Friction stir welding has become a popular forging technique used in many applications. The Swedish Nuclear Fuel and Waste Management Company (SKB) evaluates this method to seal the 5 cm thick copper canisters that will contain the spent nuclear fuel. To produce repetitive, high quality welds, the process must be controlled, and today a cascade controller is used to keep the desired stir zone temperature. In this thesis, the control system is extended to also include a plunge depth controller. Two different approaches are evaluated; the first attempt is a decentralized solution where the cascaded temperature controller is kept, and the second approach uses a non-linear model predictive controller for both depth and temperature. Suitable models have been derived and used to design the controllers; a simpler model for the decentralized control and a more extensive, full model used in the non-linear model predictive controller that relates all the important process variables. The two controller designs are compared according to important performance measures, and the achieved increase in performance with the more complex non-linear model predictive controller is evaluated. The non-linear model predictive controller has not been implemented on the real process. Hence, simulations of the closed loop systems using the full model have been used to compare and evaluate the control strategies. The decentralized controller has been implemented on the real system. Two welds have been made using plunge depth control with excellent experimental results, confirming that the decentralized controller design proposed in this thesis can be successfully used. Even though the controller manages to regulate the plunge depth with satisfying performance, simulations indicate that the non-linear model predictive controller achieves even better closed loop performance. This controller manages to compensate for the cross-connections between the process variables, and the resulting closed loop system is almost decoupled. Further research will reveal which control design that will finally be used. / ''Friction stir welding'' har blivit en populär svetsmetod inom många olika tillämpningar. På Svensk Kärnbränslehantering AB (SKB) undersöks möjligheten att använda metoden för att försegla de 5 cm tjocka kopparkapslarna som kommer innehålla det använda kärnbränslet. För att kunna producera repeterbara svetsar utav hög kvalité krävs det att processen regleras. Idag löses detta med en temperaturregulator som reglerar svetszonens temperatur. I detta examensarbete utökas styrsystemet med en regulator för svetsdjupet. Två olika lösningar har utvärderats; först en decentraliserad lösning där temperatur-regulatorn behålls och sedan en lösning med en olinjär modellprediktiv reglering (MPC) som reglerar både djup och temperatur. Passande modeller har tagits fram och har använts för att designa regulatorerna; en enklare modell för den decentraliserade regulatorn och en utökad, komplett modell som används i den olinjära MPC:n och som beskriver alla viktiga variabler i processen. Viktiga prestandamått har jämförts för de båda regulatorstrukturerna och även prestandaökningen med den olinjära MPC:n har utvärderats. Då denna regulator inte har implementerats på den verkliga processen har simuleringar av den kompletta modellen använts för att jämföra och utvärdera regulatorstrukturerna. Den decentraliserade regulatorn har implementerats och testats på processen. Två svetsar har gjorts och de har givit utmärkta resultat, vilket visar att regulatorstrukturen som presenteras i rapporten fungerar bra för reglering av svetsdjupet. Trots att den implementerade regulatorn klarar av att reglera svetsdjupet med godkänt resultat, så visar simuleringar att den olinjära MPC:n ger ännu bättre reglerprestanda. Denna regulator kompenserar för korskopplingar i systemet och resulterar i ett slutet system som är nästan helt frikopplat. Ytterligare forskning kommer avgöra vilken av strategierna som kommer att användas i slutprodukten.

Friction Stir Welding (FSW) is an emerging solid state welding process. It has been a proven method for welding high strength aluminium alloys which were previously not recommended for conventional fusion welding. Since the invention of the process by The Welding Institute, United Kingdom, in 1991, a number of studies have been conducted on the material flow, microstructural evolution and mechanical properties of friction stir welds. However, there is not enough conceptual background available on FSW process for physical understanding of the mechanism of weld formation. In addition to that, FSW welds of high strength precipitation hardenable aluminium alloys suffer from reduced joint efficiency due to overaging in the heat affected zone. In the present investigation, experimental analysis has been carried out to understand the mechanism of weld formation and parameter optimization for aluminium alloys 7020-T6 and 6061-T6. For this purpose the investigations have been made on both the process aspects and the material aspects. The process aspects are analyzed with the objective of learning the mechanism to produce defect free welds. For this purpose experiments have been carried out to analyze the effect of FSW parameters, material flow and the frictional characteristics between the tool and base metal. Preliminary experiments are conducted on aluminium alloy 7020-T6 with different tool geometries to analyze the interaction of the tool with the base metal using a knee-type vertical milling machine. Then, the tool geometry which produced defect-free weld is used for further experimentation. The role of tool pin, shoulder and axial load on the formation of defect free weld is analyzed in an innovative experiment, where the tool and base metal interaction is continuously increased by continuously increasing the interference between the tool and base metal. In another experiment the initial abutting interface position with respect to the tool is continuously varied to study the interaction of the tool with the initial interface and to find the positional information where the initial interface is completely eliminated. Further, the tool metal interface condition is studied using a specially designed tribological experiment which simulates the FSW condition. From the base metal point of view, due to the strain, strain rate and temperature imposed on the base metal during the process, the microstructure is altered. In precipitation hardenable aluminium alloys the strengthening precipitates are dissolved or overaged in the weld region depending on the peak temperature in the region, which reduces the joint efficiency. However, the dissolution and overaging are kinetic process. In order to analyze this time dependant softening behavior of the base metal 7020-T6 and 6061-T6, isothermal annealing and differential scanning calorimetric studies are performed. In order to obtain FSW welds with maximum joint efficiency, the welding temperature should not exceed the “softening temperature” of the base metal. But, to produce defect free welds favorable material flow in the weld nugget is necessary. The material flow and consolidation depend on the process temperature. Hence, for a given tool to produce defect free weld there is a need for minimum temperature. If the weld formation temperature is less than the base metal softening temperature, the weld can be made with 100% joint efficiency. In order to optimize the FSW parameter which gives defect free weld with lowest possible temperature, an instrumented programmable FSW machine is designed and developed. The machine is designed in such a way that welding parameters – rotation speed, traverse speed and plunging depth – can be continuously varied from the start to end of the weld between given two values. This reduces the number of experimental trials, material and time. Based on the experimental results the following conclusions are derived. 1.The minimum diameter of the pin required for FSW depends on the base metal and tool material property for a given set of parameters. If the pin diameter is insufficient for a given set of welding parameters, it fails during plunging operation itself. 2.There is a minimum diameter of the shoulder for a given diameter of the pin which produces defect free weld. The ratio of pin to shoulder to produce a defect free weld is not a constant value. It changes with tool geometry and process parameters. 3.Increasing the area of contact between the tool and shoulder for a given set of parameters increases the heat input and results in increased weld nugget grain size. 4.Initial abutting interface of the base metal is eliminated at the leading edge of the tool. However, new surfaces are generated due to interaction with the tool and the newer surfaces are consolidated at the trailing edge of the tool. Importantly, the weld strength is controlled by the defects generated due the improper elimination of newly generated surfaces. 5.Optimal axial load is required to generate the required pressure to consolidate the transferred material at the trailing edge of the tool and should be equal to the flow stress of the material at the processing temperature. The optimal axial load is 8.1kN for a tool having 20mm diameter shoulder with 6mm diameter frustum shaped pin. 6.Only the material that approaches the tool at the leading edge on the advancing side is stirred and the remaining material is simply extruded around the tool. Further, the initial abutting interface is completely removed only when it is located in the stirring zone, otherwise the initial abutting interface is not eliminated. In the present study the interface is completely stirred when it is located on the advancing side of the tool between 0.5mm away from the centerline and edge of the tool. 7.The temperature and pressure at the tool–base metal interface is above the temperature and pressure required for seizure to occur for given tool material (H13) and base metal (7020-T6). Hence, it is clear that during FSW the base metal transfers on to the tool and interaction occurs between transferred layer on tool and base metal. The coefficient of friction between the given tool material and base metal in FSW condition is in the range of 1.2 – 1.4. 8.The minimum temperature requirement for FSW of 7020-T6 is 400oC and 6061-T6 is 430oC. However, 7020-T6 and 6061-T6 softens at lower temperatures than that of the minimum FSW temperature. 7020-T6 softens 30% in 7min at 250oC, 4min at 300oC, 2min at 350oC and 1min at 400oC. After softening 30%, there is 10% recovery in hardness and the hardness remains constant thereafter. Whereas 6061-T6 softens gradually up to 47% in 7min at 350oC and 400oC, below the temperature of 250oC for 7020-T6 and 350oC for 6061-T6 there is no softening observed in 7min. 9.The maximum joint efficiency of the 7020-T6 weld is 82% and 6061-T6 weld is 60%. 10. The reduction in joint efficiency is attributed to overaging of the material in the heat affected zone.

<p>The Swedish model for final disposal of nuclear fuel waste is based on copper canisters as a corrosion barrier with an inner pressure holding insert of cast iron. One of the methods to seal the copper canister is to use the Friction Stir Welding (FSW), a method invented by The Welding Institute (TWI).</p><p>This work has been focused on characterisation of the FSW joints, and modelling of the process, both analytically and numerically. The first simulations were based on Rosenthal’s analytical medium plate model. The model is simple to use, but has limitations. Finite element models were developed, initially with a two-dimensional geometry. Due to the requirements of describing both the heat flow and the tool movement, three-dimensional models were developed. These models take into account heat transfer, material flow, and continuum mechanics. The geometries of the models are based on the simulation experiments carried out at TWI and at Swedish Nuclear Fuel Waste and Management Co (SKB). Temperature distribution, material flow and their effects on the thermal expansion were predicted for a full-scale canister and lid. The steady state solutions have been compared with temperature measurements, showing good agreement.</p><p>Microstructure and hardness profiles have been investigated by optical microscope, Scanning Electron Microscope (SEM), Electron Back Scatter Diffraction (EBSD) and Rockwell hardness measurements. EBSD visualisation has been used to determine the grain size distribution and the appearance of twins and misorientation within grains. The orientation maps show a fine uniform equiaxed grain structure. The root of the weld exhibits the smallest grains and many annealing twins. This may be due to deformation after recrystallisation. The appearance of the nugget and the grain size depends on the position of the weld. A large difference can be seen both in hardness and grain size between the start of the weld and when the steady state is reached.</p>

This thesis presents results from the application of cryogenic cooling on multiple-pass friction stir processing and the subsequent orthogonal machining on friction stir processed and as-received Mg AZ31B-O disks, and shows their combined effects on microstructure and microhardness values. A simple friction stir tool, a specially designed fixture and liquid nitrogen are used to perform multiple-pass friction stir processing experiments on Mg AZ31B-O alloy. The friction stir processed and as-received sheets are then made into disks for the orthogonal machining experiments. This study analyzes the microhardness, microstructure changes by cryogenic friction stir processing and the effect of machining conditions such as dry, MQL and cryogenic and cutting parameters on the Mg AZ31B-O alloy. Four different speeds and three different feed rates are used for the orthogonal machining experiments. The effects of stirring parameters such as the translational feed, rotational speed, cooling conditions and the machining parameters are studied. The resulting microstructure and microhardness from these processes hold a key to the mechanical properties of the alloy. This analysis would help to understand and evaluate the specific aspects of grain size and microhardness that influence the fatigue life of a component.

As ligas de alumínio AA2024 e AA7050 tradicionalmente são utilizadas na fabricação de estruturas da fuselagem e da asa de aeronaves. Normalmente, a união dos componentes dessas estruturas é realizada por rebites, já que processos de soldagem com fusão produziriam defeitos indesejáveis. O processo de soldagem por fricção linear com mistura ou Friction Stir Welding (FSW) é uma alternativa à união de chapas de ligas de alumínio por rebites haja vista que não há fusão do material durante a união. No presente trabalho estudou-se o comportamento eletroquímico e a caracterização microestrutural de uma junta sobreposta, composta por um perfil extrudado da liga AA7050-T76511 e uma chapa da liga AA2024-T3, ambos previamente anodizados, soldada por fricção linear com mistura. O comportamento eletroquímico foi avaliado através da utilização da Técnica de Varredura com Eletrodo Vibratório (SVET), medidas do potencial de corrosão e curvas de voltametria cíclica em solução de 0,1 M de NaCl. Correntes anódicas mais intensas foram medidas na região da solda e ainda verificou-se que esta possui menores potenciais de pite e corrosão do que ambas as ligas. Também foi constatada a presença de corrosão intercristalina em ambas as ligas e na região da solda, porém com maior severidade na liga AA2024-T3. / AA2024 and AA7050 aluminum alloys are traditionally used in the manufacture of fuselage structures and aircrafts wings. Usually, the component union of these structures is made using rivets since weld process with melting will produce unwanted defects. The Friction Stir Welding (FSW) process is an alternative way to replace the traditional rivet union of aluminum alloys in the aeronautical and aerospace industries since the material does not melt during the joint. In the present work it has been studied the electrochemical behavior and microstructural characterization of a lap joint composed of an extruded profile of AA7050-T76511 alloy and a sheet of AA2024-T3 alloy, both of them previously anodized and jointed by friction stir welding. The electrochemical behavior was evaluated by means of Scanning Vibrating Electrode Technique (SVET), measurements of the corrosion potential and cyclic voltammetry in 0,1 M NaCl. Higher anodic currents were found in the weld region, moreover this region has the lowest pit and corrosion potential. Intercrystalline corrosion was found in both alloys and in the weld region, with the highest intensity in the AA2024-T3 alloy.

Este trabalho apresenta um modelo inovador de coletor solar plano, com placa absorvedora fabricada por Estampagem Incremental e Soldagem FSW (Friction Stir Welding). Esta placa absorvedora é constituída de duas chapas de alumínio AA1200-H14 com espessura de 1 mm, estampadas e soldadas em simetria, a fim de que na união das chapas sejam deixados canais para passagem de água. Neste estudo foi realizada a caracterização do material por Ensaio de Tração e Ensaio Nakajima. Para determinação dos parâmetros de Estampagem Incremental foram realizados 16 experimentos com ferramenta de diâmetro df = 9,5 mm, variando a rotação de N = 50 rpm a 800 rpm e o incremento vertical de Δz = 2 mm a 0,2 mm, mantendo o avanço em = 250 mm/min. E também foram realizados 3 experimentos com ferramenta df = 22 mm, variando o incremento vertical de Δz = 2 mm a 0,5 mm, mantendo a rotação em N = 50 rpm e o avanço em = 250 mm/min. Para determinação dos parâmetros de Soldagem FSW foram realizados 4 experimentos com ferramenta de ombro de diâmetro 8 mm e pino roscado M3x0,5, mantendo a rotação em N = 1500 rpm e variando o avanço entre = 100 mm/min a 400 mm/min. Em seguida foi fabricado um protótipo de placa absorvedora de coletor solar com área de 0,12 m². Nos experimentos realizados foi constatado que é possível obter maiores deformações na Estampagem Incremental do que na Estampagem Convencional e que as deformações são mais elevadas quando se utiliza menores diâmetros, maiores rotações e menores incrementos verticais da ferramenta. Na Soldagem FSW não foi constatada influência na qualidade do cordão de solda em relação à variação do avanço da ferramenta. Neste estudo também se verificou que é possível fabricar protótipos de placas absorvedoras de coletores solares pelos processos de Estampagem Incremental e Soldagem FSW. No entanto, para coletores em tamanho comercial, novos estudos são necessários para melhorar a forma de fixação das chapas durante a Soldagem FSW. / This work presents an innovative model of flat plate solar collector, with absorber plate manufactured using Incremental Sheet Forming (ISF) and Friction Stir Welding (FSW). This absorber plate consists of two AA1200-H14 aluminum sheets with a thickness of 1 mm, stamped and welded in symmetry, in order to leave channels for the passage of water. In this study the characterization of the material by Nakajima Test and Traction Test was performed. In order to determine the parameters of ISF, 16 experiments were performed with a tool of diameter df = 9.5 mm, varying the rotation speed of N = 50 rpm at 800 rpm and the step down of Δz = 2 mm to 0.2 mm, maintaining the feed rate at = 250 mm/min. Also, 3 experiments with tool df = 22 mm were performed, varying the step down of Δz = 2 mm to 0.5 mm, maintaining the rotation speed at N = 50 rpm and the feed rate at = 250 mm/min. For determination of FSW parameters, 4 experiments with 8 mm diameter shoulder tool and M3x0.5 pin were performed, maintaining the rotation speed at N = 1500 rpm and varying the feed rate from = 100 mm/min to 400 mm/min. A prototype solar collector absorber plate with a 0.12 m² area was then manufactured. In the experiments carried out, it was found that it is possible to obtain greater deformations in the ISF than in the Conventional Stamping and that the deformations are higher when using smaller diameters, higher rotations and smaller step downs of the tool. In FSW, no influence was observed in the quality of the weld bead in relation to the variation of the tool feed rate. In this study it was also verified that it is possible to manufacture prototypes of solar collector absorber plates by the processes of ISF and FSW. However, for commercial size collectors, further studies are needed to improve the way the plates are fixed during FSW.

As ligas de alumínio AA2024 e AA7050 tradicionalmente são utilizadas na fabricação de estruturas da fuselagem e da asa de aeronaves. Normalmente, a união dos componentes dessas estruturas é realizada por rebites, já que processos de soldagem com fusão produziriam defeitos indesejáveis. O processo de soldagem por fricção linear com mistura ou Friction Stir Welding (FSW) é uma alternativa à união de chapas de ligas de alumínio por rebites haja vista que não há fusão do material durante a união. No presente trabalho estudou-se o comportamento eletroquímico e a caracterização microestrutural de uma junta sobreposta, composta por um perfil extrudado da liga AA7050-T76511 e uma chapa da liga AA2024-T3, ambos previamente anodizados, soldada por fricção linear com mistura. O comportamento eletroquímico foi avaliado através da utilização da Técnica de Varredura com Eletrodo Vibratório (SVET), medidas do potencial de corrosão e curvas de voltametria cíclica em solução de 0,1 M de NaCl. Correntes anódicas mais intensas foram medidas na região da solda e ainda verificou-se que esta possui menores potenciais de pite e corrosão do que ambas as ligas. Também foi constatada a presença de corrosão intercristalina em ambas as ligas e na região da solda, porém com maior severidade na liga AA2024-T3. / AA2024 and AA7050 aluminum alloys are traditionally used in the manufacture of fuselage structures and aircrafts wings. Usually, the component union of these structures is made using rivets since weld process with melting will produce unwanted defects. The Friction Stir Welding (FSW) process is an alternative way to replace the traditional rivet union of aluminum alloys in the aeronautical and aerospace industries since the material does not melt during the joint. In the present work it has been studied the electrochemical behavior and microstructural characterization of a lap joint composed of an extruded profile of AA7050-T76511 alloy and a sheet of AA2024-T3 alloy, both of them previously anodized and jointed by friction stir welding. The electrochemical behavior was evaluated by means of Scanning Vibrating Electrode Technique (SVET), measurements of the corrosion potential and cyclic voltammetry in 0,1 M NaCl. Higher anodic currents were found in the weld region, moreover this region has the lowest pit and corrosion potential. Intercrystalline corrosion was found in both alloys and in the weld region, with the highest intensity in the AA2024-T3 alloy.

O processo de soldagem por atrito linear com mistura (SALM), ou Friction Stir Welding, surgiu do desejo de se aplicar os princípios e vantagens da soldagem em estado sólido do processo por atrito tradicional em outras geometrias que não fossem axi-simétricas. Assim, foi acrescentada uma velocidade de translação e uma ferramenta rotativa especial, sendo possível realizar cordões de solda em ligas antes com soldabilidade bem ruim. O fator chave para se ter uma solda por atrito linear com mistura sã é a combinação correta entre o a geometria da ferramenta, os parâmetros de soldagem e o fluxo de material durante a soldagem. O lado do avanço, em relação à velocidade de translação da ferramenta, está sob tração, enquanto que o lado do retrocesso está sob compressão. Cada um destes lados possui características diferenciadas, tanto microestruturais como de propriedades mecânicas. O objetivo deste trabalho é caracterizar o cordão de solda feito em liga AA6063T6 com 3 mm de espessura. O material foi soldado com uma ferramenta tipo Three flats, com rotação de 1120 rpm e velocidade de soldagem de 5,3 mm/s. Os corpos de prova foram caracterizados por microscopia óptica, microdureza e ensaio de tração. Os resultados mostraram que o cordão de solda é assimétrico, sendo 20% maior do lado do avanço da ferramenta. Além disto, houve um refino de grão e, na transição entre a zona termomecanicamente afetada (ZTMA) e a zona afetada pelo calor (ZAC), os grãos alongados apresentaram fator de forma maior no lado do avanço (entre 1,73 e 2,74) do que no lado do retrocesso (entre 1,40 e 1,59). As extensões da zona termomecanicamente afetada e da zona afetada pelo calor são maiores do lado do avanço que do lado do retrocesso. / Friction Stir Welding process arose from a desire to apply the principles and benefits of traditional solid state friction welding friction in non axi-symmetric geometries. Thus, it was added a traveling speed and a special rotating tool that allows welding aluminum alloys with bad weldability. The key factor to have a linear friction welding with sound bead is a combination of tool geometry, welding parameters and material flow during welding, which is under tension stress in the advancing side and in compression in the retrieving side. Thus, each side has different microstructures and mechanical properties. The objective of this work is to characterize the 3,0 mm weld bead of an alloy 6063 T6. This material was welded with a tool type \"Three flats\" with a rotation speed of 1120 rpm and welding traveling speed of 5.3 mm/s. The samples were characterized by optical microscopy, microhardness testing and tensile test. The results showed that the weld bead is asymmetric, with an area 20% higher in the advancing side. Moreover, a grain refining process occurred in the weld bead and, in the transition region between thermomechanically affected zone (TMAZ) and heat affected zone (HAZ) the elongated grains presented a shape factor higher in the advancing side (1,73 to 2,74) than in the retrieving side (1,40 to 1,59). Also, the thermomechanically affected zone and the heat affected zone presented a larger width in the advancing side than in the retrieving side.

As ligas de alumínio AA2024 e AA7050 tradicionalmente são utilizadas na fabricação de estruturas da fuselagem e da asa de aeronaves. Normalmente, a união dos componentes dessas estruturas é realizada por rebites, já que processos de soldagem com fusão produziriam defeitos indesejáveis. O processo de soldagem por fricção linear com mistura ou Friction Stir Welding (FSW) é uma alternativa à união de chapas de ligas de alumínio por rebites haja vista que não há fusão do material durante a união. No presente trabalho estudou-se o comportamento eletroquímico e a caracterização microestrutural de uma junta sobreposta, composta por um perfil extrudado da liga AA7050-T76511 e uma chapa da liga AA2024-T3, ambos previamente anodizados, soldada por fricção linear com mistura. O comportamento eletroquímico foi avaliado através da utilização da Técnica de Varredura com Eletrodo Vibratório (SVET), medidas do potencial de corrosão e curvas de voltametria cíclica em solução de 0,1 M de NaCl. Correntes anódicas mais intensas foram medidas na região da solda e ainda verificou-se que esta possui menores potenciais de pite e corrosão do que ambas as ligas. Também foi constatada a presença de corrosão intercristalina em ambas as ligas e na região da solda, porém com maior severidade na liga AA2024-T3. / AA2024 and AA7050 aluminum alloys are traditionally used in the manufacture of fuselage structures and aircrafts wings. Usually, the component union of these structures is made using rivets since weld process with melting will produce unwanted defects. The Friction Stir Welding (FSW) process is an alternative way to replace the traditional rivet union of aluminum alloys in the aeronautical and aerospace industries since the material does not melt during the joint. In the present work it has been studied the electrochemical behavior and microstructural characterization of a lap joint composed of an extruded profile of AA7050-T76511 alloy and a sheet of AA2024-T3 alloy, both of them previously anodized and jointed by friction stir welding. The electrochemical behavior was evaluated by means of Scanning Vibrating Electrode Technique (SVET), measurements of the corrosion potential and cyclic voltammetry in 0,1 M NaCl. Higher anodic currents were found in the weld region, moreover this region has the lowest pit and corrosion potential. Intercrystalline corrosion was found in both alloys and in the weld region, with the highest intensity in the AA2024-T3 alloy.

A crescente escassez dos recursos energéticos renováveis, bem como o contínuo aumento dos seus custos tem requerido nas últimas décadas uma redução drástica no consumo de energia utilizada para o transporte de cargas e passageiros. A indústria siderúrgica pode contribuir decisivamente neste contexto, disponibilizando no mercado aços de maior resistência mecânica, os quais podem ser utilizados em estruturas mais esbeltas. Os aços com elevados teores de Mn (15-30%) representam um desenvolvimento muito recente de ligas ferrosas puramente austeníticas, que reúnem resistência mecânica elevada e grande ductilidade. Além disso, trata-se de ligas de baixo custo devido à eliminação dos elevados teores de Ni necessários para a estabilização da austenita e ao reduzido tempo de processamento, que dispensa tratamentos térmicos e processamentos termomecânicos controlados. Por outro lado, a redução de peso estrutural no setor automobilístico requer não somente a pesquisa de novos aços, mas também a utilização de componentes híbridos, resultantes, entre outros, da união dos aços austeníticos alto Mn com aços comerciais estruturais de alta resistência e baixa liga (ARBL). Nesta dissertação, estudou-se, portanto, a soldabilidade pelo processo de fricção e mistura mecânica (SFMM) de aço austenítico alto Mn com efeito TRIP (plasticidade induzida por transformação martensítica) com aço ARBL processado termomecanicamente tipo XABO500 (ThyssenKrupp Steel, limite de escoamento > 460 MPa). As placas de aço TRIP foram fabricadas na EESC-USP com composição Fe-22.5% Mn-0.4% C através de fundição sob atmosfera protetora de argônio, tratamento térmico de homogenização e laminação a quente a 1150°C. As juntas dissimilares TRIP-ARBL foram produzidas com chapas de 3.5 mm de espessura. Os ensaios de soldagem SFMM foram conduzidos com ferramenta de compósito PCBN-WRe. O aporte térmico de soldagem foi variado através do uso de três velocidades de rotação da ferramenta: 300, 400 e 500 rpm, e o avanço foi de 100 mm/min. Dois deslocamentos (offsets) da ferramenta foram investigados: +1.0 e +2.0 mm em direção ao aço TRIP. Os resultados revelaram um acabamento superficial satisfatório das juntas soldadas com 300 e 400 rpm. A penetração de soldagem aumentou com a velocidade de rotação da ferramenta e com um maior deslocamento da ferramenta em direção ao aço TRIP devido ao crescimento do aporte térmico. A SFMM produziu em ambos os lados das juntas dissimilares uma microestrutura caracterizada apenas por zona de mistura (ZM) e zona termicamente afetada (ZTA), não sendo observada a formação de zonas termomecanicamente afetadas (ZTMA). Na ZM do aço ARBL, a SFMM produziu uma microestrutura polifásica, contendo misturas de ferrita acicular, bainita e martensita. O lado TRIP da ZM não exibiu sinais de transformação martensítica induzida por deformação e sofreu recristalização dinâmica com a formação de uma austenita refinada em comparação com o metal de base. A junta produzida com menor aporte térmico (300 RPM e Offset +1) apresentou os maiores picos de dureza na ZM do aço TRIP devido à maior taxa de resfriamento e, consequentemente, a microestrutura mais fina. Apesar dos maiores picos de dureza, a junta produzida com 300 RPM e Offset +1 apresentou o melhor desempenho no ensaio de tração, atingindo o maior percentual de alongamento a fratura e rompendo no metal de base ARBL. Isso se deve provavelmente à formação de ferrita acicular mais fina na ZM do aço ARBL com microestrutura entrelaçada e de maior tenacidade, se comparado com o metal de base ARBL. / The increasing scarcity of renewable energy resources and their continuously rising costs have required in the last decades a drastic reduction in the energy consumption for the transportation of goods and passengers. The steel industry can decisively contribute in this context by providing the market with steel grades of increased mechanical strength, which can be incorporated into light-weight structures. Steels with high Mn contents (15-30%) represent a recent development of austenitic ferrous alloys that combine elevated mechanical strength with high ductility. In addition, those steel grades correspond to low cost alloys due to the replacement of the high Ni contents necessary to stabilize the austenite as well as the reduced manufacturing time that does not involve subsequent heat treatments or controlled thermo-mechanical processing. On the other hand, the reduction of structural weight in the automotive sector does not only require the research on novel steels, but also the use of hybrid components that result among others from joining austenitic high-Mn steels to commercial structural high-strength low-alloyed (HSLA) steel grades. In this work, we studied therefore the friction stir weldability of an austenitic high-Mn steel with TRIP (transformation induced plasticity) effect to the thermomechanically processed HSLA XABO500 steel grade (ThyssenKrupp Steel, yield strength > 460 MPa). High-Mn TRIP steel plates were produced at the EESC-USP with the chemical composition of Fe-22.5% Mn-0.4% C by casting under protective argon atmosphere, followed by homogenization treatment and hot rolling at 1150°C. The dissimilar TRIP-HSLA joints were produced using 3.5 mm thick plates. The friction stir welding (FSW) experiments were carried out with a tool made of a PCBN-WRe composite. The heat input was varied by using three tool rotational speeds: 300, 400 and 500 rpm. The welding speed was set to 100 mm/min. Two different tool offsets were investigated: +1.0 and +2.0 mm towards the high-Mn TRIP steel. The results revealed that a satisfactory surface finishing is achieved for the butt-joints produced with 300 and 400 rpm. The welding penetration increased for higher tool rotational speeds and larger tool offsets towards the TRIP steel because of an increased heat input. FSW produced at both sides of the dissimilar joints a microstructure characterized by only stir zone (SZ) and heat-affected zone (HAZ). Thermo-mechanical affected zones (TMAZ) could not be observed. In the SZ of the HSLA steel, FSW produced a multiphase microstructure that contains a mixture of acicular ferrite, bainite and martensite. The TRIP side of the SZ did not exhibit traces of strain induced martensitic transformation and underwent dynamic recrystallization with the formation of a fine-grained austenite in comparison to the base material. The butt-joint produced with the lowest heat input (300 RPM and Offset +1) developed the highest hardness peaks in the SZ of the TRIP steel because of the increased cooling rate and, consequently, the more refined microstructure. In spite of the hardest zones, the butt-joint produced with 300 RPM and offset +1 achieved the best performance in the tensile tests by reaching the largest elongation to fracture and having the failure in the HSLA base material. This is likely promoted by the formation of a more refined acicular ferrite in the SZ of the HSLA steel with interpenetrated microstructure and enhanced toughness in comparison to the HSLA base material.