alloy sheets, the surface/near-surface region is mainly covered by type A deformed layer. However, for the alloys after cold rolling, only limited area is covered with type A deformed layer. The thicknesses of the near-surface deformed layers are not uniform across the surface of AA3104 aluminium alloy. The maximum thickness of type A deformed layer on transfer slab is approximately 4 µm, while that on re-roll gauge sheet is ~1 µm, and ~0.8 µm on the final gauge sheet, ~400 nm on formed cup and ~100 nm on formed can. Type A deformed layer is randomly distributed as patches on the cold rolled aluminium sheet. The reflectivity of oxygen-rich particles is lower compared with the reflectivity of aluminium. As a result, the type A deformed layer patches absorb more incident light than the area without type A deformed layer. Further, there are plenty of micro-scale mini-cracks present on type A deformed layer, their opening sizes are in the equivalent scale of the wavelength of visible light. The incident light may not able to be reflected out if they go into these mini-cracks. It is more prone to happen for short wavelength light since it is easier for them to go into the mini-cracks than long wavelength light. As a result, less short wavelength visible light is reflected from the type A deformed layer patches. Thus, such patches exhibit a yellow appearance while the surrounding area appears the original silver white aluminium appearance. The aluminium sheet with a high coverage of type A deformed layer exhibits a low total reflectance. Further, its total reflectance is with a significant “red shift”. Neither the macro-scale surface roughness nor the ultrafine grain size affects the total reflectance of aluminium alloys. The total reflectance of aluminium alloys is primarily dependent on the presence of type A deformed layer.

The diploma thesis Technology of CNC production of aluminium alloy part is based on the particular specification of the company FP cz s.r.o. The core of the work lies in the proposal of production technology of the given part made from aluminium alloy which is machined by two universal CNC lathes with operating system FANUC. There is an introduction to the issue of characteristics and machinability of aluminium and its alloys because of coherence of the thesis. Practical part is focusing on the particular proposal of production technology which consists of the casting analysis, method of clamping on the chosen machines, choice of tools and verification of the production. There can be achieved effective production and significant time reduction with proposed technology.

This diploma thesis deals with finding and verification of appropriate technological parameters of SLM technology for the processing of aluminum alloy 2618. In the theoretical part, an introduction to additive manufacturing of aluminum alloys and general description of processes occurring during SLM production is given. Based on general knowledge were designed different types of testing samples produced by sintering the metallurgical powder using 400 W ytterbium fiber laser, which so far in the literature for aluminum alloy 2618 were not described. As the result, the technological parameters dependence on relative density and the detailed overview of the 2618 alloy processing by SLM technology is determined.

Here we present the development of an aluminium alloy based hydrogen storage tank, charged with Ti-doped sodium aluminium hexahydride Na3AlH6. This hydride has a theoretical hydrogen storage capacity of 3 mass-% and can be operated at lower pressure compared to sodium alanate NaAlH4. The tank was made of aluminium alloy EN AW 6082 T6. The heat transfer was realised through an oil flow in a bayonet heat exchanger, manufactured by extrusion moulding from aluminium alloy EN AW 6060 T6. Na3AlH6 is prepared from 4 mol-% TiCl3 doped sodium aluminium tetrahydride NaAlH4 by addition of two moles of sodium hydride NaH in ball milling process. The hydrogen storage tank was filled with 213 g of doped Na3AlH6 in dehydrogenated state. Maximum of 3.6 g (1.7 mass-% of the hydride mass) of hydrogen was released from the hydride at approximately 450 K and the same hydrogen mass was consumed at 2.5 MPa hydrogenation pressure. 45 cycle tests (rehydrogenation and dehydrogenation) were carried out without any failure of the tank or its components. Operation of the tank under real conditions indicated the possibility for applications with stationary HT-PEM fuel cell systems.

Combinations of different materials are increasingly used in the modern engineering structures. The driving forces of this trend are rising fuel costs, global warming, customer demands and strict emission standards. Engineers and industries are forced to improve fuel economy and cut emissions by introducing newly design engines and lightweighting of structural components. The use of lightweight materials in the structures has proved successful to solve these problems in many industries especially automobile and aerospace. However, industry still lacks knowledge how to manufacture components from polymeric materials in combination with metals where significant differences exist in properties. This thesis aims to demonstrate and generate the methodology and guidelines for hybrid joining of aluminium alloys to thermoplastics using friction stir welding. The developed technique was identified, optimized and evaluated from experimental data, metallography and mechanical characterization. The success of the technique is assessed by benchmarking with recent literatures. In this work, lap joints between aluminium alloys (AA5754, AA6111) and thermoplastics (PP, PPS) were produced by the friction stir welding technique. The specimens were joined with the friction stir welding tools under as-received conditions. Metallic chips were generated and merged with the molten thermoplastic to form a joint under the influence of the rotating and translating tool. The effects of process parameters such as rotational speed, translational speed and distance to backing were analyzed and discussed. The investigation found joint strength was dominated by mechanical interlocking between the stir zone and the aluminium sheet. The results also show that the joint strength is of the same order of magnitude as for other alternative joining techniques in the literature. / <p>QC 20150908</p>

The master’s thesis deals with high strength aluminium alloys AlZn4Mg (EN AW 7020). This alloy is used for high strength, low density, a good corrosion resistant and a good weldability in protective atmospheres. At first this thesis is described to aluminium alloys, ways of manufacturing and history. Next this thesis mainly deals with wrought aluminium alloys, heat treatment this alloys and alloys Al-Zn-Mg. Tensile tests were made of alloys EN AW 7020 at room temperature and increased temperature. Next this alloy was made of fatigue test and metallographic analysis. The model was construct. This model describe to behaviour alloy at increased temperature and this model was compared with measure values. This thesis describe to behaviour of study alloy at room temperature and increased temperature.

Yes / In this study, a new double pin tool was utilized for the development of AA6061/316 stainless steel reinforced composite by employing the friction stir processing technique for the first time. The microstructure, hardness, tensile, tribological, and corrosion behaviors of the fabricated composites were investigated and comparative assessments were made with the results obtained from the single-pin tool. The results showed that particle-matrix reaction did not occur in the composites irrespective of the nature of the tool profile. The double-pin tool outstandingly boosted the grain refinement (7.01–5.78 μm), particle fragmentation, and distribution within the Al matrix due to the additional pin-assisted plastic deformation, high straining, dynamic recrystallization, and Zener pinning effects. The double-pin tool improved the microhardness (127–141 HV), tensile strength (162–233 MPa), and corrosion resistance of the composite with respect to the single-pin tool counterparts. The replacement of the single pin tool with a double pin tool diminished the specific wear rate (0.38–0.22 mm3/Nm) of the composite. The double-pin tool has a favourable impact on the structure, mechanical, and corrosion behaviours of the AA6061/316 stainless steel reinforced composite. It is thus recommended for composite development.