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Al-Zn-Mg-Cu-Zr based AA7010 aluminum alloy belongs to the class of heat treatable alloys and the semi-finished products are generally produced by hot rolling, forging or extrusion processes. It is well known that the thermo-mechanical processing parameters strongly influence both the evolution of texture as well as microstructure in the material. As a result, the semi-finished products exhibit anisotropy in mechanical properties causing legitimate concerns on the applicability of the alloys. In the present thesis, a systematic study on the evolution of texture and microstructure and its implications on the mechanical properties anisotropy of AA7010 alloy has been attempted. A brief introduction on the development of texture and its influence on the anisotropy of the mechanical properties of 7xxx series aluminum alloys is presented first with a view to explore the scopes for further investigation. An overview of the relevant literature is described subsequently. The development of texture and microstructure in an Al-Zn-Mg-Cu-Zr based 7010 aluminum alloy during uneven, hot cross-rolling is presented. Materials processing involves three different types of uneven cross-rolling. The variations in relative intensity of the β-fibre components as a function of cross rolling modes have been investigated. It has been shown that the main attributes to the texture evolution in the present study are (a) cross-rolling and inter-pass annealing that reduce the intensity of Cu component following each successive pass, (b) recrystallization resistance of Bs oriented grains, (c) stability of Bs texture under cross-rolling, and (d) Zener pinning by Al3Zr dispersoids. The stability of the unique single, rotated Brass-{110}(556) component developed in the present alloy, during long term thermal annealing and cold rolling deformation has been systematically investigated further. Subsequently, the influence of development of microstructure and texture on the in-plane anisotropy (AIP) of yield strength, work hardening behavior and yield locus anisotropy has been presented. The AIP and work hardening behavior are evaluated by tensile testing at 0o, 45o and 90o to the rolling direction, whilst yield loci have been generated by Knoop hardness method. It has been observed that in spite of having strong rotated Brass texture, the specimens show low AIP especially in peak aged temper. The in-plane anisotropy (AIP) of yield strength, and work hardening behavior of a heat treated 7010 aluminum alloy sheet having strong, rotated Brass-{110}556 component with different texture intensity and volume fraction of recrystallization has been further evaluated. It is observed that the AIP increases with increase in texture intensity and volume fraction of recrystallization. In the subsequent chapter, the tensile flow and work hardening behavior are described using constitutive equations. Room temperature tensile properties have been evaluated as a function of tensile axis orientations in as-hot rolled as well as peak aged conditions. It has been found that both the Ludwigson and a generalized Voce-Bergström relation adequately describe the tensile flow behavior in all conditions compared to the Hollomon relation. The Voce-Bergström parameters define the slope of - plots in the stage-III regime when the specimens show a classical linear decrease in hardening. Further analysis of work hardening behavior throws light on the effect of texture on the dislocation storage and dynamic recovery. An overall summary of the experimental results and the scopes for future studies have been presented at the end.

The automotive industry is expected to transition from a net-consumer to a net-producer of aluminum scrap as aluminum-intensive vehicles (AIVs, i.e., Ford’s aluminum-bodied F-150) begin to reach end-of-life (EOL). In the past, the industry has downcycled aluminum scrap to meet the consumption demands of the automotive sector. With the shift to having a large supply of this scrap in the near future, the industry needs to recover and reuse EOL Al by utilizing a circular economic model, create value via an upcycling paradigm (vs downcycling). This work establishes a platform as to how the recycling industry can be restructured to create value in our waste streams and is organized in three segments: First, an analysis of the flow of automobiles at EOL was carried out from the perspective of recovery and reuse; a recycling rate for Al has been determined, and the factors that go into the dynamics of the recycling rate have been identified. Secondly, the current state of the market was surveyed to evaluate where improvements could be made to affect material collection and recovery. The latter led to compositional characterization of aluminum auto-shred to identify the alloys in the mixture, and thereby the needed intelligent sorting systems for upcycling. Thirdly, these results were used in a dynamic material flow model to predict how the composition of auto-shred will change due to increased aluminum usage and as a function of various end-of-life processing scenarios. The outcome and impact of this work is that we have established a platform that enables the ELV recycling industry to upcycle the large amount of Al that will be available in the near future. These results will be discussed and reviewed during this presentation.

L'élaboration de nouveaux alliages maintient un fort intérêt pour le phénomène d’instabilité plastique, ou l'effet Portevin-Le Chatelier (PLC), provoqué par l'interaction des dislocations avec des atomes de soluté. Par ailleurs, l'effet PLC attire l'intérêt comme un exemple remarquable d'auto-organisation dans les systèmes dynamiques. Il est associé à des motifs complexes de séries de chutes de contrainte liées à la nucléation et au mouvement des bandes de déformation dans le matériau déformé, et nécessite une compréhension de l'auto-organisation des dislocations. La déformation plastique des alliages Al-Mg est sujette à l'instabilité dans une large gamme de conditions expérimentales. Pour cette raison, les alliages Al-Mg binaires ont longtemps servi d'objets modèles pour l'étude de l'effet PLC. En même temps, l'utilisation pratique des alliages binaires Al-Mg est limitée en raison d’une faible résistance mécanique. Une amélioration significative de leurs propriétés peut être atteinte en ajoutant des solutés supplémentaires, conduisant en particulier à la formation de précipités. En outre, une forte réduction de la taille de grains du polycristal pourrait être une technique clé pour produire des matériaux à haute résistance et ténacité. Cependant, il existe très peu d'information, souvent contradictoire, sur l'instabilité PLC dans les alliages Al-Mg à grains fins et contenant des précipités. Le but de l'étude de cette thèse a été d'étudier les caractéristiques spécifiques de l'effet PLC dans les alliages à base AlMg, avec et sans nanoparticules, à gros grains et à grains fins, ces derniers obtenus par une méthode de déformation plastique sévère. Grâce à l’application de méthodes d’extensométrie locale, notamment de la technique de corrélation d’images, ces études ont révélé une persistance non habituelle de la propagation des bandes de déformation dans les alliages comprenant des précipités et/ou des grains fins. Ce mode dynamique est observé dans un large intervalle de vitesses de déformation, tandis qu’il n’apparait qu’à haute vitesse dans des alliages modèles AlMg. Par ailleurs, l’analyse des distributions statistiques des amplitudes des chutes de contrainte a révélé une tendance vers une statistique en loi puissance, caractéristique du mode de propagation. Ce phénomène est attribué à une modification du couplage spatial entre les dislocations, due à la concentration de contraintes internes. La combinaison de ces études avec l’analyse de l’émission acoustique a mis en évidence une influence de la microstructure sur la compétition entre un facteur aléatoire et la synchronisation des dislocations. Enfin, l’étude par corrélation d’images a permis d’observer une interrelation entre l’instabilité PLC et la formation de la striction. / The elaboration of new alloys sustains a strong interest to the phenomenon of unstable plastic flow, or the Portevin–Le Chatelier (PLC) effect, caused by interaction of dislocations with solute atoms. Moreover, this effect attracts interest as a rich example of self-organization in dynamical systems. It is associated with complex patterns of stress serrations related to nucleation and motion of deformation bands in the deforming material, and requires understanding of self-organization of dislocations. Plastic deformation of Al-Mg alloys is prone to instability in a wide range of experimental conditions. For this reason, binary Al-Mg alloys served for a long time as model objects for investigation of the PLC effect. At the same time, the practical use of binary Al-Mg alloys is limited because of their low strength. A significant improvement of their properties can be achieved by additional alloying, in particular, leading to precipitation. Further, extensive grain refinement could be a key technique used to produce tough and high- strength materials. However, there exists very limited and often contradictory information on the PLC instability in fine-grained Al-Mg alloys containing precipitates. The objective of the present thesis was to investigate specific features of the PLC effect in AlMg-based alloys with and without nanoscale particles, both in coarse-grained and fine-grained states, the latter obtained by severe plastic deformation. Using local extensometry methods, particularly the image correlation technique, these studies revealed an unusual persistence of the propagation of deformation bands in alloys with precipitates and/or fine grains. This dynamic mode is observed in a wide range of strain rates, whereas it only appears at high strain rate in model Al-Mg alloys. Moreover, the analysis of statistical distributions of stress drop amplitudes revealed a tendency to power law statistics characteristic of the propagation mode. This phenomenon was attributed to a modification of the spatial coupling between dislocations due to the concentration of internal stresses. The combination of these studies with the acoustic emission analysis uncovered an influence of the microstructure on the competition between a random factor and the dislocation synchronization. Finally, the study by the image correlation made it possible to observe an interrelation between the PLC instability and the neck formation.

Várias ligas de Al em cavacos, com diferentes granulometrias foram dissolvidas de modo convencional, com ataque por água régia. Este tipo de decomposição resulta, muitas vezes, em resíduos sólidos, cujas quantidades dependem dos teores de silício. A fim de se comparar os resultados, procedeuse, com esses resíduos, de dois modos distintos: ou foram desprezados ou foram decompostos com ácido fluorídrico, eliminando-se o silício, dissolvendo-se o restante com ácido nítrico e agrupando-o à primeira solução para a determinação de Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb, Sn, Ti e Zr por ICP-OES. Foi avaliada a influência de quantidades crescentes de Al na determinação destes elementos e, também, a provável interferência espectral de Cu na determinação do Zn (com e sem separação eletrolítica de Cu). A dissolução eletrolítica de ligas de alumínio em cavacos foi estudada pressionando-os contra um eletrodo de platina para que se comportassem como se fossem o próprio ânodo e a eletrólise ocorresse. Uma célula foi construída utilizando-se um tubo (corpo de seringa de 2,5 mL) com perfurações ao redor da base aberta, onde foi colocada uma malha sintética (perlon) no fundo e, sobre esta, a amostra. Na parte superior foi introduzido um pequeno tarugo de acrílico com um fio de platina passando pelo seu interior e com um orifício por onde passava o fluxo (4,5 mL min.-1) da solução eletrolítica (ácido nítrico diluído). Na extremidade inferior, prendeu-se, com o fio, uma plaquinha, também de platina, que pressionava a amostra. A solução saía pelos orifícios inferiores para um béquer de onde era recirculada e onde estava colocado o cátodo, um fio de Pt (de forma de losango), sendo novamente captada e introduzida na parte superior do tarugo do ânodo. Com esse circuito, foram obtidos bons resultados utilizando-se ácido nítrico 1 mol L-1, corrente de 0,6A e tempo de eletrólise de 10 minutos. Sendo a dissolução parcial, é necessário que se conheçam as porcentagens dos elementos por dissolução ácida total de uma liga de composição similar ou por um material de referência certificado. Normalizaram-se os dados pelas porcentagens conhecidas dos constituintes das ligas. Compararam-se os cálculos feitos dos seguintes modos: 1-) pela razão entre a concentração do elemento com a do Al, também determinada; 2-) pela a razão entre a concentração do elemento com a soma das concentrações de todos os elementos determinados, inclusive o Al; 3-) pela razão entre a concentração do elemento e a soma das concentrações só dos outros elementos, sem o Al. O desvio padrão e o erro relativo para os elementos Fe, Cu, Mg, Ni e Cr, quando em teores > 0,1%, foram < 10%; para teores de Zn < 0,2%, foram menores de 10% e para teor de 4,8% foram < 15%. Já para o Mn, quando em teor > 0,2% foram <10% (exceto para a liga B.C.S.268/1). O desvio padrão relativo para o Zr, com teor ao redor de 0,002% foi <10%. Os resultados para o elemento Pb nas ligas B.C.S. 216/1 e 380 tiveram desvio padrão e erro relativo <10%, mas o mesmo não ocorreu na liga B.C.S. 268/1. O elemento Sn apresentou resultados piores, ao redor de 20%. O elemento Ti só deu bons resultados quando em teor de cerca de 0,2%. Para estas determinações foram avaliadas as dissoluções químicas dos metais nas ligas pelo ácido nítrico em diferentes concentrações e temperaturas. Além disso, foram avaliadas duas outras células para a verificação da possibilidade de dissolução eletrolítica das ligas de Al on-line com a determinação por ICP-OES. / Several aluminum alloys with different chips size were dissolved using aqua regia (HCl:HNO3,3:1). The residues of the dissolution procedure were either rejected or used in silicon volatilization with hydrofluoric acid before determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb, Sn, Ti and Zr by ICP-OES. The influence caused by crescent amounts of aluminum in the determination of other elements and the probable spectral interference by Cu in determination of Zn (with or without electrolytic separation of Cu) was evaluated. The electrolytic dissolution of aluminum alloys was performed by pressing chips against a platinum electrode for the electrolysis to occur, so that way the chips behaved as the anode. A tube (body of syringe of 2.5mL) with perforations around the open base was used to contain the sample and Pt electrode. The alloy was placed on synthetic wool (perlon) in this tube. An acrylic dowel with a platinum wire across its interior was fixed in the superior part a tube with Teflon film, with an orifice through which the electrolytic solution flowed (HNO3 1 mol L-1; 4.5mL min-1). A platinum dish was fixed at the inferior extremity of the platinum wire to press the sample. The solution came out through the inferior orifices of the tube to a flask, from where it was again captured (with a peristaltic pump) to go into the superior part of the tube. In this flask, a Pt wire cathode was also placed. A current of 0,6A and ten minutes of electrolysis provided good results. Due to the partial dissolution, the knowledge of percentages of previous elements analyzed after total dissolution, or using certified reference material are necessary. The results were normalized by known percentages. The calculations were made by: 1-) the ratio between the concentration of the element determind, with the determined concentration of aluminum; 2-) the ratio between concentration of the element and the sum of the concentrations of the elements determined, including Al; 3-) the ratio between the concentration of element and the sum of the concentrations of the elements determined, without the aluminum. The relative standard deviations and accuracy were <10% for the elements Fe, Cu, Mg, Ni and Cr when the concentrations were >0.1%; for the Zn were 15%, when the concentration >0.2%, and <10% for concentration <0.2%. For Ti with concentration of about 0.1%, were 15%. Relative standards deviations for the Zr, with concentration of 0.002%, were always <10%. The element Pb, Sn and Mn didnt provide good results. For these determinations, the chemical dissolution of the elements with different nitric acid concentrations and temperature was evaluated. Two other cells for the electrolytic dissolution of Al alloys followed by online ICP-OES determination were examined.

A soldagem por fricção (Friction Stir Welding - FSW) é um processo eficiente de unir ligas de alumínio de alta resistência evitando defeitos que são usualmente criados quando técnicas convencionais de soldagem são utilizadas. A indústria aeronáutica tem mostrado grande interesse neste método de soldagem, tanto para a união de ligas similares como dissimilares. Entretanto, este processo causa modificações microestruturais dependentes das condições de tratamento térmico ou termomecânico. Contato elétrico entre zonas de microestruturas diferentes, por sua vez, pode resultar em acoplamento galvânico. No presente estudo, a soldagem por FSW foi usada para unir duas ligas de alumínio dissimilares, AA2024-T3 e AA7475-T651 e o efeito desta soldagem na resistência à corrosão das juntas soldadas e na microestrutura das ligas foi avaliada. Na investigação da resistência à corrosão foram utilizados ensaios eletroquímicos, especificamente, medidas de potencial de circuito aberto (OCP) em função do tempo de exposição ao meio corrosivo, ensaios de polarização e de espectroscopia de impedância eletroquímica, global (EIS) ou local (LEIS), em duas soluções, seja 0,1 M Na2SO4 ou 0,1 M Na2SO4 + 1 mM NaCl. Os ensaios eletroquímicos evidenciaram efeito de acoplamento galvânico nas juntas soldadas. A caracterização microestrutural foi realizada por microscopia ótica, microscopia eletrônica de varredura, microscopia eletrônica de transmissão e por calorimetria diferencial. As zonas afetadas pela solda tiveram importantes modificações na microestrutura indicadas pela precipitação e dissolução de precipitados que afetam a resistência à corrosão localizada. A resistência à corrosão intergranular e a resistência à esfoliação das juntas soldadas também foram avaliadas e comparadas com as das ligas AA2024-T3 e AA7475-T651 não soldadas. Os resultados mostraram aumento da suscetibilidade das juntas soldadas a estas formas de corrosão em comparação com as ligas não soldadas sendo observado ataque mais severo na liga AA7475-T651. A identificação das áreas anódicas e catódicas resultantes do acoplamento galvânico nas juntas soldadas foi realizada por teste que consistiu na deposição de camada de gel (ágar-ágar) com indicador universal na superfície das ligas soldadas. A liga AA2024-T3 atuou como cátodo, enquanto a AA7475-T651, como ânodo no par galvânico. Além disso, evolução de hidrogênio foi observada na região de interface entre a zona termomecanicamente afetada e a termicamente afetada da liga AA7475-T651 mostrando que reações catódicas também ocorreram localmente nesta última liga. Resultados de LEIS obtidos nas diferentes zonas das duas ligas soldadas por FSW mostraram acoplamento galvânico na interface entre elas para tempos curtos de ensaio e deslocamento da região mais ativa com o tempo de ensaio para a liga AA7475-T651, mais precisamente para a interface entre a zona termomecanicamente afetada e a térmicamente afetada desta liga. / Friction Stir Welding (FSW) is an efficient process of joining high strength aluminum alloys avoiding defects that are usually created when conventional welding techniques are used. The aircraft industry has shown great interest in this welding method, both for welding of similar or dissimilar alloys. However, this process causes microstructural changes that are dependent on the thermal or thermomechanical conditions applied. Electrical contact between zones of different microstructures, in turn, can result in galvanic coupling. In the present study, FSW was used to join two dissimilar aluminum alloys, AA2024-T3 and AA7475-T651 and the effect of this process on the corrosion resistance of the welded joints and on the microstructure of the alloys was evaluated. For corrosion resistance evaluation, electrochemical tests were used, specifically, open circuit potential measurements (OCP) as a function of time of exposure time to the corrosive environment, polarization tests, and electrochemical impedance spectroscopy, global (EIS) or local (LEIS), in two solutions, either 0.1 M Na2SO4 or 0.1M Na2SO4 + 1 mM NaCl. The electrochemical tests showed galvanic coupling effects in the welded joints. Microstructural characterization was carried out by optical microscopy, scanning electron microscopy, transmission electron microscopy and differencial scanning calorimetry. The welded affected zones showed significant microstructural changes indicated by precipitation and dissolution of precipitates that affect the localized corrosion resistance. Intergranular and exfoliation corrosion resistance of the welded joints were also evaluated and compared to those of unwelded AA2024-T3 and AA7475-T651 alloys. The results showed increased susceptibility of welded joints to these forms of corrosion in comparison with the unwelded alloys with more severe attack associated to the AA7475-T651 alloy. Identification of anodic and cathodic areas due to galvanic coupling in the welded joints was evaluated by a test consisting in depositing a gel layer (ágar-ágar) with universal indicator on the surface of the welded alloys. The AA2024-T3 alloy worked as cathode, while the AA7475-T651 as anode in the galvanic coupling. Furthermore, hydrogen evolution was observed at the interface region between the thermomechanically affected zone and the heat affected alloy AA7475-T651 showing that cathodic reactions also occurred on this last alloy. LEIS results obtained in different zones of the two FSW welded alloys showed galvanic coupling at the interface between them for short test times and displacement of the most active region to the AA7475-T651 alloy, at longer periods of test, specifically to the interface between the thermomechanically affected and the heat affected zones of this last alloy.

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