L'alimentation en composants est un problème majeur dans la conception des systèmes de production et plus particulièrement d'assemblage. Un système d'alimentation doit garantir la position et l'orientation des composants qu'il fournit au système d'assemblage, quelle que soit la taille des composants. En revanche, le niveau de précision sera généralement d'autant plus important que les composants sont petits. Nos travaux ont été réalisés dans le contexte de l'alimentation en composants de taille millimétrique à microscopique avec des objectifs de modularité et de haute précision de positionnement. La première contribution de la thèse a consisté à élaborer une stratégie pour l'alimentation de haute précision en composants millimétriques pour une architecture ouverte, flexible et standardisée, proposée par un projet européen EUPASS (Evolvable Ultra Precision ASembly System). Un système standard a ainsi été développé. Il est modulaire, reconfigurable pour différents types de minicomposants et permet leur maintien micrométrique. Sur la base de ces travaux, nous avons étendu notre étude aux systèmes de micro-assemblage (microusine). L'objectif était de déplacer dans un plan des micro-objets jusqu'à une position donnée. L'idée retenue se fonde sur l'utilisation des vibrations pour entraîner ces micro-objets par inertie. Il a donc été nécessaire de caractériser les interactions entre la surface du système d'alimentation et la surface du micro-objet. Pour cela nous avons élaboré une méthode pour évaluer directement la force concernée qui est la force de friction. Le contrôle des vibrations du système a ensuite été conçu. Le pas de déplacement d'un micro-objet en fonction de ses caractéristiques est alors maîtrisé. Enfin, une boucle d'asservissement permet de contrôler le déplacement des micro-objets jusqu'à une position consigne.

The goal of this thesis is on improving the understanding of mechanical and tribological mechanisms in microelectronic wire bonding. In particular, it focusses on the development and application of quantitative models of ultrasonic (US) friction and interfacial wear in wire bonding. Another objective of the thesis is to develop a low-stress Cu ball bonding process that minimizes damage to the microchip. These are accomplished through experimental measurements of in situ US tangential force by piezoresistive microsensors integrated next to the bonding zone using standard complementary metal oxide semiconductor (CMOS) technology. The processes investigated are thermosonic (TS) Au ball bonding on Al pads (Au-Al process), TS Cu ball bonding on Al pads (Cu-Al process), and US Al wedge-wedge bonding on Al pads (Al-Al process). TS ball bonding processes are optimized with one Au and two Cu wire types, obtaining average shear strength (SS) of more than 120 MPa. Ball bonds made with Cu wire show at least 15% higher SS than those made with Au wire. However, 30% higher US force induced to the bonding pad is measured for the Cu process using the microsensor, which increases the risk of underpad damage. The US force can be reduced by: (i) using a Cu wire type that produces softer deformed ball results in a measured US force reduction of 5%; and (ii) reducing the US level to 0.9 times the conventionally optimized level, the US force can be reduced by 9%. It is shown that using a softer Cu deformed ball and a reduced US level reduces the extra stress observed with Cu wire compared to Au wire by 42%. To study the combined effect of bond force (BF) and US in Cu ball bonding, the US parameter is optimized for eight levels of BF. For ball bonds made with conventionally optimized BF and US settings, the SS is ≈ 140 MPa. The amount of Al pad splash extruding out of bonded ball interface (for conventionally optimized BF and US settings) is between 10–12 µm. It can be reduced to 3–7 µm if accepting a SS reduction to 50–70 MPa. For excessive US settings, elliptical shaped Cu bonded balls are observed, with the major axis perpendicular to the US direction. By using a lower value of BF combined with a reduced US level, the US force can be reduced by 30% while achieving an average SS of at least 120 MPa. These process settings also aid in reducing the amount of splash by 4.3 µm. The US force measurement is like a signature of the bond as it allows for detailed insight into the tribological mechanisms during the bonding process. The relative amount of the third harmonic of US force in the Cu-Al process is found to be five times smaller than in the Au-Al process. In contrast, in the Al-Al process, a large second harmonic content is observed, describing a non-symmetric deviation of the force signal waveform from the sinusoidal shape. This deviation might be due to the reduced geometrical symmetry of the wedge tool. The analysis of harmonics of the US force indicates that although slightly different from each other, stick-slip friction is an important mechanism in all these wire bonding variants. A friction power theory is used to derive the US friction power during Au-Al, Cu-Al, and Al-Al processes. Auxiliary measurements include the current delivered to the US transducer, the vibration amplitude of the bonding tool tip in free-air, and the US tangential force acting on the bonding pad. For bonds made with typical process parameters, several characteristic values used in the friction power model such as the ultrasonic compliance of the bonding system and the profile of the relative interfacial sliding amplitude are determined. The maximum interfacial friction power during Al-Al process is at least 11.5 mW (3.9 W/mm²), which is only about 4.8% of the total electrical power delivered to the US transducer. The total sliding friction energy delivered to the Al-Al wedge bond is 60.4 mJ (20.4 J/mm²). For the Au-Al and Cu-Al processes, the US friction power is derived with an improved, more accurate method to derive the US compliance. The method uses a multi-step bonding process. In the first two steps, the US current is set to levels that are low enough to prevent sliding. Sliding and bonding take place during the third step, when the current is ramped up to the optimum value. The US compliance values are derived from the first two steps. The average maximum interfacial friction power is 10.3 mW (10.8 W/mm²) and 16.9 mW (18.7 W/mm²) for the Au-Al and Cu-Al processes, respectively. The total sliding friction energy delivered to the bond is 48.5 mJ (50.3 J/mm²) and 49.4 mJ (54.8 J/mm²) for the Au-Al and Cu-Al processes, respectively. Finally, the sliding wear theory is used to derive the amount of interfacial wear during Au-Al and Cu-Al processes. The method uses the US force and the derived interfacial sliding amplitude as the main inputs. The estimated total average depth of interfacial wear in Au-Al and Cu-Al processes is 416 nm and 895 nm, respectively. However, the error of estimation of wear in both the Au-Al and the Cu-Al processes is ≈ 50%, making this method less accurate than the friction power and energy results. Given the error in the determination of compliance in the Al-Al process, the error in the estimation of wear in the Al-Al process might have been even larger; hence the wear results pertaining to the Al-Al process are not discussed in this study.

The goal of this thesis is on improving the understanding of mechanical and tribological mechanisms in microelectronic wire bonding. In particular, it focusses on the development and application of quantitative models of ultrasonic (US) friction and interfacial wear in wire bonding. Another objective of the thesis is to develop a low-stress Cu ball bonding process that minimizes damage to the microchip. These are accomplished through experimental measurements of in situ US tangential force by piezoresistive microsensors integrated next to the bonding zone using standard complementary metal oxide semiconductor (CMOS) technology. The processes investigated are thermosonic (TS) Au ball bonding on Al pads (Au-Al process), TS Cu ball bonding on Al pads (Cu-Al process), and US Al wedge-wedge bonding on Al pads (Al-Al process). TS ball bonding processes are optimized with one Au and two Cu wire types, obtaining average shear strength (SS) of more than 120 MPa. Ball bonds made with Cu wire show at least 15% higher SS than those made with Au wire. However, 30% higher US force induced to the bonding pad is measured for the Cu process using the microsensor, which increases the risk of underpad damage. The US force can be reduced by: (i) using a Cu wire type that produces softer deformed ball results in a measured US force reduction of 5%; and (ii) reducing the US level to 0.9 times the conventionally optimized level, the US force can be reduced by 9%. It is shown that using a softer Cu deformed ball and a reduced US level reduces the extra stress observed with Cu wire compared to Au wire by 42%. To study the combined effect of bond force (BF) and US in Cu ball bonding, the US parameter is optimized for eight levels of BF. For ball bonds made with conventionally optimized BF and US settings, the SS is ≈ 140 MPa. The amount of Al pad splash extruding out of bonded ball interface (for conventionally optimized BF and US settings) is between 10–12 µm. It can be reduced to 3–7 µm if accepting a SS reduction to 50–70 MPa. For excessive US settings, elliptical shaped Cu bonded balls are observed, with the major axis perpendicular to the US direction. By using a lower value of BF combined with a reduced US level, the US force can be reduced by 30% while achieving an average SS of at least 120 MPa. These process settings also aid in reducing the amount of splash by 4.3 µm. The US force measurement is like a signature of the bond as it allows for detailed insight into the tribological mechanisms during the bonding process. The relative amount of the third harmonic of US force in the Cu-Al process is found to be five times smaller than in the Au-Al process. In contrast, in the Al-Al process, a large second harmonic content is observed, describing a non-symmetric deviation of the force signal waveform from the sinusoidal shape. This deviation might be due to the reduced geometrical symmetry of the wedge tool. The analysis of harmonics of the US force indicates that although slightly different from each other, stick-slip friction is an important mechanism in all these wire bonding variants. A friction power theory is used to derive the US friction power during Au-Al, Cu-Al, and Al-Al processes. Auxiliary measurements include the current delivered to the US transducer, the vibration amplitude of the bonding tool tip in free-air, and the US tangential force acting on the bonding pad. For bonds made with typical process parameters, several characteristic values used in the friction power model such as the ultrasonic compliance of the bonding system and the profile of the relative interfacial sliding amplitude are determined. The maximum interfacial friction power during Al-Al process is at least 11.5 mW (3.9 W/mm²), which is only about 4.8% of the total electrical power delivered to the US transducer. The total sliding friction energy delivered to the Al-Al wedge bond is 60.4 mJ (20.4 J/mm²). For the Au-Al and Cu-Al processes, the US friction power is derived with an improved, more accurate method to derive the US compliance. The method uses a multi-step bonding process. In the first two steps, the US current is set to levels that are low enough to prevent sliding. Sliding and bonding take place during the third step, when the current is ramped up to the optimum value. The US compliance values are derived from the first two steps. The average maximum interfacial friction power is 10.3 mW (10.8 W/mm²) and 16.9 mW (18.7 W/mm²) for the Au-Al and Cu-Al processes, respectively. The total sliding friction energy delivered to the bond is 48.5 mJ (50.3 J/mm²) and 49.4 mJ (54.8 J/mm²) for the Au-Al and Cu-Al processes, respectively. Finally, the sliding wear theory is used to derive the amount of interfacial wear during Au-Al and Cu-Al processes. The method uses the US force and the derived interfacial sliding amplitude as the main inputs. The estimated total average depth of interfacial wear in Au-Al and Cu-Al processes is 416 nm and 895 nm, respectively. However, the error of estimation of wear in both the Au-Al and the Cu-Al processes is ≈ 50%, making this method less accurate than the friction power and energy results. Given the error in the determination of compliance in the Al-Al process, the error in the estimation of wear in the Al-Al process might have been even larger; hence the wear results pertaining to the Al-Al process are not discussed in this study.

This research conducts tribological investigation in three areas. The first area of research is to obtain basic understanding of tribological properties of high performance Inconel alloys. Pin-on-disk testing was conducted through a range of applied normal loads and sliding velocities in an unlubricated condition. Average friction coefficient, friction work, and specific wear rates were calculated from the data and microscopy techniques were used to observe and characterize wear mechanisms. Experimental results show a dependence of average coefficient of friction as a function of frictional work. Also shown is the wear rate dependence on frictional work, predicated by a wear mechanism change. This research gives a tribological baseline for high performance alloys. The second area of research is in the in situ spatial study of friction, complemented by monitoring changes in electrical contact resistance (ECR). Pin-on-disk testing of samples was done under low normal loads and velocities. Friction and electrical contact resistance measurements were taken spatially in the wear track during each friction cycle, giving a spatial evolution of friction and resistance change, in situ. Results show a lowering in the ECR under increased friction cycles, which was closely related to a change in the friction coefficient of the material. Using surface profilometry and X-ray Photoelectron Spectroscopy, we determined that the lowering of resistance is a result of surface modification through wear and development of a friction induced conductive tribo-film. This research provides a simple method for in situ monitoring of friction and solidifies a fundamental relationship between friction and contact resistance. The third area of research is the design of a variable force tribometer, incorporating the fundamental results demonstrated in the first two experiments. The creation of a novel testing apparatus to test materials under dynamic tribological conditions is given in detail. Simple experiments were performed on an Inconel sample and preliminary results show how dynamic normal and tangential forces affect the friction coefficient. These early results utilizing the variable force tribometer will lay the groundwork for more advanced research into the dynamic nature of friction.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Grease-lubricated journal bearings are widely used in heavy duty applications, such as construction equipment, agriculture- and forest machines. The main purpose of the grease-lubricated journal bearing is solely to create sustainable rotation of a given application. However, purpose seldom decides complexity of journal bearing design. Depending on application, parameters such as Load , Material  and Lubrication immensely increase complexity of the design. Tribology is a highly interdisciplinary subject, which requires knowledge concerning physics, chemistry, metallurgy and solid mechanics. Tribological aspects of a design are frequently regarded as irrelevant. Tribological issues are commonly enlightened in combination with structural design weaknesses. The main aim of the thesis was to analyze two cylinder joints found in a Komatsu Forest 951 crane and establish root cause to the structural and tribological issues. Outline of the approach was divided into three main targets: 1. Investigate mechanical and tribological aspects of the crane design. 2. Understand how these aspects influence the life time of the bearings. 3. Summarize the analysis and suggest improvements based on the discovery. Fundamental structural and tribological design guidelines regarding grease-lubricated journal bearings have been presented in this thesis. Damaged components such as cylinders, pins and journal bearings have been examined at Komatsu Forest’s factory in Umeå. Further, a scanning electron microscopy study has been done at Luleå University of Technology, to determine predominant wear mechanisms in the harvester crane joints. A non-linear finite element model of the crane has been designed to represent pressure distribution in the contact between bearing and pin. The finite element analysis gives a good approximation of the contact but leaves room for further refinements. Temperatures, in the contacts, have not been identified and will be measured outside the time frame of the master’s thesis. Design changes, with respect to discovered structural and tribological issues have been suggested. The suggested improvements can potentially increase the life time of lift cylinders, pins and journal bearings.

Aços inoxidáveis duplex (AID) são materiais amplamente utilizados para uma grande variedade de aplicações desde a indústria química, de alimentos, petroquímica, naval, farmacêutica, energia nuclear e em muitos outros campos devido à combinação de suas excelentes propriedades mecânicas e de resistência à corrosão. Particularmente na indústria petroquímica, os aços AID’s são muito utilizados como materiais estruturais para a construção de gasodutos que transportam altos volumes de CO2 e na confecção das camadas internas dos tubos flexíveis (oleodutos offshore), utilizadas na produção de óleo. A soldagem a arco dos AID’s pode acarretar, dependendo das taxas de resfriamento envolvidas, a formação de precipitados de segunda fase que degradam suas propriedades mecânicas. Um processo alternativo para evitar o problema de precipitação de fases indesejáveis é a utilização do processo de soldagem/reparo por fricção com pino consumível (SFPC). O objetivo do presente trabalho é a caracterização metalúrgica e mecânica de juntas de solda de aço inoxidável duplex UNS S31803 obtidas através dos processos SFPC e de soldagem de costura por fricção (SCF). Na soldagem SCF, o objetivo do estudo foi a verificação da influência do passo de soldagem na formação e alteração das estruturas e nas propriedades mecânicas. Os resultados dos ensaios foram comparados com as propriedades obtidas do material base (MB) “como recebido”. A partir das juntas soldadas obtidas por fricção, foram extraídos corpos de prova para ensaios de microtração e Charpy para avaliação da resistência mecânica e da resistência ao impacto. Análises da microestrutura em microscopia ótica (MO) e perfis de microdurezas ao longo da região de solda também foram realizadas. Verificou-se que os processos de soldagem SFPC e SCF provocam um intenso refinamento de grão na zona de mistura (região da interface entre material do pino e da base), modificando a estrutura lamelar de grãos alongados da matriz ferrítica/austenítica, ocasionado por uma ação conjunta de aquecimento e deformação plástica oriunda do processo de solda por fricção. Os resultados dos ensaios de microtração indicam que as juntas soldadas aumentaram sua resistência mecânica com relação ao material base, fato que se deve ao aumento da quantidade da ferrita na zona termomecanicamente afetada (ZTMA), à formação de nitretos de cromo no centro dos grãos ferríticos e ao refino de grão. O aumento da quantidade de ferrita na ZTMA ocorre devido às altas taxas de resfriamento envolvidas no processo de soldagem e verificados por análise térmica. As elevadas taxas de resfriamento dificultam a difusão do nitrogênio que tem um importante papel no equilíbrio de fases da estrutura duplex (ferrita-austenita), na soldagem. O nitrogênio aprisionado no interior do grão ferrítico produz nitretos de cromo deixando de agir como elemento gamagênico aumentando a quantidade da fase ferrita. As juntas soldadas verificadas apresentaram tenacidade aceitável de acordo com o exigido pela norma ASTM A923. / Duplex stainless steels (DSS) are materials widely used for a variety of applications from the chemical, food, petrochemical, marine, pharmaceutical, nuclear industry and other fields due to the combination of their excellent mechanical properties and corrosion resistance. Particularly in the petrochemical industry, the DSS’s steels are extensively used as structural materials for the construction of gas pipelines that carry high volumes of CO2 and making the inner layers of flexible pipes (pipelines offshore) used in offshore oil production. The arc welding of DSS's can lead, depending on cooling rates involved, the formation of second phase precipitates which degrade their mechanical properties. An alternative method to avoid the problem of precipitation of unwanted phase is to use the welding process Friction Hydro Pillar Processing (FHPP). The aim of this work is the metallurgical and mechanical characterization of joints welds of UNS S31803 duplex stainless steel obtained through FHPP processes and Friction Taper Stitch Welding (FTSW). In FTSW welding, the objective of the study was to verify the influence of the welding step on the formation and alteration of structures and mechanical properties. The test results were compared with the properties of the obtained base material "as received". From the welds joints obtained by friction welding, specimens for microtensile testing and charpy were extracted to evaluate the mechanical strength and toughness. Microstructural analysis in optical microscopy (OM) and scanning electron microscopy (SEM) and microhardness profiles along the weld region were also performed. It was found that the welding process FHPP and FTSW causes an intense grain refinement in bonding zone, modifying the lamellar structure of elongate grains of matrix ferritic/austenitic, caused by action of heating and plastic deformation arising from the welding process by friction. The results of the microtensile tests indicate that the welded joints increased their mechanical resistance with respect to the base material, due to the increase in the amount of the ferrite in the thermomechanically affected zone (ZTMA), the formation of chromium nitrides in the center of ferritic grains and grain refining. The increase in the amount of ferrite in the ZTMA occurs due to the high cooling rates involved in the welding process and verified by thermal analysis. The high cooling rates difficult the nitrogen diffusion, which plays an important role in the phase equilibrium of the duplex structure (ferrite-austenite) in welding. The nitrogen trapped inside the ferritic grain produces chromium nitrides ceasing to act as gamogenic element by increasing the amount of the ferrite phase. The welds joints verified also had acceptable ductility and toughness according required by standard ASTM A923.

This thesis summarizes the work done on tribological characterization of multifunctional hardfacing coatings with self-lubricating properties, intended for use in mechanical components operating in high temperature applications for which conventional lubricants are no longer effective. Deposition techniques like laser cladding have a great potential in reworking/repair of high value industrial components in order to extend their lifetime. It is expected that the use of self-lubricating laser claddings could be useful in high temperature applications like metal forming, leading to decreased friction and wear. In this study, the tribological behavior of self-lubricating claddings has been studied against steel and aluminum counter surfaces, using ASI52100 bearing steel in addition to AA6082 and AA2007 aluminum flat pins as the counter bodies. Nickel- and iron-based powders have been chosen for the preparation of claddings. Self-lubricating properties of Ag/MoS2 have been compared to an untreated reference cladding and grade 1.2367 tool steel. For steel counter surfaces, tribological properties in the temperature range between RT and 600⁰C have been investigated and at 300°C for aluminum counter surfaces. Tribological tests were done by a high frequency linear oscillation (SRV) test machine under reciprocating conditions. The wear scar and volume of coatings were measured by using a 3D optical profilometer. SEM/EDS analysis were additionally performed for the characterization of microstructure and wear scar. The results indicated that MoS2 reduced friction and wear of the Fe-based cladding material when tested against steel at room temperature compared to the reference alloy and grade 1.2367 tool steel, and that the addition of silver further decreased wear in addition to early stage friction. It was also observed that the tribolayer, which was formed during the sliding of Ni-based - 5 Ag - 10 MoS2 and against aluminium under lubricated conditions, was protective and provided low and steady friction.

Les technologies actuellement utilisées pour les moteurs diesel conduisent à la dégradation accélérée des constituants chimiques des lubrifiants, notamment des additifs non polymériques de type antioxydants, anti-usures, modificateurs de friction et de détergence.Nos travaux visent à identifier la nature des modifications chimiques de ces additifs au cours du fonctionnement moteur. Ainsi, un protocole analytique a été établi afin d’étudier qualitativement et quantitativement ces familles dans les lubrifiants.Ce protocole a ensuite été utilisé pour l’analyse d’huiles vieillies lors de tests sur banc moteur et d’essais réalisés en laboratoire. L'évolution de la composition chimique des lubrifiants, la nature des produits de dégradation formés, et les processus d'altération impliqués ont ainsi été étudiés, et des modèles cinétiques de la dégradation de chaque famille d’additifs ont été établis.Il ressort de notre étude que les processus mis en jeu dans l’altération des additifs en laboratoire ne reproduisent pas ceux existant lors du fonctionnement moteur, ce qui laisse envisager le développement d'expériences de laboratoire mieux adaptées. / Current technologies used for diesel engines lead to an accelerated degradation of the non-polymeric additives from lubricants, such as antioxidants, antiwear, friction modifiers and detergency additives.Our work intends to identify the nature of the chemical modifications undergone by such additives during engine functioning. In this respect, an analytical protocol has been developed in order to investigate qualitatively and quantitatively these compound families in engine oils. Following this, the analytical methodology has then been used to study oils altered during engine bench tests and laboratory experiments. Thus, the evolution of the chemical composition, the nature of the degradation products and the alteration processes have been considered. Furthermore, kinetic models have been established for each family of additives.It appears from this study that the processes implied in the alteration of the additives during laboratory tests do not reproduce those existing while engine running. Further laboratory experiments are needed in order to develop tests mimicking more closely the conditions occurring during engine functioning.

Le soudage par friction (Friction Stir Welding - FSW) est un processus efficace de se joindre des alliages d'aluminium à haute résistance en évitant les défauts que l'on trouve habituellement lorsque les techniques de soudage classiques sont utilisés. L'industrie de l'aviation a montré un grand intérêt pour cette méthode de soudage, tant pour l'union des alliages semblables comme pour dissemblables. Cependant, ce processus entraîne des changements de microstructure dépendantes des conditions de traitement thermique ou thermomécanique. Le contact électrique entre les différentes zones de microstructures, à son tour, peut conduire à un couplage galvanique entre les différentes zones. Dans la présente étude, le soudage FSW a été utilisé pour joindre deux alliages d'aluminium dissemblables,AA2024-T3 et AA7475-T651. La résistance à la corrosion des joints soudés a été évaluée par des tests électrochimiques, en particulier, les mesures de potentiel en circuit ouvert(OCP), les courbes de polarisation, et des mesures de spectroscopie d'impédance électrochimique, soit globale (EIS) ou local (LEIS) en solution de 0,1 M Na2SO4 ou 0,1MNa2SO4 + 1 mM NaCl. Les tests électrochimiques ont montré l'effet de couplage galvanique dans les joints soudés. La résistance à la corrosion intergranulaires et la résistance à corrosion par exfoliation des joints soudés ont également été évaluées et comparées à celles du AA2024-T3 et les alliages AA7475-T651 non soudées. Les résultats ont montré une réactivité accrue des joints soudés en comparaison avec les alliages non soudés en notant l'attaque plus intense sur l'alliage AA7475-T651. L'identification des zones cathodiques et anodiques dans les joints soudées ont été évaluée par un test consistant à déposer un gel(agar) avec l'indicateur universel et il a été observé que l'alliage AA2024-T3 a agi en tant que cathode, tandis que la AA7475- T651 comme anode. Par ailleurs, le dégagement d'hydrogène a été observée dans la région d'interface entre la zone affectée thermomécaniquement et l'alliage AA7475-T651 affectée par la chaleur. Les résultats des essais de LEIS effectuées dans différentes zones des deux alliages soudés par FSW ont montré l'engagement galvanique à l'interface entre eux pour de courtes durées d'analyse etde déplacement de la région la plus active dans le temps de test pour l'alliage AA7475-T651,plus précisément à l'interface entre la zone affectée thermomécaniquement et la thérmique affectée de cette alliage. / 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 processon 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) orlocal (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 tothe 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 theAA7475-T651 alloy, at longer periods of test, specifically to the interface between the thermomechanically affected and the heat affected zones of this last alloy. / A soldagem por fricção (Friction Stir Welding - FSW) é um processo eficiente de unir ligas dealumínio de alta resistência evitando defeitos que são usualmente criados quando técnicasconvencionais de soldagem são utilizadas. A indústria aeronáutica tem mostrado grande interesseneste método de soldagem, tanto para a união de ligas similares como dissimilares. Entretanto,este processo causa modificações microestruturais dependentes das condições de tratamentotérmico 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 paraunir duas ligas de alumínio dissimilares, AA2024-T3 e AA7475-T651 e o efeito desta soldagem naresistência à corrosão das juntas soldadas e na microestrutura das ligas foi avaliada. Nainvestigação 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 ensaioseletroquímicos evidenciaram efeito de acoplamento galvânico nas juntas soldadas. Acaracterização microestrutural foi realizada por microscopia ótica, microscopia eletrônica devarredura, microscopia eletrônica de transmissão e por calorimetria diferencial. As zonas afetadaspela solda tiveram importantes modificações na microestrutura indicadas pela precipitação edissolução de precipitados que afetam a resistência à corrosão localizada. A resistência à corrosãointergranular e a resistência à esfoliação das juntas soldadas também foram avaliadas ecomparadas com as das ligas AA2024-T3 e AA7475-T651 não soldadas. Os resultados mostraramaumento da suscetibilidade das juntas soldadas a estas formas de corrosão em comparação comas ligas não soldadas sendo observado ataque mais severo na liga AA7475-T651. A identificaçãodas áreas anódicas e catódicas resultantes do acoplamento galvânico nas juntas soldadas foirealizada por teste que consistiu na deposição de camada de gel (ágar-ágar) com indicadoruniversal na superfície das ligas soldadas. A liga AA2024-T3 atuou como cátodo, enquanto aAA7475-T651, como ânodo no par galvânico. Além disso, evolução de hidrogênio foi observada naregião de interface entre a zona termomecanicamente afetada e a termicamente afetada da ligaAA7475-T651 mostrando que reações catódicas também ocorreram localmente nesta última liga.Resultados de LEIS obtidos nas diferentes zonas das duas ligas soldadas por FSW mostraramacoplamento galvânico na interface entre elas para tempos curtos de ensaio e deslocamento daregião mais ativa com o tempo de ensaio para a liga AA7475-T651, mais precisamente para ainterface entre a zona termomecanicamente afetada e a térmicamente afetada desta liga.