In the friction stir welding (FSW) process, a high-speed rotating tool, which consists of the probe and the shoulder, are employed to plunge into the faying surfaces. By using the friction heating and the stirring action of the material, the solid-state welding is accomplished to joint two pieces of metal by material diffusion to form a densification structure in the weld. According to the experimental results, the mechanism of friction stir welding is as follows: the probe plunge into the sample and the shoulder is in contact with the sample to generate a large amount of friction heat, which causes the materials soft. When the probe moves forward, the soft materials in front of the probe are scratched. The scratched materials are subjected to the rotational and squeeze actions of the shoulder so that they are refilled into the welded surface behind the probe. For the dissimilar metals joint (6061-T6 aluminum and C1100 copper plates), results show that when C1100 copper is located at the advancing side, the measured feed force appears drastic changes and it is also seen that the components of the force for the friction-stir welding of dissimilar metals become more unstable than those for the same metals joint, so that the structure which has been observed by optical microscopy appears to be open with pores and defects so that the welded quality becomes poor. According to the three components of the measured force during FSW process, the friction between the probe and the work piece can be computed. By using the friction theory, the hardness and the yield strength of the materials in front of the probe can be calculated, and then the faying surface temperature is approximately predicted to be 565.5 oC.

Metalle werden oft während ihrer Anwendung korrosiven Bedingungen ausgesetzt, was ihre Alterungsbeständigkeit reduziert. Deswegen werden korrosionsanfällige Metalle, wie Aluminiumlegierungen mit Schutzbeschichtungen versehen, um den Korrosionsprozess aktiv oder passiv zu verhindern. Die klassischen Schutzbeschichtungen funktionieren als physikalische Barriere zwischen Metall und korrosiver Umgebung und bieten einen passiven Korrosionsschutz nur, wenn sie unbeschädigt sind. Im Gegensatz dazu kann die Korrosion auch im Fall einer Beschädigung mittels aktiver Schutzbeschichtungen gehemmt werden. Chromathaltige Beschichtungen bieten heutzutage den besten aktiven Korrosionsschutz für Aluminiumlegierungen. Aufgrund ihrer Giftigkeit wurden diese weltweit verboten und müssen durch neue umweltfreundliche Schutzbeschichtungen ersetzt werden. Ein potentieller Ersatz sind Schutzbeschichtungen mit integrierten Nano- und Mikrobehältern, die mit ungiftigem Inhibitor gefüllt sind. In dieser Arbeit werden die Entwicklung und Optimierung solcher aktiver Schutzbeschichtungen für die industriell wichtige Aluminiumlegierung AA2024-T3 dargestellt Mesoporöse Silika-Behälter wurden mit dem ungiftigen Inhibitor (2-Mercaptobenzothiazol) beladen und dann in die Matrix anorganischer (SiOx/ZrOx) oder organischer (wasserbasiert) Schichten dispergiert. Zwei Sorten von Silika-Behältern mit unterschiedlichen Größen (d ≈ 80 and 700 nm) wurden verwendet. Diese haben eine große spezifische Oberfläche (≈ 1000 m² g-1), eine enge Porengrößenverteilung mit mittlerer Porenweite ≈ 3 nm und ein großes Porenvolumen (≈ 1 mL g-1). Dank dieser Eigenschaften können große Inhibitormengen im Behälterinneren adsorbiert und gehalten werden. Die Inhibitormoleküle werden bei korrosionsbedingter Erhöhung des pH-Wertes gelöst und freigegeben. Die Konzentration, Position und Größe der integrierten Behälter wurden variiert um die besten Bedingungen für einen optimalen Korrosionsschutz zu bestimmen. Es wurde festgestellt, dass eine gute Korrosionsschutzleistung durch einen Kompromiss zwischen ausreichender Inhibitormenge und guten Barriereeigenschaften hervorgerufen wird. Diese Studie erweitert das Wissen über die wichtigsten Faktoren, die den Korrosionsschutz beeinflussen. Somit wurde die Entwicklung effizienter, aktiver Schutzbeschichtungen ermöglicht, die auf mit Inhibitor beladenen Behältern basieren. / Metals are often used in environments that are conducive to corrosion, which leads to a reduction in their mechanical properties and durability. Coatings are applied to corrosion-prone metals such as aluminum alloys to inhibit the destructive surface process of corrosion in a passive or active way. Standard anticorrosive coatings function as a physical barrier between the material and the corrosive environment and provide passive protection only when intact. In contrast, active protection prevents or slows down corrosion even when the main barrier is damaged. The most effective industrially used active corrosion inhibition for aluminum alloys is provided by chromate conversion coatings. However, their toxicity and worldwide restriction provoke an urgent need for finding environmentally friendly corrosion preventing systems. A promising approach to replace the toxic chromate coatings is to embed particles containing nontoxic inhibitor in a passive coating matrix. This work presents the development and optimization of effective anticorrosive coatings for the industrially important aluminum alloy, AA2024-T3 using this approach. The protective coatings were prepared by dispersing mesoporous silica containers, loaded with the nontoxic corrosion inhibitor 2-mercaptobenzothiazole, in a passive sol-gel (SiOx/ZrOx) or organic water-based layer. Two types of porous silica containers with different sizes (d ≈ 80 and 700 nm, respectively) were investigated. The studied robust containers exhibit high surface area (≈ 1000 m² g-1), narrow pore size distribution (dpore ≈ 3 nm) and large pore volume (≈ 1 mL g-1) as determined by N2 sorption measurements. These properties favored the subsequent adsorption and storage of a relatively large amount of inhibitor as well as its release in response to pH changes induced by the corrosion process. The concentration, position and size of the embedded containers were varied to ascertain the optimum conditions for overall anticorrosion performance. Attaining high anticorrosion efficiency was found to require a compromise between delivering an optimal amount of corrosion inhibitor and preserving the coating barrier properties. This study broadens the knowledge about the main factors influencing the coating anticorrosion efficiency and assists the development of optimum active anticorrosive coatings doped with inhibitor loaded containers.

An experimental and numerical study of the isothermal and non-isothermal warm formability of an AA3003 aluminum alloy brazing sheet is presented. Forming limit diagrams were determined using warm limiting dome height (LDH) experiments with in situ strain measurement based on digital image correlation (DIC) techniques. Forming limit curves (FLCs) were developed at several temperature levels (room temperature, 100ºC, 200ºC, 250ºC, and 300ºC) and strain-rates (0.003, 0.018, and 0.1s-1). The formability experiments demonstrated that temperature has a significant effect on formability, whereas forming speed has a mild effect within the studied range. Elevating the temperature to 250C improved the formability more than 200% compared to room temperature forming, while forming at lower speeds increased the limiting strains by 10% and 17% at room temperature and 250ºC, respectively. Non-isothermal deep draw experiments were developed considering an automotive heat exchanger plate. A parametric study of the effects of die temperature, punch speed, and blank holder force on the formability of the part was conducted. The introduction of non-isothermal conditions in which the punch is cooled and the flange region is heated to 250C resulted in a 61% increase in draw depth relative to room temperature forming. In order to develop effective numerical models of warm forming processes, a constitutive model is proposed for aluminum alloy sheet to account for temperature and strain rate dependency, as well as plastic anisotropy. The model combines the Barlat YLD2000 yield criterion (Barlat et al., 2003) to capture sheet anisotropy and the Bergstrom (1982) hardening rule to account for temperature and strain rate dependency. Stress-strain curves for AA3003 aluminum alloy brazing sheet tested at elevated temperatures and a range of strain rates were used to fit the Bergstrom parameters, while measured R-values were used to fit the yield function parameters. The combined constitutive model was implemented within a user defined material subroutine that was linked to the LS-DYNA finite element code. Finite element models were developed based on the proposed material model and the results were compared with experimental data. Isothermal uniaxial tensile tests were simulated and the predicted responses were compared with measured data. The tensile test simulations accurately predicted material behaviour. The user material subroutine and forming limit criteria were then applied to simulate the isothermal warm LDH tests, as well as isothermal and non-isothermal warm deep drawing experiments. Two deep draw geometries were considered, the heat exchanger plate experiments developed as part of this research and the 100 mm cylindrical cup draw experiments performed by McKinley et al. (2010). The strain distributions, punch forces and failure location predicted for all three forming operations were in good agreement with the experimental results. Using the warm forming limit curves, the models were able to accurately predict the punch depths to failure as well as the location of failure initiation for both the isothermal and non-isothermal deep draw operations.

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¢X 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.

7039 aluminum alloys are widely being used in the aerospace, automotive and defense industries in which welding technique is used for their joining. The main problem encountered during the welding of 7039 aluminum alloy is hot cracking. The aim of this study is to understand the effect of welding parameters on the hot cracking behavior of 7039 aluminum alloy by using Modified Varestraint Test (MVT) with Gas Tunsgten Arc Welding (GTAW) technique. During tests, welding speed was selected as varying parameter, welding current was kept constant and to understand the effect of filler materials 5183 and 5356 aluminum alloy filler materials were used. It has been observed that with the change in welding speed hot cracking susceptibility of 7039 aluminum alloy changes. The effect of filler materials is found to be favorable by decreasing the hot cracking susceptibility of 7039 aluminum alloy. Filler material additions also improved the hardness of the weld metal. Based on the cracking mechanism hot cracks were investigated as solidification cracks and liquation cracks. It has been experienced that liquation cracking susceptibility of the filler material added samples has been affected from the magnesium and manganese contents of the weld seams. Effect of solidification range on liquation cracking was also justified with differential thermal analyses. With the micro examinations the intergranular structure of hot cracking is revealed. In addition, the characterization and growth properties of the hot cracks under cyclic load were tried to be understood and the fractography of these cracks were taken.

Hydraulic bulge forming has been used as a method to determine the properties of sheet metal alloys in biaxial stretching at room temperature. Gas-pressure bulge forming alleviates the issues of using hydraulic fluids when the tests are conducted at high temperatures (above 200°C). Testing a sheet metal alloy by gas-pressure blow-forming (GPBF) under controlled temperature and pressure conditions requires an accurate and reliable mechanism that delivers repeatable results. It was the purpose of this work to design and implement such an instrument. This instrument should deliver real-time data for material displacement during forming, which can then be used to better understand material plastic response and formability. Four different subsystems within this mechanism must interact, but also have enough independence for analysis and for assembly purposes. The combined sub-systems produced a GPBF apparatus capable of forming a sheet aluminum alloy AA5182 with a thickness of 1.5 mm into a dome with a height nearly equal to its radius under a constant gas pressure as low as 40 psi at 450°C. This GPBF apparatus produced, for the first time, in-situ data for dome peak displacement during gas-pressure bulge forming of AA5182 sheet at 450°C. / text

Aluminum alloys are a suitable substitution for heavy ferrous alloys in automobile structures. The purpose of this study was to investigate the flow stress behavior of as-cast and homogenized A535 aluminum alloy under various deformation conditions. A hot compression test of A535 alloy was performed in the temperature range of 473-673 K (200-400˚C) and strain rate range of 0.005-5 s-1 using a GleebleTM machine. Experimental data were fitted to Arrhenius-type constitutive equations to find material constants such as n, nʹ, β, A and activation energy (Q). Flow stress curves for as-cast and homogenized A535 alloy were predicted using an extended form of the Arrhenius constitutive equations. The dynamic shock load response of the alloy was studied using a split Hopkinson pressure bar (SHPB) test apparatus. The strain rate used ranged from 1400 s-1 to 2400 s-1 for as-cast and homogenized A535 alloy. The microstructures of the deformed specimens under different deformation conditions were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). Obtained true stress-true strain curves at elevated temperatures showed that the flow stress of the alloy increased by increasing the strain rate and decreasing the temperature for both as-cast and homogenized specimens. The homogenization heat treatment showed no effect on the mechanical behavior of the A535 alloy under hot deformation conditions. Hot deformation activation energy for both as-cast and homogenized A535 alloy was calculated to be 193 kJ/mol, which is higher than that for self-diffusion of pure aluminum (142 kJ/mol). The calculated stress values were compared with the measured ones and they showed good agreement by the correlation coefficient (R) of 0.997 and the average absolute relative error (AARE) of 6.5 %. The peak stress and the critical strain at the onset of thermal softening increased with strain rate for both the as-cast and homogenized A535 alloy. Homogenization heat treatment affected the high strain-rate deformation of the alloy, by increasing the peak stress and the thermal softening onset strain compared to those obtained for as-cast specimens. Deformed shear bands (DSBs) were formed in both the as-cast and homogenized A535 alloy in the strain rate range of 2000-2400 s-1.

An experimental and numerical study of the isothermal and non-isothermal warm formability of an AA3003 aluminum alloy brazing sheet is presented. Forming limit diagrams were determined using warm limiting dome height (LDH) experiments with in situ strain measurement based on digital image correlation (DIC) techniques. Forming limit curves (FLCs) were developed at several temperature levels (room temperature, 100ºC, 200ºC, 250ºC, and 300ºC) and strain-rates (0.003, 0.018, and 0.1s-1). The formability experiments demonstrated that temperature has a significant effect on formability, whereas forming speed has a mild effect within the studied range. Elevating the temperature to 250C improved the formability more than 200% compared to room temperature forming, while forming at lower speeds increased the limiting strains by 10% and 17% at room temperature and 250ºC, respectively. Non-isothermal deep draw experiments were developed considering an automotive heat exchanger plate. A parametric study of the effects of die temperature, punch speed, and blank holder force on the formability of the part was conducted. The introduction of non-isothermal conditions in which the punch is cooled and the flange region is heated to 250C resulted in a 61% increase in draw depth relative to room temperature forming. In order to develop effective numerical models of warm forming processes, a constitutive model is proposed for aluminum alloy sheet to account for temperature and strain rate dependency, as well as plastic anisotropy. The model combines the Barlat YLD2000 yield criterion (Barlat et al., 2003) to capture sheet anisotropy and the Bergstrom (1982) hardening rule to account for temperature and strain rate dependency. Stress-strain curves for AA3003 aluminum alloy brazing sheet tested at elevated temperatures and a range of strain rates were used to fit the Bergstrom parameters, while measured R-values were used to fit the yield function parameters. The combined constitutive model was implemented within a user defined material subroutine that was linked to the LS-DYNA finite element code. Finite element models were developed based on the proposed material model and the results were compared with experimental data. Isothermal uniaxial tensile tests were simulated and the predicted responses were compared with measured data. The tensile test simulations accurately predicted material behaviour. The user material subroutine and forming limit criteria were then applied to simulate the isothermal warm LDH tests, as well as isothermal and non-isothermal warm deep drawing experiments. Two deep draw geometries were considered, the heat exchanger plate experiments developed as part of this research and the 100 mm cylindrical cup draw experiments performed by McKinley et al. (2010). The strain distributions, punch forces and failure location predicted for all three forming operations were in good agreement with the experimental results. Using the warm forming limit curves, the models were able to accurately predict the punch depths to failure as well as the location of failure initiation for both the isothermal and non-isothermal deep draw operations.

Les pièces en aluminium sont largement utilisées dans le domaine aéronautique en raison de leurs bonnes propriétés mécaniques. Mais elles nécessitent un traitement de surface pour améliorer leur tenue en corrosion. Soumises à de nouvelles normes sur l'utilisation de produits chimiques et à la prise de conscience de la protection environnementale et humaine, les industries aéronautiques doivent à présent impérativement remplacer les procédés de traitements de surface actuels, devenus obsolètes car incluant des composés CMR. L'objectif de ces travaux de recherche est de développer un traitement de surface par voie liquide, à la fois innovant et conforme à la législation REACH, pour améliorer les propriétés d'anticorrosion des alliages d'aluminium ; le procédé d'élaboration présentement étudié, est composé d'une anodisation poreuse puis d'un colmatage par imprégnation de particules au sein des pores. Un film anodique poreux " modèle " a tout d'abord été élaboré et caractérisé : son épaisseur est de 10 µm, tandis que les pores sont rectilignes et ont un diamètre moyen de 120 nm. Puis, nous avons étudié la synthèse par voie aqueuse, de nanoparticules de boehmite, l'optimisation des différents paramètres de synthèse ayant permis finalement d'obtenir des particules d'une taille inférieure à celle des pores du film anodique. Deux techniques d'incorporation ont ensuite été expérimentées : le trempage-retrait et l'électrophorèse. La compréhension des mécanismes mis en jeu et de l'influence de différents paramètres opératoires, a permis une maitrise des procédés et l'insertion effective de particules. Des caractérisations microstructurales ont en particulier montré que l'insertion de particules est plus aisée dans le cas d'une électrophorèse avec une tension pulsée. Enfin, la mise en œuvre d'un post-traitement hydrothermal après l'imprégnation, a permis d'obtenir un colmatage complet des pores du film anodique, et d'augmenter significativement les propriétés anticorrosion. / Aluminum parts are widely used in the aeronautical field because of their good mechanical properties. But they require a surface treatment to improve their resistance to corrosion. Subject to new standards on the use of chemicals and awareness of environmental and human protection, the aeronautical industry must now replace current surface treatment processes, which have become obsolete because they include CMR compounds. The aim of this research is to develop a surface treatment, both innovative and REACH compliant, to improve the anticorrosion properties of aluminum alloys; the process here studied, is composed of a porous anodization and a sealing by impregnation of particles within the pores. A "model" porous anodic film was first prepared and characterized: its thickness is 10 µm, while the pores are straight and have a mean diameter of 120 nm. Then, we studied the aqueous synthesis of boehmite nanoparticles; the optimization of the synthesis parameters finally allowed to obtain a particle size smaller than the pore diameter. Two incorporation techniques were then tested: dip-coating and electrophoresis. The understanding of the involved mechanisms and of the influence of different operating parameters, allowed a control of the processes and the effective insertion of particles. In particular, microstructural characterizations showed that the particle insertion is easier using pulsed voltage electrophoresis. Finally, a hydrothermal post-treatment after the impregnation, allowed to obtain a complete sealing of the anodic film pores, and to significantly increase the anticorrosion properties.

Orientador: Rodnei Bertazzoli / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica, Faculdade de Engenharia Eletrica e de Computação e Instituto de Quimica / Made available in DSpace on 2018-08-15T03:56:41Z (GMT). No. of bitstreams: 1 Costa_RegisSilvada_M.pdf: 2450991 bytes, checksum: d60e53258406b167bb36e4bd6cce3a71 (MD5) Previous issue date: 2009 / Resumo: A presente dissertação de mestrado tem por objetivo o estudo do fenômeno de corrosão entre dois componentes do motor de combustão interna, ciclo Diesel, caixa de distribuição (liga de alumínio AA A380.0) e bloco de cilindros (ferro fundido cinzento), bem como o estudo de alternativas para minimização desta corrosão. Foram utilizados métodos de medição de diferença de potencial galvânico, caracterização de materiais e medições de perda de massa. A liga de alumínio que atualmente é utilizada na caixa de distribuição apresenta maior diferença de potencial com o bloco de cilindros quando comparada às demais ligas de Al que foram ensaiadas com o bloco de cilindros, com a diferença de potencial em torno de 200 mV. Possui maior susceptibilidade à corrosão galvânica com o bloco de cilindros, agindo como anodo no par galvânico. A liga AA 413 possui menor diferença de potencial (150 mV) no par galvânico com o bloco de cilindros de ferro fundido cinzento, em comparação com a liga AA A380.0, possuindo semelhante resistência mecânica. As ligas AA 410, 5052 e 1100, foram as ligas que apresentaram menor diferença de potencial com o bloco de cilindros, em torno de 45 mV. Com a passivação da liga AA A380.0 em solução polimérica, a diferença de potencial diminuiu para 165 mV. Pelo ensaio de perda de massa da liga A380.0, sem par galvânico, obteve-se a densidade de corrente e taxa de corrosão, e por consequência a perda de massa da caixa de distribuição estimada para 300.000 km que foi de 7 g. O ensaio de perda de massa da liga AA A380.0 com formação de par galvânico com o bloco de cilindros, possibilitou estimar a perda de massa por corrosão para a caixa de distribuição com 300.000 km que ficou em torno de 100 g, evidenciando a severidade da corrosão galvânica na caixa de distribuição no par galvânico com o bloco de cilindros. Para a liga AA A380.0 passivada em solução polimérica a perda de massa estimada para a caixa de distribuição com 300.000 km ficou em torno de 36 g e para a liga AA 413 ficou em torno de 57 g. Para ambas ligas uma melhora significativa na resistência à corrosão, quando comparado à liga AA A380.0 / Abstract: The present investigation has for purpose the study of the corrosion phenomenon between two components of Diesel engine, timing case (aluminum alloy AA A380.0) and crankcase (grey iron casting), and the study of alternatives for the decreasing of this corrosion. Measurement methods of potential galvanic difference, materials characterization and mass loss measurements had been used. The aluminum alloy that is currently used in the timing case presents greater potential difference with the crankcase when compared with the other Al alloys that was tested with the crankcase, with the potential difference around 200 mV. It has greater feasibility to the galvanic corrosion with the crankcase, acting as anode in the galvanic couple. AA 413 alloy presents lower potential difference (150 mV) in the galvanic couple with the crankcase, in comparison with AA A380.0 alloy. AA 410, 5052 and 1100 alloys, had been the alloys that had presented minor potential difference with the crankcase, around 45 mV. With the AA A380.0 protection in polymeric solution, the potential difference decreased to 165 mV. By the mass loss measurements AA A380.0 alloy, without galvanic couple, it was gotten chain density and corrosion rate, and consequently the mass loss of timing case appraised for 300.000 km that was around 7 g. Through the mass loss measurements AA A380.0 alloy, with formation of galvanic couple with crankcase, made possible appraise the corrosion mass loss for the timing case with 300,000 km that was around 100 g, evidencing the severity of the galvanic corrosion in the timing case in the galvanic couple with crankcase. For AA A380.0 alloy passivated in polymeric solution the mass loss appraised for timing case with 300,000 km was around 36 g and for AA 413 alloy it was around 57 g. For both alloys a significant improvement in the corrosion resistance, when compared with AA A380.0 alloy / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Automobilistica