No description available.

A redução de peso é uma questão tecnológica fundamental para a indústria aeroespacial, uma vez que diminui o consumo de combustível, resultando em redução de custos e contribuindo para a redução da emissão de gases de efeito estufa. Devido à relação favorável entre resistência mecânica e peso, as ligas de alumínio de elevada resistência mecânica contribuem favoravelmente para este aspecto. Entretanto, como estas ligas são dificilmente soldáveis pelos processos tradicionais envolvendo fusão, o procedimento de junção utilizado em aeronaves é a rebitagem, resultando em ganho de peso. O processo de soldagem por fricção (friction stir welding -FSW), desenvolvido no início dos anos noventa pelo The Welding Institute (TWI) do Reino Unido, se constituiu em um grande avanço para a soldagem das ligas de alumínio utilizadas na indústria aeroespacial, pois permite a produção de soldas mais confiáveis e virtualmente livres de defeitos. Entretanto, o aquecimento das peças e a deformação mecânica durante a FSW geram zonas com diferentes características microestruturais que, de acordo com a literatura, apresentam resistências à corrosão diferentes. Por oferecerem elevada resolução lateral, as técnicas eletroquímicas locais são úteis para elucidar as diferenças de reatividade local de eletrodos heterogêneos, como no caso de metais soldados. No presente trabalho técnicas eletroquímicas locais foram empregadas para caracterização da resistência à corrosão em meio contendo cloreto das diferentes zonas geradas pela soldagem de topo da liga de alumínio 2024-T3 por FSW, comparando-a com a exibida pelo metal base. O estudo foi complementado com a caracterização microestrutural destas regiões e também por ensaios macroscópicos de corrosão. Os resultados dos procedimentos de caracterização microestrutural confirmaram que a FSW provoca modificações na microestrutura das regiões afetadas pelo processo, principalmente no que concerne à distribuição das nanopartículas precipitadas durante o envelhecimento natural da liga. Por sua vez, os resultados dos ensaios macroscópicos de corrosão e eletroquímicos locais mostraram-se concordantes na determinação da região mais sensível à corrosão, que foi verificada como sendo as zonas termicamente afetada (Heat Affected Zone - HAZ) e termomecanicamente afetada (Thermomechanically Affected Zone - TMAZ) do lado do avanço da ferramenta de soldagem, mostrando também que as regiões afetadas pelo processo de soldagem apresentam resistência à corrosão inferior à do metal base. Através do uso da espectroscopia de impedância eletroquímica local (Local Electrochemical Impedance Spectroscopy - LEIS) foi evidenciado que o acoplamento galvânico entre as diferentes zonas geradas durante o processo de soldagem não desempenha um papel relevante na aceleração do processo corrosivo, o que está em desacordo com os resultados publicados em diversos estudos realizados com esta liga soldada por FSW. O trabalho apresenta ainda uma contribuição teórica original demonstrando que medidas de ângulo de contato e de espectroscopia de impedância eletroquímica em uma gota séssil podem ser usadas simultaneamente para a determinação da capacitância da dupla camada elétrica. As previsões do modelo teórico foram confirmadas tanto através de resultados obtidos com um sistema modelo como também em determinações realizadas nas diferentes regiões geradas pela soldagem por FSW da liga 2024-T3. / Weight reduction is a fundamental technological issue for the aerospace industry, as it decreases the fuel consumption, resulting in reduced both costs and greenhouse gases emission. Due to the favorable relation between strength and weight, high strength aluminum alloys favorably contribute to this aspect, but they remain difficult to weld by conventional processes involving fusion, and, therefore, the junction procedure used in aircraft is riveting, resulting in weight gain. The friction stir welding (FSW) process, developed in the early nineties by the \"The Welding Institute\" (TWI), United Kingdom, is a major breakthrough for the welding of aluminum alloys as it allows the production of more reliable and virtually defect-free welds. However, the heating of the parts and the mechanical deformation during FSW generate zones with different microstructures with different corrosion resistances. As they offer high lateral resolution, local electrochemical techniques are useful for elucidating differences in local reactivity of heterogeneous electrodes, as the case of welded metals. In the present work, local electrochemical techniques were employed to characterize the corrosion resistance in chloride environment of the different zones generated by butt welding the 2024-T3 aluminum alloy by FSW, and to compare this response with that displayed by the base metal. The study was complemented with the microstructural characterization of these regions and also by macroscopic corrosion tests. The results of the microstructural characterization confirmed that FSW causes changes in the microstructure of the regions affected by the process, especially with regard to the distribution of the precipitated nanoparticles during the natural aging of the alloy. The results of the macroscopic corrosion and of the local electrochemical tests showed good agreement in the determination of the most sensitive regions to corrosion, which were found to be the heat affected (HAZ) and the thermomechanically affected (TMAZ) zones of the advancing side of the weld tool. They also showed that the regions affected by the welding procedure have a lower corrosion resistance than the base metal. By using Local Electrochemical Impedance Spectroscopy (LEIS), it was shown that the galvanic coupling between the different areas generated during the welding process does not need to be taken into account in the description of the corrosion process, which is at odds with the results published in several studies of this alloy welded by FSW. The work also present an original theoretical contribution, demonstrating that contact-angle measurements and electrochemical impedance spectroscopy in a sessile drop can be used simultaneously to determine the capacity of the interface. The theoretical model predictions were confirmed by the experimental results obtained both with a model system and in the different regions generated by FSW of aluminum alloy 2024-T3.

A redução de peso é uma questão tecnológica fundamental para a indústria aeroespacial, uma vez que diminui o consumo de combustível, resultando em redução de custos e contribuindo para a redução da emissão de gases de efeito estufa. Devido à relação favorável entre resistência mecânica e peso, as ligas de alumínio de elevada resistência mecânica contribuem favoravelmente para este aspecto. Entretanto, como estas ligas são dificilmente soldáveis pelos processos tradicionais envolvendo fusão, o procedimento de junção utilizado em aeronaves é a rebitagem, resultando em ganho de peso. O processo de soldagem por fricção (friction stir welding -FSW), desenvolvido no início dos anos noventa pelo The Welding Institute (TWI) do Reino Unido, se constituiu em um grande avanço para a soldagem das ligas de alumínio utilizadas na indústria aeroespacial, pois permite a produção de soldas mais confiáveis e virtualmente livres de defeitos. Entretanto, o aquecimento das peças e a deformação mecânica durante a FSW geram zonas com diferentes características microestruturais que, de acordo com a literatura, apresentam resistências à corrosão diferentes. Por oferecerem elevada resolução lateral, as técnicas eletroquímicas locais são úteis para elucidar as diferenças de reatividade local de eletrodos heterogêneos, como no caso de metais soldados. No presente trabalho técnicas eletroquímicas locais foram empregadas para caracterização da resistência à corrosão em meio contendo cloreto das diferentes zonas geradas pela soldagem de topo da liga de alumínio 2024-T3 por FSW, comparando-a com a exibida pelo metal base. O estudo foi complementado com a caracterização microestrutural destas regiões e também por ensaios macroscópicos de corrosão. Os resultados dos procedimentos de caracterização microestrutural confirmaram que a FSW provoca modificações na microestrutura das regiões afetadas pelo processo, principalmente no que concerne à distribuição das nanopartículas precipitadas durante o envelhecimento natural da liga. Por sua vez, os resultados dos ensaios macroscópicos de corrosão e eletroquímicos locais mostraram-se concordantes na determinação da região mais sensível à corrosão, que foi verificada como sendo as zonas termicamente afetada (Heat Affected Zone - HAZ) e termomecanicamente afetada (Thermomechanically Affected Zone - TMAZ) do lado do avanço da ferramenta de soldagem, mostrando também que as regiões afetadas pelo processo de soldagem apresentam resistência à corrosão inferior à do metal base. Através do uso da espectroscopia de impedância eletroquímica local (Local Electrochemical Impedance Spectroscopy - LEIS) foi evidenciado que o acoplamento galvânico entre as diferentes zonas geradas durante o processo de soldagem não desempenha um papel relevante na aceleração do processo corrosivo, o que está em desacordo com os resultados publicados em diversos estudos realizados com esta liga soldada por FSW. O trabalho apresenta ainda uma contribuição teórica original demonstrando que medidas de ângulo de contato e de espectroscopia de impedância eletroquímica em uma gota séssil podem ser usadas simultaneamente para a determinação da capacitância da dupla camada elétrica. As previsões do modelo teórico foram confirmadas tanto através de resultados obtidos com um sistema modelo como também em determinações realizadas nas diferentes regiões geradas pela soldagem por FSW da liga 2024-T3. / Weight reduction is a fundamental technological issue for the aerospace industry, as it decreases the fuel consumption, resulting in reduced both costs and greenhouse gases emission. Due to the favorable relation between strength and weight, high strength aluminum alloys favorably contribute to this aspect, but they remain difficult to weld by conventional processes involving fusion, and, therefore, the junction procedure used in aircraft is riveting, resulting in weight gain. The friction stir welding (FSW) process, developed in the early nineties by the \"The Welding Institute\" (TWI), United Kingdom, is a major breakthrough for the welding of aluminum alloys as it allows the production of more reliable and virtually defect-free welds. However, the heating of the parts and the mechanical deformation during FSW generate zones with different microstructures with different corrosion resistances. As they offer high lateral resolution, local electrochemical techniques are useful for elucidating differences in local reactivity of heterogeneous electrodes, as the case of welded metals. In the present work, local electrochemical techniques were employed to characterize the corrosion resistance in chloride environment of the different zones generated by butt welding the 2024-T3 aluminum alloy by FSW, and to compare this response with that displayed by the base metal. The study was complemented with the microstructural characterization of these regions and also by macroscopic corrosion tests. The results of the microstructural characterization confirmed that FSW causes changes in the microstructure of the regions affected by the process, especially with regard to the distribution of the precipitated nanoparticles during the natural aging of the alloy. The results of the macroscopic corrosion and of the local electrochemical tests showed good agreement in the determination of the most sensitive regions to corrosion, which were found to be the heat affected (HAZ) and the thermomechanically affected (TMAZ) zones of the advancing side of the weld tool. They also showed that the regions affected by the welding procedure have a lower corrosion resistance than the base metal. By using Local Electrochemical Impedance Spectroscopy (LEIS), it was shown that the galvanic coupling between the different areas generated during the welding process does not need to be taken into account in the description of the corrosion process, which is at odds with the results published in several studies of this alloy welded by FSW. The work also present an original theoretical contribution, demonstrating that contact-angle measurements and electrochemical impedance spectroscopy in a sessile drop can be used simultaneously to determine the capacity of the interface. The theoretical model predictions were confirmed by the experimental results obtained both with a model system and in the different regions generated by FSW of aluminum alloy 2024-T3.

The present study investigates the effect of fluorine species during anodizing of aluminium and AA2024-T3 alloy in sulphuric acid and tartaric-sulphuric acid (TSA) electrolytes. The investigation comprises four main parts; (i) Effects of fluoride on barrier film formation on aluminium. (ii) Effects of fluoride and fluorozirconic acid (FZ) on porous film growth on aluminium in sulphuric acid. (iii) Effects of FZ on porous film growth on aluminium and AA 2024-T3 alloy in sulphuric acid and TSA. (iv) Effects on anodizing of other fluoroacids (fluoroboric (FB), fluorosilicic (FS) and fluorotitanic acid (FT)). The anodic films were examined by analytical scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Rutherford backscattering spectroscopy, nuclear reaction analysis and glow discharge optical emission spectroscopy. The behaviour of fluoride ions during the growth of barrier-type films on aluminium was investigated in ammonium pentaborate solution with added sodium fluoride. Additions of up to 3.5 x 10-3 M sodium fluoride had a negligible influence on the film growth. In contrast, 3.5 x 10-2 M sodium fluoride reduced the efficiency to 60% as fluoride ions promoted field-assisted ejection of Al3+ ions from the film. Incorporated fluoride ions migrated inwards at a rate about twice that of O2- ions, forming a fluoride-rich layer at the film base. The study of the influence of FZ on formation of porous anodic films in sulphuric acid and TSA employed a range of anodizing voltages, electrolyte temperatures and anodizing times. Fluoroacid increased the growth rate, with a reducing influence as the temperature increased. The films contained fluoride and sulphate ions, zirconium was not detected. The fluoride concentration decreased with increasing temperature, whereas the sulphate concentration was unaffected. Anodizing aluminium and AA 2024-T3 alloy in other fluoroacids resulted in similar influences on the anodizing behaviour as FZ. The differences in growth rate, film composition and film morphology were comparatively small and did not show a systematic dependence on the type of fluoroacid employed. Boron, silicon and titanium were not detected in the films.

In this work, the nucleation and growth of pores in anodic films formed on aluminium in chromic acid and the effect of low levels of sulphate impurity in the anodizing bath on the formation of the films on aluminium and AA 2024 alloy are investigated. The sulphate concentrations considered include levels within specified limits for industrial processing. The anodizing is carried out either potentiostatically or by stepping the voltage. The films are examined by scanning electron microscopy, transmission electron microscopy and atomic force microscopy to determine the pore spacing, pore population densities, pore diameters and film thicknesses. Film compositions were determined using energy-dispersive X-ray spectroscopy, Rutherford backscattered microscopy and nuclear reaction analysis. In order to investigate the mechanism of pore formation, two tracer methods are employed. In one method, anodic films are formed first in an arsenate electrolyte in the second method, a tungsten tracer band deposited by magnetron sputtering. The behaviours of arsenic and the tungsten are investigated during the subsequent anodizing in chromic acid. The results suggest that the initiation and growth of pores in occurred as a result of electric field assisted chemical dissolution. The effect of sulphate impurity in the chromic acid is investigated using electrolytes with different sulphate content. In the initial stages of anodizing aluminium at 100 V, sulphate impurity at a level of 38 ppm in the chromic acid is shown to lead to significant incorporation of sulphate ions into the anodic film, a lower current density, a smaller cell size and less feathering of the pore walls. In addition, the efficiency of film formation is increased. In later stages of anodizing, the growth of larger pores and cells, leads to a duplex film morphology, with finer pores in the outer region. The change in pore size correlates with a reduction in the incorporation of sulphate into the film. From the results of sequential anodizing experiments, it is suggested that incorporated sulphate ions generate a space charge layer, which has an important role in determining the current density. The effects of higher sulphate concentrations up to 3000 ppm are investigated, which are shown to significantly affect the current density and the pore diameter. Anodizing of aluminium and AA 2024 alloy was also carried out according to industrial practice. The results show that there is significant effect of sulphur impurity on the film thickness. Corrosion tests in 3.5 % NaCl solution for the alloy after anodizing in low (smaller or equal to 1.5 ppm) and high (~38 ppm) sulphate-containing chromic acid electrolytes demonstrate a better corrosion resistance with films formed in the latter electrolyte.

A numerical simulation is conducted using LS-DYNA to simulate hard projectile impact on a friction stir welded (FSW) plate. As the hard projectile has a wide range of velocity, mass and shape, when referring to AMC 25.963(e) of CS-25, ―Fuel Tank Access Cover‖, the hard projectile can be defined as 9.5 mm cubic-shaped steel engine debris with an initial impact velocity of 213.4 m/s (700 ft/s). This preliminary study was to evaluate whether the fuel tank adjacent skin panel joined by FSW would pass the regulation. First, the geometry and Johnson-Cook material model of the FSW joint were developed based on previous experimental research and validated by comparison with the tensile test on the FSW specimen. Then the impact on an Aluminium Alloy 2024 (AA 2024) plate without FSW was modelled. The minimum thickness of a homogeneous AA 2024 plate which could withstand the impact from engine debris is 3 mm. Finally the impact on 3 mm thick AA 2024 FSW plate was simulated. The welding induced residual stress was implemented in the plate model. The impact centre was changed from the nugget zone to the thermo-mechanically affected zone, heat-affected zone and base material zone of the FSW joint. Penetration only occurred in the model with impact centre on the nugget zone. Additional simulation indicated that increasing the thickness of the FSW plate to 3.6 mm could prevent the penetration.

The objective of this study was to investigate the low velocity impact behavior of both monolithic and laminated aluminum alloy plates. For this purpose, a drop-weight test unit was used. The test unit included the free fall and impact of an 8 kg hammer with an 8 mm punching rod from 0.5 m to 4 m. The relationship between the change in static mechanical properties (hardness, ultimate tensile strength, yield strength, strain hardening rate) and low velocity impact behavior of monolithic aluminum plates were investigated. Tested material was AA 2024, heat treatable aluminum alloy, which was artificially aged to obtain a wide range of mechanical properties. In the second stage of the study, the relationship between the low velocity impact behavior of laminated plates was compared with that of monolithic aluminum plates at identical areal densities. For this purpose, a series of AA 2024 thin plates were combined with different types of adhesives (epoxy, polyurethane or tape). Finally, fracture surface of the samples and microstructure at the deformation zone were examined with both scanning electron microscope and optical microscope. It is found that the ballistic limit velocities of AA 2024 plates increase with increase in hardness, yield strength and ultimate tensile strength. It is also found that a linear relation exists between the ballistic limit velocity and strain hardening rate or hardness. When the low velocity impact behaviors of laminated and monolithic targets were compared, it was seen that monolithic targets have a higher ballistic limit velocity values for from the 2.5 to 10 mm thick targets. It was also observed that adhesives are not so effective to strengthen the low velocity impact performance. On the other hand, with increasing Charpy impact energy, penetration and perforation behaviors are getting worse in 10 to 30 joules energy range. Different types of failure mechanisms involving, plugging, dishing, stretching and bending were determined. For high strength and thick plates plugging type deformation was leaded. In contrast, for thinner and weaker targets bending, stretching and dishing type failures were dominating. For laminated targets also dishing type failure was determined.

No description available.

In recent times, application of aluminum alloys is favored in the transportation sectors such as the aerospace and automobile industries where reduced fuel consumption and greenhouse gas emission are major priorities. In these applications, these alloys can be exposed to dynamic shock loading conditions as in the case of car crash and birds’ collision during aircraft’s take-off or landing. This study therefore focused on the deformation and damage mechanisms in AA 2017, AA 2024 and AA 2624 aluminum alloys under both quasi-static and dynamic impact loading conditions. Cylindrical specimens of the selected aluminum alloys were investigated under both quasi-static loading at 3.2 x10-3 s-1 using an Instron R5500 mechanical testing machine and dynamic impact loading using the split Hopkinson pressure bar at strain rates ranging between 2000 and 8000 s-1. The effects of strain rate and temper condition on the microstructural evolution in the alloys during mechanical loading were studied. The electron backscatter diffraction (EBSD) technique was used to investigate the texture of the naturally-aged AA 2017 and AA 2624 alloys before and after dynamic shock loading. The contributions of the major alloying elements such as copper, magnesium and silicon to the microstructural evolution and deformation behavior of the alloys under the dynamic shock loading condition were also studied using the energy dispersive spectroscopy (EDS) technique. Results showed that the morphology and atomic distribution of particles in the investigated alloys are functions of the temper condition. The hardness of all the three alloys was higher in the age-hardened conditions than the annealed ones. Although deformation of the alloy under quasi-static compressive loading was dominated by strain hardening, flow softening leading to strain localization and formation of shear bands occurred once certain critical strain values were reached. Under both quasi-static and dynamic loading, the alloys with low Cu:Mg ratio (AA 2024 and AA 2624) showed higher mechanical strength in age-hardened condition than that with high Cu:Mg ratio (AA 2017). All the alloys in the annealed condition exhibited an enhanced plasticity and formability. Intense strain localization leading to formation of adiabatic shear bands (ASBs) was the principal contributor to failure in the alloys under dynamic impact loading. Both deformed and transformed bands were observed, with cracking occurring mainly along the transformed shear bands. The tendency for formation of adiabatic shear bands is observed to be a function of the alloy composition, temper condition, strain, strain rate and strain hardening rate. In the natural aging condition, AA 2024 showed the highest susceptibility to formation of ASBs followed by AA 2624 and AA 2017 in that order. On the other hand, AA 2024 has the least susceptibility in the artificially-aged condition. Occurrence of bifurcation of transformed bands in dynamic impacted specimens is dependent on temper condition, strain and strain rate. The mechanism of fracture of the precipitation hardened samples is typical of ductile fracture occurring sequentially by nucleation, growth, and coalescence of micro-voids processes within transformed band. Elongated grains were observed to arrest propagating shear band depending on the angle the band makes with elongated grains. The higher the angle of inclination of a shear band to the grain on its path, the higher the tendency of the grain to stop its propagation. Texture analysis of the impacted specimens of AA 2017-T451 and AA 2624-T351 shows that the former has a higher tendency for the evolution of ultra-fine DRX grains within the transformed shear band. High strain rate led to the development of CD//<111> orientations at the expense of CD//<110> orientations. Schmid factor calculations performed on few different orientations in the starting microstructure shows that CD//<110> is less susceptible to slip deformation and consequently underwent rotation to CD//<111>.

Les couches de conversion actuellement utilisées dans l'industrie aéronautique, pour protéger le métal de la corrosion et favoriser l'adhérence de la peinture, contiennent du chrome hexavalent, composé toxique et cancérigène dont l'utilisation va prochainement être interdite par la réglementation européenne REACh. L'une des pistes envisagée pour remplacer ces couches chromatées est l'utilisation de couches de conversion TCP (Trivalent Chromium Protection). Ces travaux portent sur l'étude des couches de TCP et s'attachent à caractériser chaque étape du traitement de surface industriel, incluant les étapes de prétraitement et de post-traitement. Des techniques d'analyse de surface (XPS, ToF-SIMS, AFM, MEB et PM-IRRAS) ont été utilisées pour analyser la composition chimique et la morphologie de la surface après chaque étape du traitement. Cette étude a été réalisée sur un alliage d'aluminium AA 2024-T3, très utilisé en aéronautique pour ses propriétés mécanique, mais présentant une faible résistance à la corrosion. Les résultats obtenus ont notamment mis en évidence que la couche de TCP se forme sur toute la surface de l'alliage (composés intermétalliques et cavités), et ont permis de comprendre comment le post-traitement permet d'améliorer la résistance à la corrosion de la couche de TCP. Ces travaux s'intéressent également à des couches de conversion sans chrome, à base de zirconium, étudiées ici pour servir de point de départ au développement d'une conversion sans chrome qui respecterait les exigences de résistance à la corrosion. / Conversion coatings are used in aerospace industry to protect the metal from corrosion and to promote paint adhesion. Currently, chromate conversion coatings are used, but chromate is toxic and carcinogenic and its use will be forbidden by the European REACh regulation. TCP (Trivalent Chromium Protection) conversion coatings, are considered as a promising alternative to replace chromate conversion coating. This work focuses on the characterisation of the TCP layer and considers each step of the industrial surface treatment, including pre-treatment and post-treatment steps. Surface analytical techniques (XPS, ToF-SIMS, AFM, SEM and PM-IRRAS) were used to analyse the chemical composition and morphology of the surface after each step in the process. This work was done on an aluminium alloy AA 2024-T3, commonly used in the aerospace industry for its good mechanical properties, but poorly resistant to corrosion. The results obtained demonstrate, among other things, that the TCP layer totally covers the surface (intermetallic compounds and cavities) and enable to understand how the post-treatment can improve the corrosion resistance of the TCP coating. This work also focuses on conversion coating based on zirconium, which are studied here to be used as a starting point to develop a new conversion coating without chromium, meeting the corrosion resistance requirement.