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Olsen, Eric. « Friction stir welding of high-strength automotive steel / ». Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1911.pdf.
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Olsen, Eric Michael. « Friction Stir Welding of High-Strength Automotive Steel ». BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/951.
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The following thesis is a study on the ability to create acceptable welds in thin-plate, ultra-high-strength steels (UHSS) by way of friction stir welding (FSW). Steels are welded together to create tailor-welded blanks (TWB) for use in the automotive industry. Dual Phase (DP) 590, 780, and 980 steel as well as Transformation-Induced Plasticity (TRIP) 590 steel with thicknesses ranging from 1.2 mm to 1.8 mm were welded using friction stir welding under a variety of processing conditions, including experiments with dissimilar thicknesses. Samples were tested under tensile loads for initial determination if an acceptable weld had been created. Acceptable welds were created in both TRIP 590 and DP 590 at speeds up to 102 centimeters-per-minute. No acceptable welds were created in the DP 780 and DP 980 materials. A series of microhardness measurements were taken across weld samples to gain understanding as to the causes of failure. These data indicate that softening, caused by both excessive heat and insufficient heat can result in weld failure. Not enough heat causes the high concentration of martensite in these materials to temper while too much heat can cause excessive hardening in the weld, through the formation of even more martensite, which tends to promote failure mode during forming operations. Laser welding is one of the leading methods for creating tailor-welded blank. Therefore, laser welded samples of each material were tested and compared to Friction Stir Welded samples. Lower strength and elongation are measured in weld failure while the failure location itself determines the success of a weld. In short, an acceptable weld is one that breaks outside the weld nugget and Heat Affected Zone (HAZ) and where the tensile strength (both yield and ultimate) along with the elongation are comparable to the base material. In unacceptable welds, the sample broke in the weld nugget or HAZ while strength and elongations were well below those of the base material samples.
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Hartman, Trent J. « Friction Stir Spot Welding of Ultra-High Strength Steel ». BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3302.
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Friction stir spot welding (FSSW) is quickly becoming a method of interest for welding of high strength steel (HSS) and ultra high strength steel (UHSS). FSSW has been shown to produce high quality welds in these materials, without the drawbacks associated with fusion welding. Tool grade for polycrystalline cubic boron nitride (PCBN) tools has a significant impact on wear resistance, weld quality, and tool failure in FSSW of DP 980 steel sheet. More specifically, for a nominal composition of 90% CBN, the grain size has a significant impact on the wear resistance of the tool. A-type tools performed the best, of the three grades that were tested in this work, because the grain size of this grade was the finest, measuring from 3-6 microns. The effect of fine grain size was less adhesion of DP 980 on the tool surface over time, less abrasive wear, and better lap shear fracture loads of the welds that were produced, compared to the other grades. This is explained by less exposure of the binder phase to wear by both adhesion and abrasion during welding of DP 980. A-type tools were the most consistent in both the number of welds per tool, and the number of welds that reached acceptable lap shear fracture loads. B-type tools, with a bimodal grain size distribution (grain size of 4 – 40 microns) did a little bit better than C-type tools (grain size of 12-15 microns) in terms of wear, but neither of them were able to achieve consistent acceptable lap shear fracture load values after the first 200 welds. In fact only one out of five C-type tools was able to produce acceptable lap shear fracture loads after the first 100 welds.
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Sidhar, Harpreet. « Friction Stir Welding of High Strength Precipitation Strengthened Aluminum Alloys ». Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862787/.
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Rising demand for improved fuel economy and structural efficiency are the key factors for use of aluminum alloys for light weighting in aerospace industries. Precipitation strengthened 2XXX and 7XXX aluminum alloys are the key aluminum alloys used extensively in aerospace industry. Welding and joining is the critical step in manufacturing of integrated structures. Joining of precipitation strengthened aluminum alloys using conventional fusion welding techniques is difficult and rather undesirable in as it produces dendritic microstructure and porosities which can undermine the structural integrity of weldments. Friction stir welding, invented in 1991, is a solid state joining technique inherently benefitted to reduces the possibility of common defects associated with fusion based welding techniques.
Weldability of various 2XXX and 7XXX aluminum alloys via friction stir welding was investigated. Microstructural and mechanical property evolution during welding and after post weld heat treatment was studied using experimental techniques such as transmission electron microscopy, differential scanning calorimetry, hardness testing, and tensile testing. Various factors such as peak welding temperature, cooling rate, external cooling methods (thermal management) which affects the strength of the weldment were studied. Post weld heat treatment of AL-Mg-Li alloy produced joint as strong as the parent material. Modified post weld heat treatment in case of welding of Al-Zn-Mg alloy also resulted in near 100% joint efficiency whereas the maximum weld strength achieved in case of welds of Al-Cu-Li alloys was around 80-85% of parent material strength. Low dislocation density and high nucleation barrier for the precipitates was observed to be responsible for relatively low strength recovery in Al-Cu-Li alloys as compared to Al-Mg-Li and Al-Zn-Mg alloys.
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Ratanathavorn, Wallop. « Dissimilar joining of aluminium to ultra-high strength steels by friction stir welding ». Doctoral thesis, KTH, Svetsteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207356.
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Multi-material structures are increasingly used in vehicle bodies to reduce weight of cars. The use of these lightweight structures is driven by requirements to improve fuel economy and reduce CO2 emissions. The automotive industry has replaced conventional steel components by lighter metals such as aluminium alloy. This is done together with cutting weight of structures using more advanced strength steels. However, sound joining is still difficult to achieve due to differences in chemical and thermal properties. This research aims to develop a new innovative welding technique for joining aluminium alloy to ultra-high strength steels. The technique is based on friction stir welding process while the non-consumable tool is made of an ordinary tool steel. Welding was done by penetrating the rotating tool from the aluminium side without penetrating into the steel surface. One grade of Al-Mg aluminium alloy was welded to ultra-high strength steels under lap joint configuration. Different types of steel surface coatings including uncoated, hot-dipped galvanised and electrogalvanised coating have been studied in order to investigate the influence of zinc on the joint properties. The correlation among welding parameters, microstructures, intermetallic formation and mechanical properties are demonstrated in this thesis. Results have shown that friction stir welding can deliver fully strong joints between aluminium alloy and ultra-high strength steels. Two intermetallic phases, Al5Fe2 and Al13Fe4, were formed at the interface of Al to Fe regardless of surface coating conditions. The presence of zinc can improve joint strength especially at low heat input welding due to an increased atomic bonding at Al-Fe interface. The formation of intermetallic phases as well as their characteristics has been demonstrated in this thesis. The proposed welding mechanisms are given based on metallography investigations and related literature.QC 20170519
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Abbasi, Gharacheh Majid. « Microstructural Evaluation in Friction Stir Welded High Strength Low Alloy Steels ». BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/3099.
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Understanding microstructural evolution in Friction Stir Welding (FSW) of steels is essential in order to understand and optimize the process. Ferritic steels undergo an allotropic phase transformation. This makes microstructural evolution study very challenging. An approach based on Electron Backscattered Diffraction (EBSD) and phase transformation orientation relationships is introduced to reconstruct pre-transformed grain structure and texture. Reconstructed pre-transformed and post-transformed grain structures and textures were investigated in order to understand microstructural evolution. Texture results show that there is evidence of shear deformation as well as recrystallization in the reconstructed prior austenite. Room temperature ferrite exhibits well-defined shear deformation texture components. Shear deformation texture in the room temperature microstructure implies that FSW imposes deformation during and after the phase transformation. Prior austenite grain boundary analysis shows that variant selection is governed by interfacial energy. Variants that have near ideal BCC/FCC misorientation relative to their neighboring austenite and near zero misorientation relative to neighboring ferrite are selected. Selection of coinciding variants in transformed prior austenite Σ3 boundaries supports the interfacial-energy-controlled variant selection mechanism.
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Karki, Utsab. « Experimental and Numerical Study of High-Speed Friction Stir Spot Welding of Advanced High-Strength Steel ». BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5521.
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With the desire to lighten the frame while keeping or increasing the strength, Advanced High-Strength Steels (AHSS) have been developed for use in the automotive industry. AHSS meet many vehicle functional requirements because of their excellent strength and acceptable ductility. But joining AHSS is a challenge, because weldability is lower than that of mild steels. Friction stir spot welding (FSSW) is a solid state joining process that can provide a solution to the weldability issues in AHSS, but FSSW has not been studied in great detail for this application. In this work, Si3N4 tools were used for FSSW experiments on DP 980 steel with 1.2mm thickness. Joint strength was measured by lap shear tension testing, while thermocouples were used for the temperature measurements. A finite element model was developed in order to predict material flow and temperatures associated with FSSW. Since a 3D model of the process is very time consuming, a novel 2D model was developed for this study. An updated Lagrangian scheme was employed to predict the flow of sheet material, subjected to the boundary conditions of the fixed backing plate and descending rotating tool. Heat generation by friction was computed by including the rotational velocity component from the tool in the thermal boundary conditions. Material flow was calculated from a velocity field while an isotropic, viscoplastic Norton-Hoff law was used to compute the material flow stress as a function of temperature, strain and strain rate. Shear stress at the tool/sheet interface was computed using the viscoplastic friction law. The model predicted welding temperatures to within 4% of the experiments. The welding loads were significantly over predicted. Comparison with a 3D model of FSSW showed that frictional heating and the proportion of total heat generated by friction were similar. The position of the joint interface was reasonably well predicted compared to experiment.
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Saunders, Nathan David. « High Speed Friction Stir Spot Welding on DP 980 Steel:Joint Properties and Tool Wear ». BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3003.
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With the desire to improve passenger safety and fuel efficiency, Ultra High Strength Steels (UHSS) have been developed for use in the automotive industry. UHSS are high strength steels with high ductility and strength. DP 980 is one of these UHSS being applied in automobile manufacturing. DP 980 is difficult to join with Resistance Spot Welding (RSW) because of the high carbon content and alloying in this material. The weld becomes brittle when it solidifies during the welding process. With the desire and motivation of widely using UHSS, new welding processes are needed to be developed in order to effectively join DP 980. Friction Stir Spot Welding (FSSW) is a developing welding process aimed to replace RSW in the automotive industry because of its ability to join materials at a lower temperature. Currently the welding loads of the tools are higher than 2000 pounds, ranging from 3,000 to 5,000 pounds, which exceeds the limit of the welding robots in the automotive factories. It is proposed that the welding loads can be reduced by increasing the spindle speed of the FSSW tool. Other focuses in the research include increasing the life of the tool and developing acceptable welding parameters for High Speed FSSW. The experimental work done for this thesis provided support that weld strength can be obtained at levels above the acceptable standard for DP 980 material (greater than 2400 pound lap shear fracture load for 1.2 mm material) while keeping the vertical load on the welding machine spindle below 2000 lbs.
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Tungala, Vedavyas. « Exceptional Properties in Friction Stir Processed Beta Titanium Alloys and an Ultra High Strength Steel ». Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984167/.
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The penchant towards development of high performance materials for light weighting engineering systems through various thermomechanical processing routes has been soaring vigorously. Friction stir processing (FSP) - a relatively new thermomechanical processing route had shown an excellent promise towards microstructural modification in many Al and Mg alloy systems. Nevertheless, the expansion of this process to high temperature materials like titanium alloys and steels is restricted by the limited availability of tool materials. Despite it challenges, the current thesis sets a tone for the usage of FSP to tailor the mechanical properties in titanium alloys and steels. FSP was carried out on three near beta titanium alloys, namely Ti6246, Ti185 and Tiβc with increasing β stability index, using various tool rotation rates and at a constant tool traverse speed. Microstructure and mechanical property relationship was studied using experimental techniques such as SEM, TEM, mini tensile testing and synchrotron x-ray diffraction. Two step aging on Ti6246 had resulted in an UTS of 2.2GPa and a specific strength around 500 MPa m3/mg, which is about 40% greater than any commercially available metallic material. Similarly, FSP on an ultra-high strength steel―Eglin steel had resulted in a strength greater than 2GPa with a ductility close to 10% at around 4mm from the top surface of stir zone (SZ). Experimental techniques such as microhardness, mini-tensile testing and SEM were used to correlate the microstructure and properties observed inside SZ and HAZ's of the processed region. A 3D temperature modeling was used to predict the peak temperature and cooling rates during FSP. The exceptional strength ductility combinations inside the SZ is believed to be because of mixed microstructure comprised of various volume fractions of phases such as martensite, bainite and retained austenite.
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Palanivel, Sivanesh. « Thermomechanical Processing, Additive Manufacturing and Alloy Design of High Strength Mg Alloys ». Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849628/.
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The recent emphasis on magnesium alloys can be appreciated by following the research push from several agencies, universities and editorial efforts. With a density equal to two-thirds of Al and one-thirds of steel, Mg provides the best opportunity for lightweighting of metallic components. However, one key bottleneck restricting its insertion into industrial applications is low strength values. In this respect, Mg-Y-Nd alloys have been promising due to their ability to form strengthening precipitates on the prismatic plane. However, if the strength is compared to Al alloys, these alloys are not attractive. The primary reason for low structural performance in Mg is related to low alloying and microstructural efficiency. In this dissertation, these terminologies are discussed in detail. A simple calculation showed that the microstructural efficiency in Mg-4Y-3Nd alloy is 30% of its maximum potential. Guided by the definitions of alloying and microstructural efficiency, the two prime objectives of this thesis were to: (i) to use thermomechanical processing routes to tailor the microstructure and achieve high strength in an Mg-4Y-3Nd alloy, and (ii) optimize the alloy chemistry of the Mg-rare earth alloy and design a novel rare—earth free Mg alloy by Calphad approach to achieve a strength of 500 MPa.
Experimental, theoretical and computational approaches have been used to establish the process-structure-property relationships in an Mg-4Y-3Nd alloy. For example, increase in strength was observed after post aging of the friction stir processed/additive manufactured microstructure. This was attributed to the dissolution of Mg2Y particles which increased the alloying and microstructural efficiency. Further quantification by numerical modeling showed that the effective diffusivity during friction stir processing and friction stir welding is 60 times faster than in the absence of concurrent deformation leading to the dissolution of thermally stable particles. In addition, the investigation on the interaction between dislocations and strengthening precipitate revealed that, specific defects like the I1 fault aid in the accelerated precipitation of the strengthening precipitate in an Mg-4Y-3Nd alloy. Also, the effect of external field (ultrasonic waves) was studied in detail and showed accelerated age hardening response in Mg-4Y-3Nd alloy by a factor of 24.
As the bottleneck of low strength is addressed, the answers to the following questions are discussed in this dissertation: What are the fundamental micro-mechanisms governing second phase evolution in an Mg-4Y-3Nd alloy? What is the mechanical response of different microstructural states obtained by hot rolling, friction stir processing and friction stir additive manufacturing? Is defect engineering critical to achieve high strength Mg alloys? Can application of an external field influence the age hardening response in an Mg-4Y-3Nd alloy? Can a combination of innovative processing for tailoring microstructures and computational alloy design lead to new and effective paths for application of magnesium alloys?
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Wu, Hao. « Systematic analysis of the advantages of stationary shoulder friction stir welding in joining high strength aluminium alloy AA7050-T7651 ». Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/systematic-analysis-of-the-advantages-of-stationary-shoulder-friction-stir-welding-in-joining-high-strength-aluminium-alloy-aa7050t7651(4fe4b645-47c7-4924-90a3-7879bd9bfaf0).html.
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Stationary (static) shoulder friction stir welding (SSFSW) is a variant of conventional friction stir welding (FSW) that was originally invented to improve the quality of welds produced with titanium alloys. Its predominant advantage is a reduction of the severe through thickness temperature gradients seen in conventional FSW, when welding low thermal conductivity alloy. However, SSFSW has rarely been utilised as a method to weld aluminium alloys because it is generally thought that in conventional FSW the rotating shoulder plays an essential role in the heat generation and, due to the high thermal conductivity of aluminium alloys, a rotating shoulder is beneficial for the welding process. In the work presented, the advantages of SSFSW have been examined when welding a typical high strength aluminium alloy AA7050-T7651. The process window for each approach has first been determined, and the optimum welding conditions were systematically evaluated, using power-rotation rate curves. Direct comparison of the two processes was subsequently carried out under these optimum conditions. It has been demonstrated that SSFSW can dramatically improve the quality of a weld's surface finish. Under optimum conditions it has also been shown that SSFSW was able to weld with approximately a 30% lower heat input than FSW and the stationary shoulder led to a narrower heat affected zone (HAZ). As a result, the through thickness properties of SSFSW were much better and more homogeneous than that for FSW, in terms of grain sizes, hardness and cross-weld mechanical properties. Uniaxial tensile tests proved that the average tensile strength of SSFSW samples was around 500 MPa, which was about 100 MPa larger than that of the FSW sample. Also, it was shown that during tensile testing the deformation zones, which correspond to minima in the hardness distribution of SSFSW welds, were about half the size of those found in FSW welds under the same traverse speed. The mechanisms that give rise to these advantages have been investigated systematically, focusing on directly comparing the SSFSW and FSW processes, and are discussed aided by finite element modelling (FEM) of the heat distribution in welds produced by each process and microstructural investigations.
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Wei, Lingyun. « Investigate Correlations of Microstructures, Mechanical Properties and FSW Process Variables in Friction Stir Welded High Strength Low Alloy 65 Steel ». BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2032.
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The present study focuses on developing a relationship between process variables, mechanical properties and post weld microstructure in Friction Stir Welded HSLA 65 steel. Fully consolidated welds can be produced in HSLA 65 steel by PCBN Convex-Scrolled-Shoulder-Step-Spiral (CS4) tool over a wide range of parameters. Microstructures in the nugget center (NC) are dominated by lath bainite and a few polygonal/allotriomorphic grain boundary ferrites. FSW dependent variables are related to FSW independent variables by non-linear relationship. Heat input is identified to be the best parameter index to correlate with microstructures. With increasing heat input, the volume of bainite is reduced, the shape of bainite is more curved and grain/lath size become coarser. A linear relationship was established between heat input and semi-quantitative post-weld microstructures based on the optical microstructures. Further analysis has been applied on the NC to obtain more fundamental understanding of FSW. The new approach via Orientation Imaging Microscopy (OIM) was developed to acquire quantitative microstructural data including bainite lath/packet and prior austenite grain size (PAG). A linear relationship between heat input and quantitative microstructural features in the NC have been established. Mechanical properties exhibits linear relationship with heat input. These correlations can be utilized to determine FSW weld parameter to get desired mechanical properties welds.
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Wood, Shane Forrest. « Manipulation and Automation of FBJ Short-Axis Fasteners ». BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7311.
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Legislative and market pressures are pushing automakers to achieve new fuel economy requirements in the coming years. To help achieve these goals automakers are reducing the overall weight of the vehicle by increasing the use of high-strength aluminum and advanced high-strength steels, and with this increased use comes the desire to quickly, and securely, join these materials within the vehicle. Friction bit joining is a process that lends itself well to joining these materials. This process uses consumable fasteners that need to be used in an automated production line. The geometry of these fasteners causes two main problems: the bits have a short longitudinal axis, which makes them difficult to orient, and the welding platform may be used at different angles; requiring a robust reloading system that is indifferent to its orientation.Our research explored ways that these short axis FBJ fasteners could be handled and transported using various automated methods. We tested the use of small mechanical carriages and magnetic tracks to test their viability for transporting FBJ fasteners. The two different types of fasteners that were used in the project are described. Blow feed tubes ended up being a reliable method of transportation given that the fastener has suitable geometry. The superior bit and feed system design were bench tested using a manually controlled feed system. The system was tested in various orientations to test the robustness of the system since the system was designed to be part of the end effector on a production line robot. The testing revealed that the feed tube is a reliable method of bit transportation and mechanical jaws are a suitable solution for FBJ fastener manipulation. These jaws have several key design features that dramatically increase their effectiveness. Suggestions for future work would be an optimized feed tube cross section, improved material properties in the bit jaw, and more air flow at a higher pressure through the feed tube.
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Mendonça, Roberto Ramon. « Soldagem por fricção e mistura mecânica de aço austenítico alto manganês com efeito TRIP ». Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-14102014-082116/.
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O desenvolvimento e utilização de novos materiais, mais leves e com propriedades mecânicas superiores aos atuais, se mostram extremamente importantes devido à redução de peso e consequentemente redução na emissão de gases poluentes que poderiam gerar. As ligas de Fe-Mn-C com elevados teores de Mn (20-30%) representam um desenvolvimento muito recente de aços austeníticos, que, através dos seus mecanismos diferenciados de deformação reúnem elevada resistência mecânica com grande ductilidade. Essa nova classe de materiais estruturais possibilita uma efetiva redução de custos na produção através do reduzido tempo de processamento (sem a necessidade de tratamentos térmicos especiais e de processamentos termomecânicos controlados). A soldagem é, atualmente, o mais importante processo de união de metais usado no setor industrial. Dentro da variada gama de processos de soldagem existentes, a soldagem por fricção e mistura mecânica (SFMM, em inglês: Friction Stir Welding - FSW) se destaca por ser um processo de união no estado sólido que apresenta uma série de vantagens sobre as tecnologias convencionais de soldagem por fusão. Do ponto de vista metalúrgico, uma das suas principais vantagens se manifesta justamente na junção de materiais dissimilares, visto que o grau de mistura de composições e as transformações de fases entre materiais incompatíveis podem ser minimizados. Outra vantagem é que há um refino de grão no cordão de solda comparado com a microestrutura fundida que se forma nos processos convencionais. Este trabalho teve como objetivo produzir em escala laboratorial os aços de alta liga ao manganês com efeito TRIP, avaliar o impacto da velocidade de rotação da ferramenta na soldagem por fricção e mistura mecânica e avaliar a microestrutura e propriedades mecânicas das juntas soldadas. A microestrutura das juntas soldadas caracterizou-se pela presença apenas da zona de mistura e do metal base, além da formação de \'anéis de cebola\' na zona de mistura, esta não mostrou sinais de transformação martensítica induzida por deformação e sofreu recristalização dinâmica para todas as velocidades de rotação investigadas com a formação de grãos refinados e com morfologia equiaxial. Os corpos de tração fraturaram todos nos metais de base, mostrando que as propriedades mecânicas da zona de mistura foram superiores à do metal base e que a variação de aporte térmico alcançada com a velocidade de rotação da ferramenta não comprometeu a qualidade das juntas soldadas.The development and application of new light materials with superior mechanical properties is extremely important to weight reduction in vehicles and consequently reduction of greenhouse gases emission. The Fe-Mn-C steels with high Mn (20-30%) are a recent development of austenitic steels, which, due to their different mechanisms of deformation, possesses high strength and high ductility as well. In addition, this new type of structural steel allows an effective reduction of manufacturing costs due to its reduced processing time (it does not require special heat treatments and controlled thermo mechanical processing). Welding has been one of the most important processes for joining metals. Among the available welding processes, friction stir welding (FSW) is notable for being a solid state process with great advantages over the conventional welding methods. In the mettalurgical point of view, welding dissimilar materials is a significant advantage of FSW over the other process. The main reason is the reduction of mixture of material and phase transformations between the incompatible materials in the weld. Moreover, grain refinement is another advantage from the process. The present study aimed to produce laboratorial scale high Mn steels with TRIP effect, investigate the impact of tool speed ont the microstructure and mechanical properties of friction stir welded joints. The microstructure of the welded joints exhibited only the stirred zone (SZ) and the base material (BM), besides the presence of ´onion rings´ within the stirred zone. The SZ exhibited no signs of martensite suggesting that dynamic recrystallization have occurred for all the speed tested. Moreover, the grains in the SZ had equiaxial morphology and were significantly refined. The fracture of the tensile specimens occurred in the base material, bringing to light that the welding process was beneficial to the mechanical properties. Furthermore, the variation of heat input achieved with the speed did not compromise the quality of welded joints.
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Ericsson, Mats. « Fatigue Strength of Friction Stir Welded Joints in Aluminium ». Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160.
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Martinez, Nelson Y. « Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys ». Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862775/.
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The Al-Zn-Mg-Cu (7XXX series) alloys are amongst the strongest aluminum available. However, they are considered unweldable with conventional fusion techniques due to the negative effects that arise with conventional welding, including hydrogen porosity, hot cracking, and stress corrosion cracking. For this reason, friction stir welding has emerged as the preferred technique to weld 7XXX series alloys. Aluminum 7449 is one of the highest strength 7XXX series aluminum alloy. This is due to its higher zinc content, which leads to a higher volume fraction of eta' precipitates. It is typically used in a slight overaged condition since it exhibits better corrosion resistance. In this work, the welds of friction stir welded aluminum 7449 were studied extensively. Specific focus was placed in the heat affected zone (HAZ) and nugget. Thermocouples were used in the heat affected zone for three different depths to obtain thermal profiles as well as cooling/heating profiles. Vicker microhardness testing, transmission electron microscope (TEM), and differential scanning calorimeter (DSC) were used to characterize the welds. Two different tempers of the alloy were used, a low overaged temper and a high overaged temper. A thorough comparison of the two different tempers was done. It was found that highly overaged aluminum 7449 tempers show better properties for friction stir welding. A heat gradient along with a high conducting plate (Cu) used at the bottom of the run, resulted in welds with two separate microstructures in the nugget. Due to the microstructure at the bottom of the nugget, higher strength than the base metal is observed. Furthermore, the effects of natural aging and artificial aging were studied to understand re-precipitation. Large improvements in strength are observed after natural aging throughout the welds, including improvements in the HAZ.
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Bennett, Christopher J. « Inertia friction welding of high strength aerospace alloys ». Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576153.
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Inertia friction welding is an important industrial joining technique for the production of axisymmetric components. Two parts, one rotating and the other stationary, are brought together under axial load and rotational kinetic energy stored in a flywheel is transformed into thermal energy and plastic deformation through friction at the interface between the work pieces. The process is quick and repeatable and generates good quality welds with a small heat affected zone (HAZ) One of the main objectives of this research was to produce a modelling tool that can be used to represent the welding of high strength aerospace alloys with particular reference to shaft applications. The commercial software DEFORM-2D was used as it contains a 2.5D modelling capability suitable for this application and can be easily used by industry. The aim of the process modelling tool is to reduce development time and cost by the use of a process modelling tool which would mean fewer development welds are required for new material combinations and geometries. Initial models created were based on the nickel-based superalloy, Inconel 718 and the capability was then extended to the high strength steels, AerMet 100 and S/CMV, which are suitable for aero-engine shaft applications. Material data required to run weld models was defined and a test programme commissioned in order to obtain the properties for the high-strength steels. Microstructural investigations, including continuous cooling and isothermal tests were also carried to determine phase transformation information that was relevant to the welding process. This included the presence of the "bainite nose", and the volume change associated with the martensite transformation on cooling. The latter was shown to have a significant effect on the residual stresses developed in as-welded components. The volume changes are shown to act as a stress relief of up to 1000MPa in the HAZ of the weld. Experimental testing, which included thermal imaging and thermocouple measurements, was carried out in order to gain more insight into the inertia friction welding of the high strength steels. This testing also included some tests using novel welding techniques to attempt to reduce the post-weld cooling rate and the effects of these techniques on the cooling rate are presented. These tests also provided data for validation of the weld model. The research concludes that DEFORM-2D can be used to model the IFW process between high-strength aerospace materials for aero-engine shaft applications and typical results show an error of ±15% with respect to the final upset value.
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Thurlby, Nickolas. « Advances in high rotational speed – friction stir welding for naval applications ». Thesis, Wichita State University, 2009. http://hdl.handle.net/10057/2414.
Texte intégralRésumé :
Changing operational requirements within the Navy defines the need for lighter, faster ships with increased range and payload. To achieve these requirements the Navy is investing in new hull forms and aluminum alloys for the Littoral Combat Ship (LCS), the Landing Helicopter Assault (Replacement) Ship, and the Joint High Speed Vessel. Friction stir welding (FSW) has proven to be a viable means for joining aluminum during the vessel manufacturing process for LCS, and is a likely joining process for other high speed aluminum vessels. While producing welds of high quality, FSW is characterized by high equipment costs and lack of field repair methods. This report outlines a U.S. Navy-Wichita State University research effort to develop high rotational speed – friction stir welding (HRS-FSW), a process that offers the potential for significant reductions in the size, mass, and cost of FSW systems for both assembly and repair (conventional and/or ―in-situ‖) welding.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering
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Mondal, Barnali. « Process-Structure-Property Relationships in Friction Stir Welded Precipitation Strengthened Aluminum Alloys ». Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1505263/.
Texte intégralRésumé :
Through a series of carefully designed experiments, characterization and some modeling tools, this work is aimed at studying the role of thermal profiles on different microstructural zones and associated properties like strength and corrosion through a variation of weld parameters, thermal boundary conditions and material temper. Two different alloys belonging to the Al-Cu and Al-Cu-Li system in different temper conditions- peak aged (T8) and annealed (O) were used. A 3D-thermal pseudo mechanical (TPM) model is developed for the FSW process using heat transfer module in COMSOL Multiphysics and is based on a heat source wherein the temperature dependent yield shear stress is used for the heat generation. The precipitation and coarsening model is based on the Kampmann and Wagner theoretical framework and accounts for the competition between the various nucleation sites for both metastable and equilibrium precipitates. The model predicts different precipitate mean radius and volume fraction for the various zones in the friction stir welded material. A model for the yield strength is developed which considers contributions from different strengthening mechanisms. The predictions of the each models have been verified against experimental data and literature. At constant advance per rotation, the peak temperature decreases with a decrease in traverse speed and increases with an increase in tool rotation. Weld properties were significantly affected by choice of thermal boundary conditions in terms of backing plate diffusivity. Weld conditions with a higher peak temperature and high strain rate results in more dissolution of precipitates and fragmentation of constituent particles resulting in a better corrosion behavior for the weld nugget. For a peak aged temper of 2XXX alloys, the weld nugget experiences dissolution of strengthening precipitates resulting in a lower strength and the Heat affected zone (HAZ) experiences coarsening of precipitates. For an annealed material, both the weld nugget and HAZ experiences dissolution of precipitates with an increase in strength in the weld nugget.
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Wright, Arnold David. « Effective Temperature Control for Industrial Friction Stir Technologies ». BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9134.
Texte intégralRésumé :
Systematic investigation of the Friction Stir Welding (FSW) process shows that a fixed rotational velocity and feed rate may not yield uniform mechanical properties along the length of a weldment. Nevertheless, correlations between process parameters and post-weld material properties have successfully demonstrated that peak temperature and cooling rate drive post-weld properties. There have been many reported methodologies for controlling friction stir welding, with varying degrees of cost to implement and effectiveness. However, comparing data from uncontrolled FSW of AA 6111-T4 sheet with controlled FSW at temperatures ranging from 375 °C to 450 °C demonstrates that a simplified methodology of a single-loop PID controlling with spindle speed may be used to effectively control temperature. This methodology can be simply used with any machine that already has the ability to actively control spindle speed, and has been previously shown to be able to be auto-tuned with a single weld. Additionally, implementation of this method compared to uncontrolled FSW in AA6111 at linear weld speeds of 1-2 meters per minute showed improved mechanical properties and greater consistency in properties along the length of the weld under temperature control. Further results indicate that a minimum spindle rpm may exist above which tensile specimens did not fracture within the weld centerline, regardless of temperature. This work demonstrates that a straight-forward, PID-based implementation of temperature control at high weld rates can produce high quality welds with auto-tuned gains. This method also shows promise in application to other processes in the Friction Stir family, and preliminary results in an application to the Additive Friction Stir Deposition (AFSD) process are also presented.
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Sederstrom, Jack Hunter. « Spot friction welding of ultra high-strength automotive sheet steel / / ». Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1724.pdf.
Texte intégral
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Sederstrom, Jack H. « Spot Friction Welding of Ultra High-Strength Automotive Sheet Steel ». BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/842.
Texte intégralRésumé :
Spot friction welding (SFW) was performed on ultra high strength steel (UHSS) steel sheet commonly used in automobile manufacturing. Alloys studied included DP780, DP780EG, DP980, and DF140T sheet steel of varying thickness from 1.2 mm to 1.4 mm. Welding was accomplished using a PCBN standard tool. Weld strengths were then compared to a proposed AWS standard. Initial hardness readings were taken in cross sectioned samples. Grain structure in a SFW is presented. Resistance spot welds were created in three steels. This study focuses on the strength of SFW joints as compared to traditional resistance spot welding (RSW) in welding like materials to one another. Cycle times of SFW were also evaluated and compared to production rate cycle times of RSW.
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Prymak, David John. « A New Method of Measuring Flow Stress for Improved Modeling of Friction Stir Welding ». BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9081.
Texte intégralRésumé :
Deficiencies in friction stir welding (FSW) numerical modelling are identified. Applicability of flow stress data derived from hot compression, hot torsion, and split Hopkinson bar testing methods is assessed. A new method of measuring flow stresses in the stir zone of a friction stir welding tool is developed. This test utilizes a non-consumable flat-faced cylindrical tool of different geometries that induces a vertical and rotational load on the material of interest. A constant vertical load and rpm value is used for each test yielding the resulting motor torque and temperature generation to define the material response. Experimental samples are cross-sectioned, polished, and etched to reveal the material flow behavior below the tool. A viscosity-based model is used to quantify the shear stress and rim shear rate present in the shear layer below the tool. This test is referred to as the high-pressure shear (HPS) experiment. A parameter window is developed for two alloys of interest, AA6061-T6 and AA2219-T87 and results are reported. The HPS experiments yields flow stress estimates that are pressure and strain rate dependent. Different tool geometries are explored to understand the impact of the "dead zone"at the center axis of the tool. When compared to hot compression and hot torsion the HPS flow stress datasets trend 20-86 % lower across the two materials tested.
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Dickson, Steven B. « An Investigation of Friction Stir Welding Parameter Effects on Post Weld Mechanical Properties in 7075 AA ». BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5672.
Texte intégralRésumé :
The effects of weld temperature, travel speed, and backing plate thermal diffusivity on themechanical properties of a weld have been studied. A face centered cubic experiment of designwas completed in which the response variables were yield strength, minimum hardness in the HAZ, and charpy impact toughness. Three models were created from the data gathered usinga stepwise regression in order to see the effects of each parameter. For the yield strength andminimum hardness it was found that only travel speed and backing plate thermal diffusivities werestatistically significant to the properties. The charpy impact toughness saw that all three parameterswere statistically significant to its value. In all three models the travel speed had the greatest affecton the material properties.
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Rose, Scott Anthony. « The Effect of Cooling Rate of Friction Stir Welded High Strength Low Alloy Steel ». BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4181.
Texte intégralRésumé :
The friction stir welding of steel has produced a hard zone in several different alloys. Despite its detrimental effects on weld toughness, the reasons behind neither its formation nor a method of reducing its size or effects have been explored. Recent advances in process control allow for direct heat input control, which combined with the use of backing plates of different thermal conductivity allows for an expansion of the process window. These control methods also affect the HAZ cooling rate by providing greater range (a 60% increase compared to a fixed backing plate) and control (five welds within 16 °C/s). This increased range produced microstructures consisting of various forms of ferrite at lower cooling rates and bainite at higher cooling rates. The hard zone was determined to be the result of the formation of the bainite at higher cooling rates and was avoided by keeping the cooling rate below 20 °C/s in HSLA-65.
26
Haji, Hasan Abdalla. « An analysis of microstructure and crystallographic texture in friction stir welded high strength low alloy steel ». Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589542.
Texte intégral
27
Scupin, Peer-Jorge [Verfasser], et Norbert [Akademischer Betreuer] Huber. « Semi-stationary shoulder bobbin tool (S3BT) : a new approach in high speed friction stir welding / Peer-Jorge Scupin ; Betreuer : Norbert Huber ». Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2016. http://d-nb.info/1117086445/34.
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28
Scupin, Peer-Jorge Verfasser], et Norbert [Akademischer Betreuer] [Huber. « Semi-stationary shoulder bobbin tool (S3BT) : a new approach in high speed friction stir welding / Peer-Jorge Scupin ; Betreuer : Norbert Huber ». Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2016. http://nbn-resolving.de/urn:nbn:de:gbv:830-88214957.
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29
Awang, Draup Awang Jefri. « Numerical simulation of the structural response of friction stir welded aluminium 2139-T8 alloy subjected to complex loading configurations ». Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/numerical-simulation-of-the-structural-response-of-friction-stir-welded-aluminium-2139t8-alloy-subjected-to-complex-loading-configurations(a840bd28-102d-4c15-be6c-b4e72631e875).html.
Texte intégralRésumé :
Friction stir welding (FSW) and aluminium alloy 2139-T8 are currently being considered for use in future military vehicles. However, stringent regulations on weld integrity under extreme loading conditions limit the adoption of new technologies. Moreover, current finite element (FE) based methods do not give reliable predictions of strain distribution in welds, which makes it difficult to assess the performance of structures. Therefore, an extensive research program was carried out to develop a generalised finite element (FE) based methodology to predict the response of welded structures under complex loading configurations. The methodology enables the complex distribution of mechanical properties arising from welding, which is linked to microstructural variation, to be incorporated into a macro scale structural model. The method is general, and is applicable for any heat treatable aluminium alloy under a range of joining processes. To achieve this, the microstructure of 2139-T8 alloy was characterised at a range of length scales, with particular emphasis on the size and distribution of strengthening Omega precipitates. 2139-T8 was subjected to bead on plate FSW to enable characterisation of the effects of processing on the local microstructure. In addition, kinetic data for 2139-T8 was generated, allowing a simple softening model to be developed; this allowed the post-weld strength distribution to be predicted. The model was also used to recreate bulk specimens of 2139-T8 with equivalent local weld microstructure, which was verified by transmission electron microscopy. Material with equivalent microstructure was used to estimate the local mechanical property distributions across the weld, including the initial yield stress and plastic response; the mechanical properties of 2139-T8 are known to be representative of 2139-T84. From observations of this combined data, a methodology was developed to enable the estimation of the complex mechanical property distributions arising during welding. Furthermore, an automated computer program was written to implement the property distributions into FE based models. The methodology was verified using data generated for 2139-T8 and was used to simulate the response of FSW 2139-T8 loaded in uniaxial tension. The simulations were verified experimentally using digital image correlation (DIC) and the methodology was shown to demonstrate increased accuracy and reliability over existing FE methods, with respect to strain predictions. In addition, the method eliminates the need to calibrate the structural model to a particular loading configuration. Theoretically, the models are insensitive to loading and this property was tested by extending the model to simulate the strain distribution of large scale welded panels subject to explosive blast loading. The simulations were verified against blast tests where FSW 2139-T84 panels were subjected to blast loading from the detonation of plastic explosive. The results indicate that the modelling methodology developed is capable of producing accurate and reliable predictions of strain distribution in welded structures under complex loading configurations.
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Wei, Lingyun 1972. « Investigating correlations of microstructures, mechanical properties and FSW process variables in friction stir welded high strength low alloy 65 steel / ». Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3195.pdf.
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31
Squires, Lile P. « Friction Bit Joining of Dissimilar Combinations of Advanced High-Strength Steel and Aluminum Alloys ». BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4104.
Texte intégralRésumé :
Friction bit joining (FBJ) is a new method that enables lightweight metal to be joined to advanced high-strength steels. Weight reduction through the use of advanced high-strength materials is necessary in the automotive industry, as well as other markets, where weight savings are increasingly emphasized in pursuit of fuel efficiency. The purpose of this research is twofold: (1) to understand the influence that process parameters such as bit design, material type and machine commands have on the consistency and strength of friction bit joints in dissimilar metal alloys; and (2) to pioneer machine and bit configurations that would aid commercial, automated application of the system. Rotary broaching was established as an effective bit production method, pointing towards cold heading and other forming methods in commercial production. Bit hardness equal to the base material was found to be highly critical for strong welds. Bit geometry was found to contribute significantly as well, with weld strength increasing with larger bit shaft diameter. Solid bit heads are also desirable from both a metallurgical and industry standpoint. Cutting features are necessary for flat welds and allow multiple material types to be joined to advanced high-strength steel. Parameters for driving the bit were established and relationships identified. Greater surface area of contact between the bit and the driver was shown to aid in weld consistency. Microstructure changes resulting from the weld process were characterized and showed a transition zone between the bit head and the bit shaft where bit hardness was significantly increased. This zone is frequently the location of fracture modes. Fatigue testing showed the ability of FBJ to resist constant stress cycles, with the joined aluminum failing prior to the FBJ fusion bond in all cases. Corrosion testing established the use of adhesive to be an effective method for reducing galvanic corrosion and also for protecting the weld from oxidation reactions.
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Weickum, Britney. « Friction Bit Joining of 5754 Aluminum to DP980 Ultra-High Strength Steel : A Feasibility Study ». BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2789.
Texte intégralRésumé :
In this study, the dissimilar metals 5754 aluminum and DP980 ultra-high strength steel were joined using the friction bit joining (FBJ) process. The friction bits were made using one of three steels: 4140, 4340, or H13. Experiments were performed in lap shear, T-peel, and cross tension configurations, with the 0.070" thick 5754 aluminum alloy as the top layer through which the friction bit cut, and the 0.065" thick DP980 as the bottom layer to which the friction bit welded. All experiments were performed using a computer controlled welding machine that was purpose-built and provided by MegaStir Technologies. Through a series of designed experiments (DOE), weld processing parameters were varied and controlled to determine which parameters had a significant effect on weld strength at a 95% confidence level. The parameters that were varied included spindle rotational speeds, Z-command depths, Z-velocity plunge rates, dwell times, and friction bit geometry. Maximum lap shear weld strengths were calculated to be 1425.4lbf and were to be obtained using a bit tip length at 0.175", tip diameter at 0.245", neck diameter at 0.198", cutting and welding z-velocities at 2.6"/min, cutting and welding RPMs at 550 and 2160 respectively, cutting and welding z-commands at -0.07" and -0.12" respectively, cooling dwell at 500 ms, and welding dwell at 1133.8 ms. These parameters were further refined to reduce the weld creation time to 1.66 seconds. These parameters also worked well in conjunction with an adhesive to form weld bonded samples. The uncured adhesive had no effect on the lap shear strengths of the samples. Using the parameters described above, it was discovered that cross tension and T-peel samples suffered from shearing within the bit that caused the samples to break underneath the flange of the bit during testing. Visual inspection of sectioned welds indicated the presence of cracking and void zones within the bit.
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Clark, Tad Dee. « An Analysis of Microstructure and Corrosion Resistance in Underwater Friction Stir Welded 304L Stainless Steel ». Diss., BYU ScholarsArchive, 2005. http://contentdm.lib.byu.edu/ETD/image/etd872.pdf.
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34
Atwood, Lorne Steele. « Friction Bit Joining of Dissimilar Combinations of GADP 1180 Steel and AA 7085 – T76 Aluminum ». BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6400.
Texte intégralRésumé :
Friction Bit Joining (FBJ) is a method used to join lightweight metals to advanced high-strength steels (AHSS). The automotive industry is experiencing pressure to improve fuel efficiency in their vehicles. The use of AHSS and aluminum will reduce vehicle weight which will assist in reducing fuel consumption. Previous research achieved joint strengths well above that which was required in three out of the four standard joint strength tests using DP980 AHSS and 7075 aluminum. The joints were mechanically tested and passed the lap-shear tension, cross-tension, and fatigue cycling tests. The t-peel test configuration never passed the minimum requirements. The purpose of continuing research was to increase the joint strength using FBJ to join the aluminum and AHSS the automotive industry desires to use specifically in the t-peel test. In this study FBJ was used to join 7085 aluminum and GADP1180 AHSS. The galvanic coating on the AHSS and its increased strength with the different aluminum alloy required that all the tests be re-evaluated and proven to pass the standard tests. FBJ is a two-step process that uses a consumable bit. In the first step the welding machine spins the bit to cut through the aluminum, and the second step applies pressure to the bit as it comes in contact with the AHSS to create a friction weld.
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Lu, Jian. « Microstructure Evolution in 304L Stainless Steel Subjected to Hot Torsion at Elevated Temperature ». BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2854.
Texte intégralRésumé :
The current study focus on investigating a relationship between processing variables and microstructure evolution mechanism in 304L stainless steel subjected to hot torsion. The Gleeble 3800 with Mobile Torsion Unit (MTU) is utilized in the current study to conduct hot torsion test of 304L stainless steel. Samples are rotated at 1100℃ in the shear strain rate range of 0.02s-1 to 4.70s-1 and the shear strain range of 0.5 to 4. Orientation imaging microscopy (OIM) technique is used to collect and analyze the microstructure. At low strains (≤1) and strain rate (0.02s-1), average grain size remains relatively constant, but the lengths of DSs and LABs increase within grains. These are characteristics of the dynamic recovery (DRV). With increasing strain and strain rate, the lengths of DSs, LABs and HABs increase, accompanied by the decrease of average grain size. Subgrains with HAB segments are observed. These are characteristics of continuous dynamic recrystallization (CDRX). At strain rates greater than or equal to 0.94s-1, the fraction of deformation texture is about 3 times higher than that of rotated cube texture. The average grain size increases relative to that at a strain rate of 0.20s-1, accompanied by the increase of twin length per area. This indicates that grain growth take place after CDRX. Sigma phase is not observed in the current study due to the lack of static recrystallization (SRX) and the higher cooling rate.
36
Lin, Chien-Hung, et 林建宏. « Study of Friction Stir Spot Welding of High Strength Automotive AZ80-F Magnesium alloy ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/58296672896324093357.
Texte intégralRésumé :
碩士國立屏東科技大學
車輛工程系所
98
Lightweighting has become a key issue in automotive industries recently. Magnesium alloy, consequently, has become one of the major materials for structures. In addition, the solid-state bonding and other excellent features of the friction stir spot welding (FSSW) makes it inherently attractive for body assembly and other similar applications. This study aims to investigate the welding characteristics of the AZ80-F magnesium alloy of FSSW. A 3D finite element coupling model is employed to investigate the effects of welding parameters on the thermal-mechanical behavior of the welds. Then, the experimental samples are made by using FSSW process and, the tensile-shear test, direct tensile test, nano-indentation test and metallographic test are performed to understand the corresponding characteristics of the spot welds. The results show that the welding parameters of tool rotation speed and pressure are more sensitive to the temperature distribution of the welds. In addition, the temperature distribution curve can be used to evaluate the properties of the welds. The results obtained from microstructure observation reveal that the geometry of the tool has a strong effect on the plastic flow and grain size in the welds during the welding process. The welds with the dual-conical tool have the best microstructure distribution and welding strength. Its welding strength increases with the increase of tool rotation speed and pressure to a critical value.
37
Khan, Mohammad Ibraheem. « Spot Welding of Advanced High Strength Steels (AHSS) ». Thesis, 2007. http://hdl.handle.net/10012/2777.
Texte intégralRésumé :
Efforts to reduce vehicle weight and improve crash performance have resulted in increased application of advanced high strength steels (AHSS) and a recent focus on the weldability of these alloys. Resistance spot welding (RSW) is the primary sheet metal welding process in the manufacture of automotive assemblies. Integration of AHSS into the automotive architecture has brought renewed challenges for achieving acceptable welds. The varying alloying content and processing techniques has further complicated this initiative. The current study examines resistance spot welding of high strength and advance high strength steels including high strength low alloy (HSLA), dual phase (DP) and a ferritic-bainitic steel (590R). The mechanical properties and microstructure of these RSW welded steel alloys are detailed. Furthermore a relationship between chemistries and hardness is produced.
The effect of strain rate on the joint strength and failure mode is also an important consideration in the design of welded structures. Current literature, however, does not explain the effects of weld microstructure and there are no comprehensive comparisons of steels. This work details the relationship between the joint microstructure and impact performance of spot welded AHSS. Quasi-static and impact tests were conducted using a universal tensile tester and an instrumented drop tower, respectively. Results for elongation, failure load and energy absorption for each material are presented. Failure modes are detailed by observing weld fracture surfaces. In addition, cross-sections of partially fractured weldments were examined to detail fracture paths during static loading. Correlations between the fracture path and mechanical properties are developed using observed microstructures in the fusion zone and heat-affected-zone.
Friction stir spot welding (FSSW) has proven to be a potential candidate for spot welding AHSS. A comparative study of RSW and FSSW on spot welding AHSS has also been completed. The objective of this work is to compare the microstructure and mechanical properties of Zn-coated DP600 AHSS (1.2mm thick) spot welds conducted using both processes. This was accomplished by examining the metallurgical cross-sections and local hardnesses of various spot weld regions. High speed data acquisition was also used to monitor process parameters and attain energy outputs for each process.
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Bloodworth, Thomas. « On the immersed friction stir welding of AA6061-T6 a metallurgic and mechanical comparison to friction stir welding / ». Diss., 2009. http://etd.library.vanderbilt.edu/available/etd-03302009-100850/.
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Lo, Chu-Chun, et 羅竹君. « Fabrication of High Strength Al-Cu-Ti Alloys by Friction Stir Processing ». Thesis, 2005. http://ndltd.ncl.edu.tw/handle/45704431130317063783.
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Hsieh, Cheng-Yao, et 謝丞堯. « A Study on the Welding Strength and Failure Behaviors of Friction Stir Spot Welded Mg-Al/Mg-Li Dissimilar Magnesium Alloys ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/sh843c.
Texte intégralRésumé :
碩士國立虎尾科技大學
材料科學與工程系材料科學與綠色能源工程碩士班
104
Friction stir spot welding (FSSW) is a kind of solid state welding method developed on the basis of the friction stir welding (FSW) process. The working temperature of FSSW is generally lower than melting temperature of metals, and this process is quite suitable for joining magnesium (Mg) and aluminum (Al) alloys. Light-weight Mg alloys have some advantages, such as high specific strength,high specific stiffness, well recyclability and radiation absorption of electromagnetic waves. The aim of present study is to investigate the microstructure variation, phase composition, microhardness, welding strength and fracture morphologies of FSSW butt-joined AZ91/LZ91 and AZ61/LZ91 dissimilar Mg alloys. Experimental results show that grain size and Mg17Al12 precipitate particles are significantly refined within the welding zone (WZ) due to the intense plastic flow after FSSW joining process. The microhardness with WZ region is obviously higher than the base metals. The increasing microhardness is resulted from the grain refining effect during the FSSW joining process. Tensile testing results show that the average welding strength of A9-L9 joints is about 63.7 MPa. However, the average welding strength of A6-L9 joints is generaly higher than 100 MPa. SEM observations for fracture morphologies show that the fracture of dissimilar joints is occurred from the butt-joining interface. Through the statistical analysis of the Weibull distribution function, FSSW-joined A9-L9 and A6-L9 dissimilar Mg alloys with a wear-out failure model are recognized as reliable joints for further engineering application.
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Su, Fang-Hua, et 蘇芳嬅. « Studies on the Friction Stir Welding of Aluminum Alloy Sheetsby Using High Speed Steel Tool Inserted Aluminum Alloy ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/50225063693950572725.
Texte intégralRésumé :
碩士國立中山大學
機械與機電工程學系研究所
99
In this study, a novel inserted type of friction welding tool was proposed, where the circular rod was embedded in its central axis using the material same as the workpiece, so that it could effectively promote the friction heat quickly and enhance the welding quality. The welding tool was made of the high-speed steel, the workpiece with its embedded material 6061-T6 aluminum alloy. A vertical milling machine equipped with dynamometer, which could measure the power during the friction stir welding, was employed as the experimental apparatus. During the welding process, the K-type thermocouple was used simultaneously in measuring the welding temperature at the interface of joint. The operating conditions of welding were as followings: the welding speed of 800 rpm, the tool inclination of 1° and the clamping force 2kN, the tool with 12mm in diameter and 0.21mm in depth under the downward force about 2 kN. The experiment was conducted into two stages. The first stage was a spot welding to investigate the effect of the ratio of the diameter of embedded material (d) to the diameter of welding tool (D) on the temperature of the interface of joint, the thickness of plastic flow, and the failure load of weld. Experimental results revealed that the interface temperature, the plastic flow thickness, and the failure load of weld are directly proportional to d/D. In comparison with the welding tool without insert (d/D = 0), the maximum interface temperature increased about 1.12 times at d/D = 0.83, the plastic flow thickness increased about 1.52 times, and the failure load of weld increased about 1.45 times. In the second stage, the feeding process was included to investigate the influence of the diameter and the thickness of embedded material on the interface temperature, the plastic flow thickness, and the failure load of weld. Experimental results revealed that the plastic flow thickness was less than 2 mm when the thickness of embedded material was less than 3 mm. However, when the thickness of embedded material was larger than 5 mm, the plastic flow thickness could achieve to 3 mm. Hence, the thickness of embedded material should be larger than 5mm. Moreover, the effect of the diameter of embedded material on the interface temperature and the plastic flow thickness using the feeding process was almost the same as the spot welding. However, in comparison with the welding tool without insert, the failure load of weld increased about two times.
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Jesus, Joel Alexandre da Silva de. « Processamento por Fricção Linear : uma técnica de melhoria da resistência à fadiga de juntas soldadas ». Doctoral thesis, 2019. http://hdl.handle.net/10316/87575.
Texte intégralRésumé :
Tese de Doutoramento em Engenharia Mecânica, na especialidade de Integridade Estrutural, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de CoimbraElementos ou estruturas soldadas são muito comuns em equipamentos mecânicos, sendo estes bastante suscetíveis a falhas por fadiga dado a presença do acidente geométrico (cordão de soldadura) e de defeitos de soldadura muito comuns sobre tudo em soldaduras de ligas de alumínio que por sua vez são bastante utilizadas na industria em geral, pelo que se torna um objeto de estudo importante encontrar formas e técnicas alternativas das tradicionais (refusão, shootpeening, laserpeening, entre outras) para melhorar a performance à fadiga de juntas soldadas nas ligas de alumínio. Sendo a técnica do processamento for fricção linear (PFL) uma tecnologia recente que já demostrou ser excelente para eliminar defeitos e promover modificações macro e microestruturais em matérias não soldados, foi então pensada a sua adaptação para este trabalho e ser aplicada em duas juntas diferentes (topo a topo e em T) soldadas por MIG/GMAW (processo tradicionalmente utilizado para soldar por fusão ligas de alumínio, em atmosfera de gás inerte) e em duas ligas de alumínio distintas (6082-T651 e 5083-H111). Assim, numa primeira fase, o objetivo principal passou pela análise da influência no comportamento mecânico à fadiga em juntas de liga de alumínio soldadas por MIG/GMAW pós-processadas pelo processamento por fricção linear. Passando este estudo não só pela realização de ensaios de fadiga e a sua análise, mas também por realizar análises complementares como análises metalográficas e morfológicas, análises de durezas, análises de resultados de ensaios estáticos (ensaios de tração), análises fractográficas e medição de tensões residuais. Tanto para as juntas topo a topo como em T soldadas por MIG/GMAW e posteriormente processadas utilizando o PFL registrou-se um incremento da resistência á fadiga de entre 30% a 55% para uma vida de 1000000 ciclos dependendo da razão de tensões (R=0 e R=-1), da junta e da liga de alumínio estudada o que compete perfeitamente com outras técnicas mais complexas como shotpeening, laserpeening, refusão, entre outros. A aplicação do PFL provocou a alteração geométrica que diminuiu a concentração de tensões, a introdução de uma camada fina de material refinado e a eliminação de defeitos deixados pela soldadura MIG/GMAW no pé do cordão de soldadura (zona crítica) o que permitiu aumentar o período de iniciação e de nucleação de fendas por fadiga, sendo o incremento mais influenciado pela introdução de uma camada fina de material refinado e a eliminação de defeitos da soldadura MIG/GMAW. Numa segunda fase surgiu a questão de perceber se seria mais vantajoso utilizar o processo MIG/GMAW para soldar as juntas T e posteriormente processar as zonas críticas das soldaduras conseguidas ou aplicar diretamente a soldadura por fricção linear em juntas T. Assim conseguir um termo comparativo, mas também dar um contributo para o desenvolvimento de soldaduras em T por SFL dado a dificuldade em realizar estas soldadura com raios de concordância bem definidos evitando diminuição de espessura e defeitos. Esta parte também passou por análises semelhantes à da primeira fase. Foram conseguidas soldaduras de junta T utilizando a SFL com raios bem definidos, sem defeitos e sem diminuição de espessura em ambas as ligas de alumínio que revelaram um comportamento à fadiga melhor do que as juntas T soldadas por MIG/GMAW, assim como as juntas T soldadas por SFL que apresentaram defeitos do tipo linha de óxidos tiveram uma performance à fadiga mais baixa. O comportamento à fadiga das soldaduras T soldadas por SFL mostraram estar ligeiramente a cima da performance à fadiga das juntas T soldadas por MIG/GMAW pelo que seria mais económico e simples aplicar a SFL diretamente nas juntas T do que soldas as juntas T por MIG/GMAW e posteriormente processá-las com o PFL.
Welded elements or structures are very common in mechanical equipment, and these are quite susceptible to failures due to fatigue due to the presence of the geometric accident (weld bead) and welding defects very common, especially in aluminium alloy welds which are widely used in industry in general, so it becomes an important subject of study to find alternative forms and techniques of traditional ones (reflow, shootpeening, laserpeening, among others) to improve fatigue performance of welded joints in aluminium alloys. Since the technique of friction stir processing (FSP) is a recent technology that has already proved to be excellent for eliminating defects and promoting macro and microstructural modifications in non-welded materials, its adaptation to this work was then thought to be applied in two different joints (but and T joints) welded by MIG / GMAW (traditionally used for welding by fusion aluminium alloys, in inert gas atmosphere) and two different aluminium alloys (6082-T651 and 5083-H111). Thus, in the first phase, the main objective was to analyse the influence on mechanical fatigue behaviour in post-processed MIG/GMAW welded aluminium alloy joints by friction stir processing. This study was carried out not only by performing fatigue tests and their analysis, but also by performing complementary analyses such as metallographic and morphological analysis, hardness analysis, static test results (tensile tests), fractography analysis and stress measurements residual. For butt and T joints welded by MIG/GMAW and further processed using FSP, was recorded an increase in fatigue strength between 30% to 55% for a life of 1000000 cycles depending on the ratio of stresses (R = 0 and R = -1), joint and aluminium alloy studied, which competes perfectly with other more complex techniques such as shotpeening, laserpeening, refining, among others. The application of the PFL caused the geometric alteration that reduced the concentration of stresses, the introduction of a thin layer of refined material and the elimination of defects left by the MIG/GMAW welding process at the weld toe of the weld bead (critical zone). That led to an increase of crack initiation and nucleation period, being the increment most influenced by the introduction of a thin layer of refined material and the elimination of MIG / GMAW weld defects. In a second phase, the question arose as to whether it would be more advantageous to use the MIG/GMAW process in T welds joints and then process the critical zones of the welds achieved or directly apply the friction stir welding (FSW) to T joints. Thus to achieve a comparative term, but also contribute to the development of FSW given the difficulty in realizing these welding with weld toe radius well defined avoiding thickness reduction and welding defects. This part also underwent analyzes similar to the first phase. T-joint welds with weld toes radius well defined, without welding defects and avoiding thickness reduction were achieved using FSW in both aluminium alloys. These welds showed better fatigue behaviour than T-joints welded by MIG/GMAW as well as T-joints welded by SFL that show oxides line defect had a lower fatigue performance. The fatigue behaviour of welds T welded by SFL showed to be slightly above the fatigue performance of T-joints welded by MIG/GMAW, so it would be more economical and simple to apply the SFL directly to the T joints than to weld T joints by MIG/GMAW and then process them with the PFL.