Dissertationen zum Thema „T6 heat treatment“

Published Article
The heat treatment cycles that are currently applied to semi-solid processed components are mostly those that are in use for traditional dendritic alloys. These heat treatments are not necessarily the optimum heat treatments for SSM processing. The T6 heat treatment of aluminium alloys is a relatively expensive process and a reduction in treatment times would be advantageous. In order to improve the T6 heat treatment cycle for rheocast alloy A356, the effect of various parameters on the quality index were investigated. These included solution treatment time, natural aging time, artificial aging temperature and artificial aging time.

Aluminum alloys are having more attention due to their high specific stiffness and processing advantages. 7075 aluminum alloy is a wrought composition aluminum alloy in the Al-Zn-Mg-Cu series. Due to the significant addition of these alloying elements, 7075 has higher strength compared to all other aluminum alloys and effective precipitation hardenability characteristic. On the other hand, aluminum alloys have some drawbacks, which hinder the widespread application of them. One of the most commonly encountered defects in aluminum alloys is the hydrogen porosity. Additionally, in case of 7075, another problem is the lack of fluidity. Magnesium addition is thought to be effective in compensating this deficiency. Accordingly, in this study, die cast 7075 aluminum alloy samples with hydrogen porosity and additional magnesium content were investigated. The aim was to determine the relationship between hydrogen content and hydrogen porosity, and the effects of hydrogen porosity, additional magnesium and T6 heat treatment on ultimate tensile and flexural strength properties of pressure die cast 7075 aluminum alloy. 7075 aluminum alloy returns were supplied from a local pressure die casting company. After spectral analysis, pressure die casting was conducted at two stages. In the first stage, 7075 aluminum alloy with an increase in magnesium concentration was melted and secondly 7075 aluminum alloy was cast directly without any alloying addition. While making those castings, hydrogen content was measured continuously before each casting operation. As a final operation T6 heat treatment is carried out for certain samples. Finally, in order to accomplish our aim, mechanical and microstructural examination tests were conducted.

O objetivo desse trabalho é analisar a fabricação de buchas a base de Alumínio empregando o processo de Metalurgia do Pó, em substituição ao processo atual de fundição e usinagem. O material testado é uma liga a base de Alumínio AlSi10Cu3, essa liga contem 87% de Alumínio, 10% de Silício, 2,5% de Cobre, 0,25% de Magnésio e Manganês, conforme a norma DIN EN 1706. As amostras foram compactadas à 600MPa, resultado obtido da curva de compressibilidade. As amostras foram sinterizadas a uma temperatura de 550ºC durante 60 minutos. Após sinterização as amostras foram submetidas ao processo de Tratamento Térmico T6, com temperatura de solubilização de 480°C por 5 horas e envelhecimento a 220°C por 5 horas, nomeado Tratamento Térmico A. Foram realizados ensaios de densidade, dureza, metalografia, compressibilidade, difração de raios-x e variação dimensional. A densidade das amostras sinterizadas atingiram 2,52 g/cm3 ± 0,25. A dureza superficial das amostras atingiram uma média de 51 HB ± 4. Com o tratamento térmico T6 a dureza elevou-se para 74 HB ± 2. A variação dimensional das amostras após sinterização foi de 0,20% na área dos corpos de prova. Foram estudadas também diferentes composições químicas para elevar a dureza superficial. Executou-se um teste com outros parâmetros de Tratamento Térmico T6 para aumento da dureza, chamado de Tratamento Térmico B, com parâmetros de temperatura de solubilização de 550°C por 1 hora e envelhecimento com 160°C por 18 horas.
The objective of this work is to analyze the manufacture of aluminum based bushings employing the Powder Metallurgy process in substitution of the current process of casting and machining. The material tested is an AlSi10Cu3 aluminum alloy, this alloy contains 87% aluminum, 10% silicon, 2.5% copper, 0.25% magnesium and manganese, according to DIN EN 1706. The samples were pressed at 600MPa, result obtained from the compressibility curve. The samples were sintered at a temperature of 550°C for 60 minutes. After sintering, the samples were submitted to the T6 Thermal Treatment process, with a solubilization temperature of 480°C for 5 hours and aging at 220°C for 5 hours, named Thermal Treatment A. Density, hardness, metallography, compressibility, X-ray diffraction and dimensional variation testings were performed. The density of the sintered samples reached 2.52 g/cm3 ± 0.25. The surface hardness of the samples reached the mean of 51 HB ± 4. With the heat treatment T6 the hardness increased to 74 HB ± 2. The dimensional variation of the samples after sintering was 0.20% by area. Different chemical compositions were also studied to raise the surface hardness. A test was performed with other parameters of T6 Thermal Treatment to increase the hardness, called Thermal Treatment B, with parameters of solubilization temperature of 550°C for 1 hour and aging with 160°C for 18 hours.

O objetivo deste trabalho foi de otimizar o processo de fabricação da placa reforçadora de solo, fabricada pelo processo de injeção sob baixa pressão em liga de alumínio. Atualmente, a liga utilizada no processo é a SAE 305 (AA 413) e problemas de falha do componente em campo tem sido reportados pelos clientes. As peças estudadas referem-se às placas acessórias utilizadas para fornecer sustentação durante a entrada e saída de vaus por carros de combate do Exército Brasileiro, anteriormente adquiridas no mercado internacional e agora produzidas internamente. O estudo focou na alteração da composição química da liga, baseado na liga de alumínio da peça importada, tratamento de banho com modificação do silício, refino de grão e modificação no projeto do molde permanente. Adquiriu-se junto ao fornecedor a liga de Al9Si0,3Mg visando a fabricação das peças com tratamento térmico T6. Para obtenção das propriedades mecânicas foram realizados ensaios de tração, dureza Brinell e impacto. Para caracterização metalúrgica foram realizados ensaios metalográficos com auxílio de microscopia óptica. Verificou-se que a presença de magnésio na liga Al-Si exclusivamente com tratamento térmico T6, alterou o comportamento mecânico da peça melhorando seus resultados. O tratamento de banho com modificador de silício a base de sódio não produziu resultados significativos. Finalmente, realizou-se simulação do preenchimento da molde via software CAE Click2Cast, modo injeção de baixa pressão, para caracterização dos defeitos e sugestões de melhoria no sistema de alimentação. Deste trabalho, conclui-se que as melhores propriedades mecânicas de resistência a tração e dureza foram obtidas com a alteração da liga SAE 305 para a liga Al9Si0,3Mg com tratamento térmico T6 e que para atingir melhores resultados deve-se introduzir ao processo um novo molde permanente com refrigeração e alimentação adequada da peça.
The objective of this research was to optimize the manufacturing process of the reinforcing plate of soil, manufactured by the injection process under low pressure in Al-Si alloy. Currently, the alloy used in the process is SAE 305 (AA 413) and mechanical resistance problems, when used in the field, have been reported by customers. Currently, the alloy used in the process is SAE 305 (AA 413) and field component failure problems have been reported by customers. The studied pieces refer to the accessory plates used to provide support during the entry and exit of vats by tanks of the Brazilian Army, previously acquired in the international market and now produced internally. The study focused on the alteration of the chemical composition of the alloy, based on the aluminum alloy of the imported part, bath treatment with silicon modification, grain refining and modification in the permanent mold design. The Al9Si0.3Mg alloy was purchased from the supplier to manufacture the T6 heat treated parts. To obtain the mechanical properties tensile tests, Brinell hardness and impact were performed. For metallurgical characterization, metallographic tests were performed with the aid of light microscopy. It was verified that the presence of magnesium in the Al-Si alloy exclusively with T6 heat treatment, altered the mechanical behavior of the part improving its results. Bath treatment with sodium silicon modifier did not produce significant results. Finally, the mold filling simulation was carried out using CAE Click2Cast software, low pressure injection mode, to characterize the defects and suggestions for improvement in the feed system. From this work, it was concluded that the best mechanical properties of tensile strength and hardness were obtained with the change of the SAE 305 alloy to the Al9Si0.3Mg alloy with T6 thermal treatment and that to achieve better results a new permanent mold with cooling and proper feeding of the part.

The presented diploma thesis deals with various types of quenching and their respective effects on mechanical and structural properties of AlSi7Mg0.6 alloy castings. Cast with precision casting technology into a self-supporting ceramic shell made by plaster investment technology, flat test bars cast by Alucast were used as experimental samples. Sample castings were used in both cast state and after T6 heat treatment. Air-flow and air-water combination with varying water passage (spraying) were used as the quenching media in the quenching process of the castings. In order to evaluate the effect of five different quenching processes on the structure and mechanical properties of the castings, the method of light microscopy, Brinell hardness test and static traction test were used. Evaluation and porosity and SDAS quantifications were carried out by means of image analysis. Experiments did not prove right the hypothesis holding that low SDAS values inevitably mean higher mechanical properties of the castings. On the other hand, distinct is the negative influence of heterogeneous structure and porosity. Despite the fact that the heat treatment was successful in reducing the influence of structural inhomogeneities, it cannot be concluded that spray quenching has an utterly positive bearing on the mechanical and structural properties of the castings.

Ce travail montre l'impact des défauts et de la microstructure sur la limite de fatigue de l’AlSi10Mg de fabrication additive (FA). Les échantillons d’étude sont fabriqués suivant trois orientations (0 °, 45 ° et 90 °) ; les surfaces d’étude sont usinées ou brutes de fabrication. Les éprouvettes sont étudiées avec ou sans traitement thermique T6. Avant toute chose, le matériau est d’abord caractérisé en lien avec les paramètres du procédé à l’aide de plusieurs moyens (microscopie, microtomographie). Du point de la fatigue, les courbes S-N sont établies avant et après T6, principalement à R = -1 en sollicitation uniaxiale. Pour toutes les éprouvettes d’étude, l’analyse des faciès montre que ce sont toujours les défauts qui sont à l’origine de la rupture par fatigue. Ainsi, un critère est appliqué pour définir ces défauts critiques (type, taille morphologie et position) et la limite de fatigue est systématiquement analysée via les diagrammes de Kitagawa. Le rôle de la direction de construction sur la tenue en fatigue est étudié, avant et après traitement thermique T6, tant pour les surfaces usinées que brutes de fabrication. À cet effet, un scénario basé sur la taille caractéristique des grains est proposé pour expliquer les effets d’orientation post-T6. La contribution de la structure de précipitation est également étudiée ; ainsi que le rôle des défauts (type, taille, morphologie et position) sur la limite de fatigue à différents états microstructuraux : avant et après T6. Afin de comprendre les mécanismes d’endommagement par fatigue en surface, la méthode des répliques est déployée sur une éprouvette polie. Dans ce cadre, une loi de propagation des fissures naturelles, c'est-à-dire qu'elles sont dues à un défaut hérité du procédé, est identifiée. Elle permet de séparer les phases d’amorçage et de propagation, alimentant ainsi les discussions sur les phénomènes d’amorçage en présence de défauts. Par ailleurs, quelques critères de fatigue sont également discutés et l’approche Defect Stress Gradient (DSG) est adaptée au matériau d’étude en tenant compte de la taille des grains cristallographiques. Pour les sections utiles brutes de fabrication, le rôle du mode de suppression des supports fabrication sur l’amorçage des fissures de fatigue est étudié ; la définition de la notion de taille de défauts en présence de la rugosité, à l’échelle de l’ondulation de surface, est abordée. Sachant que l’amorçage peut avoir lieu sur une ondulation de surface ou sur un défaut isolé (porosité ou défaut de fusion), une méthode expérimentale est proposée pour analyser la compétition entre ces facteurs. Dans un contexte de développement industriel, l’influence sur la limite de fatigue des paramètres de procédé relatifs au laser (vitesse de balayage, puissance et distance de hachure), au lit de poudre (composition chimique, taille des particules, épaisseur du lit) est étudiée, en vue d’alimenter les discussions vers l’optimisation du procédé du point de vue de la tenue en fatigue
This work shows the impact of defects and microstructure on the fatigue limit of AlSi10Mg produced by Additive Layer Manufacturing (ALM). Samples are produced according to three orientations with respect to the construction plate (0 °, 45 ° and 90 °); the studied surfaces are machined or left as-built (AB) in the gauge section. The specimens are studied with or without T6 heat treatment. The study surfaces are machined or as built. Some specimens are subjected to T6 heat treatment. Before any others study, the material is characterized in connection with the process parameters through several techniques (microscopes and 3D X-ray microtomography). Regarding the fatigue, the S-N curves are established before and after T6, mainly at R = -1 under uniaxial loading. For all the fatigue test specimens, fracture surfaces analysis shows that it is always a defect that cause fatigue failure. Thus, a criterion is applied to define these critical defects (type, size morphology and position) and the fatigue limit is analyzed through the Kitagawa type diagrams. The role of the building direction on the fatigue strength is studied, before and after T6 heat treatment, for both machined and as-built surfaces. For this purpose, a sketch based on the characteristic grain size is proposed to explain post-T6 orientation effects. The contribution of the precipitation structure is also studied; as well as the role of defects (type, size, morphology and position) on the fatigue limit at different microstructural states: before and after T6. In order to understand the surface fatigue damage mechanisms, the replica method is used on a polished specimen. In this context, a propagation law of natural cracks, that is to say due to a defect inherited from the process, is identified. It makes it possible to separate the initiation and propagation phases, thus feeding the discussions on the phenomena of priming in the presence of defects. In addition, some fatigue criteria are also discussed and the Defect Stress Gradient (DSG) approach is adapted to the studied material, by taking into account the size of the crystallographic grains. In the specific case of specimens with as-built useful sections, the role of the process of suppression of the building supports on the initiation of fatigue cracks is studied; the definition of the concept of defect size in the presence of roughness, at the scale of the surface undulation, is discussed. Knowing that initiation can occurs on a surface undulation or on an isolated defect (porosity or lack-of-fusion), an experimental method is proposed to analyze the competition between these factors. In a context of industrial development, the influence on the fatigue limit of the process parameters, related to the laser (scanning speed, power and hatching distance), or powder bed (chemical composition, particle size, bed thickness) is studied, in order to feed the discussions towards the process optimization regarding the fatigue strength

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Aluminum alloys have been the primary material of choice for the aircraft due to their properties such as low density, high mechanical and corrosion resistance. Commercial aircraft apply aluminum alloys for the fuselage, wings and supporting structure due to the extensive knowledge in design and production of aluminum components, and most importantly, aluminum alloys continue to be developed, keeping it highly competitive. A great development happen with the heat-treatable alloys, which allow improvement of the mechanical properties. Among this alloys stand out the Al-Zn-Mg-Cu series, known for high strength, toughness and corrosion resistance. The improvement of those alloys occurs by the precipitation of nanometric particles MgZn2, called η phase. This study’s aim was to promote an interrupted heat treatment T6I4-65 in an AA7050 aluminum alloy, with fatigue crack growth resistance as priority. Interrupted heat treatments’ goal is optimizing the consumption of solute atoms during process of nucleation and growth of precipitates as a finely dispersion. The T6I4-65 condition obtained was analyzed by differential scanning calorimetry, DSC, optical and electronic microscopy, mechanical tests as hardness, tensile and fatigue crack growth. The T6I4-65 treatment results in a microstructure with a fine dispersion of precipitated phase η’, about 75% smaller than those resulting from in current use, T7451. This microstructure resulted in a reduction of up to 24% in fatigue crack growth rate compared to that resulting from T7451 treatment, keeping the ductility of 17% of area reduction and yield strength higher than 400MPa.
Ligas de alumínio são o principal material de uso na indústria aeronáutica devido a suas propriedades como baixa densidade, alta resistência mecânica e a corrosão. Aeronaves comerciais utilizam ligas de alumínio em sua fuselagem, asas e na estrutura de suporte devido ao extenso conhecimento no projeto e produção de componentes em alumínio, e mais importante, as ligas de alumínio continuam a serem desenvolvidas, mantendo-se altamente competitivas. Ocorreu um grande avanço com o desenvolvimento das ligas tratáveis termicamente, que permitiram a otimização das propriedades mecânicas. Entre estas ligas tratáveis, destaca se a família Al-Zn-Mg-Cu, conhecidas pela alta resistência mecânica, tenacidade e resistência a corrosão. O aperfeiçoamento destas ligas ocorre pela precipitação de partículas nanométricas de MgZn2, conhecida como fase η. O objetivo deste trabalho foi obter um tratamento térmico interrompido T6I4-65 em uma liga de alumínio AA7050 com prioridade ao aumento de resistência à propagação de trinca por fadiga. Tratamentos interrompidos tem por objetivo otimizar o consumo de átomos de soluto durante os processos de nucleação e crescimento dos precipitados endurecedores na liga na forma de dispersão finamente dispersa. A condição T6I4-65 obtida foi analisada por meio de calorimetria diferencial de varredura, DSC, microscopia ótica e eletrônica de varredura e transmissão, ensaios mecânicos dureza, tração e propagação de trinca por fadiga. Este tratamento resultou em uma microestrutura com uma dispersão de finos precipitados de fase η’, cerca de 75% menores que os resultantes de tratamentos de uso corrente, T7451. Esta microestrutura promoveu a redução de até 24% na taxa de propagação de trinca por fadiga em comparação à resultante do tratamento T7451, mantendo grande ductilidade, até 17% de redução de área e limite de escoamento superior a 400MPa.

博士
崑山科技大學
機械與能源工程研究所
106
Damage caused by the mechanical parts caused by wear and tear always seriously affect the accuracy of machinery. Hence, it is necessary to improve the material properties of the mechanical elements for mechanical engineers. Furthermore, low friction plays an important role in saving energy. It is important to establish a key technology for wear resistance and low friction through appropriate materials science for related industries. In general, the tribological properties of aluminum alloys are very different from those of steels. Hence, aluminum alloys should be specially considered and clarified for their tribological properties before being applied industrially. This paper therefore aims to further investigate the effects of the content of doping elements on the friction and wear of the selected aluminum alloys. Moreover, effects of T6 heat treatment on Tribological properties are also investigated. From the experimental results, it can be concluded that the higher the silicon content, the smaller the friction coefficient. The higher the content of iron and copper, the more materials are removed, showing better machinability. Moreover, three frictional models and wear mechanisms that describe the effects of the content of doping elements on the friction and wear are proposed. The wear mechanisms change as the silicon content increases, from the junction growth to the wedge and the ploughing particles. By the three models, better choices of aluminum alloys with regards to friction and wear can then be made. These results have great practical importance.

碩士
國立臺灣海洋大學
機械與機電工程學系
106
Cast aluminum alloy has good mechanical properties such as strength, hardness…etc, and has the characteristics of light weight. But its components contain with silicon, copper, magnesium and other elements that produced into the compound makes casting ductility poor. Therefore, most of the castings are generally considered that cannot be applied in the application of high breakdown strength, majority application are applied in the appearance of the pieces. The current method to increase the strength of castings is using heat treatment, but it’s not really effectively to enhance the strength and ductility of the casting. In this research used A356 to be the base material. The 0wt%-1wt% of manganese, 0wt%-5wt% of zinc and 0wt%-0.1wt% of strontium add into melt while casting. After manufacturing into ingots, treat with multiple heat treatment to increase the mechanical properties including tensile property, hardness and ductility. The condition of heat treatment included solution treatment with 520°C in twice continuously, quenching before ageing treatment with 170°C, 720 minutes. Two ways of studying after heat treatment, one is about the mechanical properties testing including tensile properties, hardness and ductility. Another is about the microstructure observation. Using the polishing equipment and keller’s reagent to displayed the microstructure of alloy under high magnification microscope. From the experimental results, it is found that the casting with the addition of 0.2wt% of manganese, 5wt% of zinc and 0.03wt% of strontium for 6 hours in T6 heat treatment is the best with the strength of 278.6MPa and the ductility of 3.27%. The hardness can be up to 104.5HBW, the strength can be increased by about 9%, the hardness can be increased by 23% and the ductility by about 34% compared with the A356-T61 alloy.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
Esta dissertação de mestrado tem por objetivo estudar a influência das condições de tratamento térmico T6 na recuperação das características mecânicas da soldadura, perdidas devido ao processo de soldadura Cold Metal Transfer, na liga AA6061. Este estudo pretende contribuir para a otimização do processo industrial de produção de quadros de bicicleta da empresa Triangle’s.Quadros de bicicleta, produzidos nas atuais condições de fabrico, foram fornecidos pela empresa Triangle’s Cycling Equipment, S.A.. No atual processo produtivo, a matéria-prima é fornecida no estado tratado T4, submetida a deformação plástica por extrusão ou hidroformação, soldada por soldadura Cold Metal Transfer com fio de adição AA4043 e tratada termicamente. Com o objetivo de recuperar as propriedades mecânicas perdidas em todo o processo, estes quadros são submetidos a um tratamento térmico complexo, por forma a obter o estado de tratamento T6.Foram comparados os tempos e temperaturas deste tratamento com resultados obtidos em trabalhos anteriores, de forma a avaliar o progresso do processo produtivo da empresa. Foi também avaliado o comportamento mecânico do material base quando submetido a tratamento similar.Dos dois quadros analisados com parâmetros de tratamento térmico iguais, um deles revelou pior comportamento à tração, e ambos obtiveram valores de microdureza e resistência à tração inferiores aos quadros da mesma empresa estudados em trabalhos anteriores, mas com diferentes parâmetros de tratamento térmico. Algumas soldaduras revelaram diluição deficiente de Magnésio na Zona Fundida e, consequentemente, má recuperação dos valores de microdureza.
The goal of this master’s dissertation is to evaluate the influence of the time and temperature used in the heat treatment on the recovery of mechanical properties lost under the Cold Metal Transfer welding process, in the AA6061 alloy. This study intends to contribute to optimize the industrial process of production of bicycle frames of Triangle's company.Bicycle frames, fabricated in the current production conditions, were provided by Triangle’s Cycling Equipment, S.A.. In the current production process, raw material arrives at the plant in the T4 state, being subjected to plastic deformation by extrusion or hidroforming, welded by Cold Metal Transfer with an AA4043 filler wire and finally heat-treated. With the purpose of recovering the mechanical properties lost in this process, these bicycle frames are subjected to a complex heat treatment, in order to obtain the T6 treated state.Times and temperatures of this treatment were compared to results obtained in previous experiments, to evaluate the company’s productive progress. It was also evaluated the mechanical behavior of the base material submitted to the same treatment.Out of the two studied frames with the same heat treatment parameters, one of them revealed poor tensile behavior, and both obtained inferior microhardness and tensile strength values in comparison to frames of the same company, studied in previous investigations, but with different heat treatment parameters.Some welded joints revealed poor Magnesium dilution in the Melted Area and, as a consequence, poor recovery of the microhardness values.

碩士
國立虎尾科技大學
材料科學與綠色能源工程研究所
103
Equal channel angular extrusion (ECAE) is a shear strain process of metal. ECAE mold has an equal cross-section channel with constant corner angle, an external force is applied to the metal through this channel to produce a homogenous and severe plastic deformation, extruded bulk metal will produce high flow stress due to metal flow at the corner, however the cross-section area of channel remains unchanged, the metal can be extruded continuously to accumulate large shear strain and causes grain refinement result, the hardness and the strength of metal can be increased, and elongation also can be improved. In this study, the pre-experiment was conducted to find a suitable extruded temperature for 7075 aluminum alloy. The multi-pass extrusion and T6 treatment were carried out at a fixed extrusion route to reveal the effect of extrusion parameters and process methods on mechanical properties and microstructures for extruded aluminum alloy samples by changing these parameters (temperature, passes) and process methods (solid solution treatment, quenching and extruded order); and also to compare the advantages and disadvantages of different process methods. The effect of strain on recrystallization and precipitation hardening was also revealed, and finally we demonstrated that the mechanical properties of the material can be improved through ECAE process. The experiment results show that annealed and solution-heat-treated 7075 aluminum alloy samples should be extruded at a minimum temperature of 165oC while they can be successfully carried out 12 passes ECAE process, and also achieve the result of strain hardening. The lower is the extrusion temperature, the higher will be the strengthening result obtained; the higher is the extrusion temperature, the better will be the elongation result. The samples which were conducted the ECAE (165oC or 205oC) process using extrusion route BC will obtain the highest elongation in 12 passes extrusion, and surface hardness of each side on extruded samples will achieve uniformity. Annealed samples were extruded by ECAE process at 165 oC and 205 oC, when the extrusion pass increases, both hardness and tensile strength of the samples present different variation tendency; but the elongation of the samples presents a minimum values at 4 passes extrusion and a maximum values at 12 passes extrusion. Annealed sample was extruded by ECAE process at 165 oC and T6 treatment, the higher is the extrusion pass, the shorter will be the aging time which gets peak hardness, but the higher the hardness value. The extruded sample with more extrusion passes gets the smaller grain size, the grains of sample with 12 extrusion passes show uniform equiaxed shape, ASTM grain size number is about 6. While solution-heat-treated 7075 aluminum alloy samples were extruded by ECAE process at 165 oC and subsequently artificially aged at 120 oC, the higher is the extrusion pass, the shorter will be the aging time which gets peak hardness, but the lower the hardness value; and vice versa. The solution-heat-treated samples which were extruded through 2 and 4 passes ECAE process at 165 oC and followed by peak artificial aging treatment can significantly improve the strength and hardness, the increment in strength and hardness for these samples is larger than that of samples which were solution-heat-treated and subsequently ECAE process at 165 oC and annealed then only through T6 (peak aging) treatment, and there is no loss on ductility. The strength and hardness of solution-heat-treated sample which was quenched and followed by 2 passes ECAE process at 165oC and peak artificially aged is almost equal to that of samples which was extruded through 12 passes ECAE process at 165oC and T6(peak artificially aged) treatment.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
The work carried out within this dissertation aimed the study of the influence of the process parameters, and of the tool geometry, on the properties of 7075-T6 lap welds produced by Friction Stir Welding (FSW). Two different tools, one with a cylindrical pin and another with a three-faceted cylindrical pin, were used in the investigation. Two different combinations of welding and rotational speeds (welding-pitch) were used for each tool. The welds were tested in two different post-welding conditions: as-welded and heat-treated (solubilisation at 480ºC for 2 hours).The characterization of the welds included performing metallographic analysis, hardness tests and shear-tensile tests of retreating side samples. The shear-tensile tests were performed using monotonic loading, for samples in both post-welding conditions, and cyclic loading, for samples in the as-welded condition. The metallographic analysis revealed the presence of the Hook defect, at the advancing side, and of the Cold Lap Defect, at the retreating side of all the welds. Differences in Nugget morphology, for the welds produced with different welding pitches, were also registered. In spite of this, no important differences in welds strength in monotonic loading were found, for the samples in both post-welding conditions. Only the failure mode of the welds in the heat-treated condition was found to be different for the welds performed with the different welding-pitches. The metallographic analysis revealed the occurrence of abnormal grain growth (AGG), in the entire Nugget region, during the solubilization treatment. A close relation between the abnormal grain size and morphology, inside the Nugget, and the failure mode in monotonic loading was found. It was also found that Nugget microstructure should had influence on the fatigue strength of the welds. In fact, the welds produced with higher welding pitch, with smaller grain size in the Nugget, had higher fatigue strength than the welds produced with smaller welding pitch.
O trabalho realizado no âmbito desta dissertação teve por objetivo analisar a influência dos parâmetros do processo Fricion Stir Welding (FSW), e da geometria da ferramenta, nas propriedades de soldaduras produzidas, em junta sobreposta, na liga de alumínio tratável termicamente 7075-T6. Para tal utilizaram-se duas ferramentas distintas, uma com pino cilíndrico e outra com pino cilíndrico tri-facetado, e foram testadas duas combinações de velocidades de avanço e de rotação distintas, para cada ferramenta. As soldaduras foram ensaiadas em duas condições de tratamento: após soldadura e após tratamento térmico de solubilização.O trabalho de caracterização das soldaduras compreendeu a realização de testes de análise metalográfica, ensaios de dureza e ensaios de tração em corte com solicitação do lado do recuo. Os ensaios de tração foram realizados utilizando carregamentos monótonos, para as soldaduras nas duas condições de tratamento, e cíclicos, para as soldaduras não-tratadas termicamente. A análise metalográfica revelou a presença de defeitos do tipo Hook, no lado do avanço, e do tipo Cold Lap, no lado do recuo das soldaduras. Foram também observadas diferenças na morfologia do Nugget, para as soldaduras efetuadas com diferentes combinações de velocidades de rotação e de avanço. Apesar disso, quando solicitadas com cargas monótonas, as soldaduras não revelaram diferenças significativas de resistência, nas duas condições de tratamento. Observaram-se apenas diferenças apreciáveis, no modo de rotura em tração, para as soldaduras testadas após tratamento térmico de solubilização. A análise metalográfica revelou a ocorrência do fenómeno de crescimento de grão anormal (AGG), em toda a região do Nugget, durante o tratamento de solubilização. Observou-se uma correlação entre a heterogeneidade na morfologia e no tamanho do grão anormal no Nugget e o modo de rotura em tração. A microestrutura do Nugget terá tido também influencia na resistência à fadiga das soldaduras. As soldaduras efetuadas com maior passo (v/w), caracterizadas por menor tamanho de grão, revelaram resistência à fadiga superior à das soldaduras efetuadas com menor passo.

碩士
大同大學
材料工程學系(所)
101
This study deals with the blistering problem in die casting Al alloys when they are subjected to a T6 heat treatment. In order to realize the onset temperature and time conditions for the blistering problem to occur, two common die casting alloys, namely ADC3 (Al-9.2 Si-0.4 Mg-0.3 Fe) and ADC12 (Al-10.2 Si-1.6 Cu-0.9 Fe-0.3 Mg), were used and subjected to a series of solid solutioning tests. Once the blistering onset conditions were identified, proper T6 heat treatment can be applied to the alloys without the occurrence of blistering. Through a careful selection of heat treatment conditions (not to exceed the blistering onset conditions) and proper adjustments of alloy compositions (to lower the required solid solution temperature) die casting alloys can be strengthened by the blistering-free T6 heat treatment. The results show that the upper limits of temperature and time for the blistering-free solid solution treatment in ADC3 and ADC12 alloys are 480℃/0.25 h and 490℃/0.25 h, respectively. By correlating the high temperature strength data of ADC3 and ADC12 alloys to the onset temperature for blistering, it was found that the blistering occur when the high temperature strengths of the ADC3 and ADC12 alloys are equal to or less than 1.27 kgf/mm2 (or 12.4 MPa) and 1.14 kgf/mm2 (or 11.2 MPa), respectively. As such, blistering problems can be avoided by solid solutioning at a temperature below the onset temperature blistering, while the high temperature strengths of the alloys are strong enough to suppress the blistering from happening. The results also show that, when subjected to solid solutioning one hour at 460, 480, 490 and 520℃, the subsequent age hardening effect in the ADC3 alloy are respectively 10%, 39%, 72% and 100%. This means, under the blistering onset temperature of 490℃, the effect of solid solutioning decrease rapidly with a decrease in temperature. However, when Cu was added to the ADC3 alloy, the effect of solid solutioning is greatly enhanced in the same temperature range of 460 ~ 490℃. In the case of ADC3 + 2% Cu alloy, when subjected to solid solutioning one hour at 460, 480, 490 and 520℃, the subsequent age hardening effect in the alloy are respectively 66%, 82%, 83% and 100%. The comparison of age hardening effect in ADC3 and ADC3 + 2% alloys showed that the alloying of 2% Cu can greatly enhanced the hardening effect at the temperature range between 460 and 490℃. In the case of ADC12 alloy (containing 1.6% Cu) it was shown that, when subjected to solid solutioning one hour at 460, 480, 490 and 520℃, the subsequent age hardening effect in the alloy are respectively 83%, 91%, 99% and 100%. This means that in the ADC12 alloy a great amount of solid solutioning effect can be achieved even heat treated at a low temperature of 460℃(a temperature without blistering). It was also found in this study that the duration of solid solution treatment can be shortened from one hour to 0.25 hour without scarifying the subsequent age hardening effect. Comparisons of the mechanical properties of the above alloys in as-cast and un-blistering T6 heat treated (with solid solutioning treatment at 480℃ and 490℃ for 0.25 h) conditions show that both the tensile strengths and elongations increase by the T6 heat treatment. And the tensile strengths and elongations of the alloys solution treated at 490℃ are greater than those solution treated at 480℃.

碩士
崑山科技大學
機械工程研究所
106
It is well known that damage caused by the mechanical parts caused by wear and tear always seriously affect the accuracy of machinery. Hence, it is very important to improve the material properties of the mechanical elements. Anti-abrasion can improve the durability of machinery and equipment, thereby enhancing industrial competitiveness. Low friction can save energy. Therefore, it is important to establish the key technology of wear resistance and low friction for the related industries. Since aluminum alloys are commonly used on the conditions of fretting wear, however, the past researchs only have focused on steel materials. Therefore, it is necessary to improve the surface engineering of aluminum alloys before they are used. The effects of T6 heat treatment on fretting wear for the high silicon aluminum alloys were investigated in this study. These results have great practical importance for the precision machinery.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
O objetivo da dissertação de mestrado é estudar a influência de tratamentos térmicos nas propriedades mecânicas de soldaduras Cold Metal Transfer na liga de alumínio 6061-T6.Os quadros de bicicleta analisados, fornecidos pela empresa Triangle’s Cycling Equipment S.A, foram sujeitos a diferentes condições de tratamento. O tratamento térmico é constituído por solubilização, têmpera, seguido por um tempo de espera até se iniciar o envelhecimento artificial. Atualmente, as condições de tratamento utilizadas no fabrico dos quadros são 1h30 de solubilização a 535 ºC, seguido de um tempo de espera de 6h00 e envelhecimento artificial de 7h30 a 185 ºC.As principais variáveis estudadas foram o tempo de solubilização e o tempo de espera, sendo as temperaturas constantes. Foram estudados quadros sem tratamento: com um envelhecimento natural de dois meses após a soldadura e no estado como soldado. Além do estudo de um quadro conforme as condições de tratamento usadas pela empresa, também foram estudados quadros com outras condições de tratamento: com 1h30 de solubilização, seguido de um tempo de espera de 24h00 e envelhecimento artificial de 7h30; 0h45min de solubilização, seguido de um tempo de espera de 6h00 e envelhecimento artificial de 7h30.Por outro lado, pretendeu-se averiguar a hipótese de reduzir o tempo de tratamento de solubilização, por forma a otimizar o processo industrial da empresa, assim como analisar as consequências nas propriedades mecânicas resultantes de um tempo de espera de 24h00, provocadas por imprevistos no ciclo de produção.O quadro com as condições de tratamento utilizadas atualmente apresenta melhores propriedades mecânicas, tanto na análise de microdureza, como no comportamento à tração. Em comparação, o quadro com 0h45min de solubilização apresenta propriedades mecânicas relativamente inferiores. O quadro com 24h00 de espera também apresenta resultados relativamente inferiores, na análise de microdureza, mas resultados insatisfatórios no comportamento a tração.
The purpose of the master dissertation is to study the influence of thermal treatments on the mechanical properties of CMT welds in 6061-T6 aluminum alloy.The analyzed bicycle frames, supplied by Triangle's Cycling Equipment S.A, were subjected to different treatment conditions. The heat treatment consists of solubilization, quenching, followed by a waiting time until artificial aging begins. Currently the treatment conditions used in the manufacture of the frames are 1h30 of solubilization at 535ºC, followed by a waiting time of 6h00 and artificial aging of 7h30 at 180ºC.The main variables studied in this work were the solubilization time and the waiting time, with constant temperatures. Frames without treatment were studied, with a natural aging of two months after welding, and in the state as welded. Besides the study of frames matching the treatment conditions used by the company, there were also frames studied with other conditions of treatment: with 1h30 solubilization, followed by a waiting time of 24h00 and artificial aging of 7h30; 0h45min of solubilization, followed by a waiting time of 6h00 and artificial aging of 7h30.Alternatively, it was intended to investigate the hypothesis of reducing solubilization treatment time, in order to optimize the industrial process of the company, as well as to analyze the consequences on the mechanical properties resulting from a waiting time of 24h00, caused by unforeseen in the production cycle.The frame with the treatment conditions currently used has better mechanical properties, both in the microhardness analysis and in the tensile behavior. In comparison, the 0h45min solubilization frame has relatively lower mechanical properties. The frame with 24h00 wait also presents relatively lower results in the microhardness analysis, but poor results in the tensile behavior.