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A necessidade de redução de custos de produção torna o caster mais vantajoso que o processo de placas, porém a aplicação dos produtos obtidos via vazamento contínuo é limitada pelas condições microestruturais. A alta taxa de resfriamento no processo de vazamento, que pode ultrapassar 300 °C/s, resulta em uma condição de supersaturação dos elementos em solução sólida. Quando as chapas são recozidas, ocorre precipitação na forma de dispersóides que atrasam a recristalização. Quando o material obtido via caster segue o processo convencional de placas laminadas a quente, com recozimento intermediário e têmpera obtida por reduções pré-definidas, o resultado é uma chapa com aspecto superficial e desempenho na estampagem prejudicados pela granulação grosseira. Para otimizar o processo é necessário aprimorar o conhecimento dos fenômenos de encruamento, recuperação, recristalização e crescimento de grãos além de relacioná-los aos processos industriais. A prática usual de processo para o material de caster consiste em um tratamento térmico de homogeneização para precipitar os elementos em solução sólida e melhorar a distribuição dos precipitados para que existam núcleos viáveis para a recristalização. O processo de homogeneização agrega um elevado custo na produção de chapas e pode ser substituído em determinadas aplicações por um tratamento de recristalização parcial que evita o crescimento de grãos. Para o presente trabalho, as amostras foram retiradas de rolos caster brutos de fusão e de placas laminadas a quente, nas ligas AA1200 e AA3003. As bobinas foram laminadas a frio até 0,88 mm e as amostras sofreram tratamentos térmicos em temperaturas entre 150 e 500 °C, com intervalos de 50 °C. O intervalo entre 200 e 450 °C foi melhor detalhado e os tratamentos térmicos foram feitos a cada 10 °C. Todos os tratamentos tiveram duração de 1 hora. Após tratamentos, foram feitas medidas de condutividade elétrica e dureza, ensaios de tração, Erichsen, análises químicas e caracterização microestrutural. O decréscimo das propriedades mecânicas em função do aumento da temperatura do tratamento térmico mostra o efeito da recuperação e recristalização nas amostras de chapas. A evolução das propriedades em função da temperatura é diferente quando se compara caster e placa, devido principalmente à taxa de resfriamento durante o vazamento do caster que mantém os elementos em solução sólida. A diferença é muito mais acentuada na liga AA3003, devido à baixa solubilidade sólida do manganês no alumínio, que precipita durante o tratamento térmico e atrasa a recristalização. Com a evolução das propriedades mecânicas em função da temperatura foi possível determinar a faixa ideal de tratamento térmico para a obtenção das têmperas objetivadas. / The necessity of reducing productions costs makes the continuous casting more advantageous than plates process, however, the application of the products obtained through continuous casting is limited by microstructural conditions. The high rate of cooling in the continuous casting, which can exceed 300 °C/s, results in a condition of supersaturation of the elements in solid solution. When the plates are annealed, precipitation occurs in the form of dispersoids that delays the recrystallization. When the continuous casting material follows the conventional process of hot-rolled plates, with intermediate annealing and hardness achieved by pre-defined reductions, the result is a plate with superficial appearance and performance in drawing hampered by the coarse graining. To optimize the process is necessary to improve the knowledge of the phenomena of cold working, recovery, recrystallization and grain growth in addition to relate them to industrial processes. The practice of process for continuous casting material consists in homogenization heat treatment to precipitate elements in solid solution and improve the distribution of precipitates in order to provide viable nuclei for the recrystallization. The process of homogenization adds a high cost in the production of plates and can be replaced in certain applications for treatment of partial recrystallization that prevents the grain growth. For this paper, the samples were taken from continuous casting rolls as cast and hot-rolled plates, in the alloys AA1200 and AA3003. The coils were cold-rolled up to 0.88 mm and the samples have undergone thermal treatment at temperatures between 150 and 500 °C, with intervals of 50 °C. The interval between 200 and 450 °C was better detailed and heat treatments were performed every 10 °C. All treatments had duration of 1 hour. After treatment, measures of electrical conductivity and hardness were made, besides traction tests, Erichsen, chemical analysis and microstructural characterization. The decrease of mechanical properties as a function of increasing heat treatment temperature shows the effect of recovery and recrystallization in samples of hot-rolled plates. The development of properties depending on the temperature is different when continuous casting and hot-rolled plates are compared, mainly due to the rate of cooling during the casting that keeps the elements in solid solution. The difference is more pronounced in the alloy AA3003, due to the low solid solubility of manganese in aluminum, which precipitates during the heat treatment and delays the recrystallization. With the evolution of mechanical properties according to the temperature, it was possible to determine the optimal range of heat treatment to obtain the desired hardness.

Wong Hoi Chun = Fe3O4和 ZnxFe3-xO4薄膜的制備及其熱處理效應 / 黃凱俊. / On t.p. "x" is subscript / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Wong Hoi Chun = Fe3O4 he ZnxFe3-xO4 bo mo de zhi bei ji qi re chu li xiao ying / Huang Kaijun. / Acknowledgement --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of contents --- p.iv / List of Figures --- p.vii / List of Tables --- p.xiii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction to magnetite and zinc ferrite / Chapter 1.1.1 --- Structure and properties --- p.1-1 / Chapter 1.1.2 --- Deposition methods of magnetite and zinc ferrite --- p.1-5 / Chapter 1.1.3 --- Review of Verwey transition --- p.1-7 / Chapter 1.1.4 --- Development of magnetic tunneling junction --- p.1-11 / Chapter 1.2 --- Research motivation --- p.1-13 / Chapter 1.3 --- Scope of this thesis --- p.1-14 / References --- p.1-15 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Thin film deposition / Chapter 2.1.1 --- Facing-target sputtering technique --- p.2-1 / Chapter 2.1.2 --- Vacuum system --- p.2-3 / Chapter 2.1.3 --- Asymmetric bipolar pulsed DC power source --- p.2-4 / Chapter 2.2 --- Annealing / Chapter 2.2.1 --- Vacuum annealing system --- p.2-8 / Chapter 2.2.2 --- Oxygen annealing system --- p.2-8 / Chapter 2.3 --- Characterization / Chapter 2.3.1 --- Profilometer --- p.2-10 / Chapter 2.3.2 --- X-ray diffractometer --- p.2-10 / Chapter 2.3.3 --- X-ray fluorescence spectrometer --- p.2-12 / Chapter 2.3.4 --- Rutherford backscattering spectrometer --- p.2-12 / Chapter 2.3.5 --- X-ray photoelectron spectroscopy --- p.2-13 / Chapter 2.3.6 --- Resistance measuring system --- p.2-15 / References --- p.2-17 / Chapter Chapter 3 --- Fabrication and characteristics of epitaxial Fe304 and ZnxFe3-xO4 single layer thin film / Chapter 3.1 --- Sample preparation / Chapter 3.1.1 --- Targets for reactive sputtering --- p.3-1 / Chapter 3.1.2 --- Substrates --- p.3-2 / Chapter 3.1.3 --- Deposition procedure --- p.3-4 / Chapter 3.2 --- Characterization of Fe3O4 thin films / Chapter 3.2.1 --- Effects of oxygen partial pressure --- p.3-5 / Chapter 3.2.2 --- Effects of substrate temperature --- p.3-10 / Chapter 3.2.3 --- Effects of deposition power --- p.3-17 / Chapter 3.2.4 --- Effects of deposition pressure --- p.3-19 / Chapter 3.2.5 --- Other factors --- p.3-19 / Chapter 3.3 --- Characterization of ZnxFe3-x04 thin films / Chapter 3.3.1 --- Effects of oxygen partial pressure --- p.3-22 / Chapter 3.3.2 --- Effects of substrate temperature --- p.3-28 / Chapter 3.3.3 --- Effects of thickness --- p.3-46 / Chapter 3.4 --- Fabrication and Characterization of ZnxFe3-x04 and Fe3O4 thin films on magnesium oxide(MgO) --- p.3-49 / References --- p.3-56 / Chapter Chapter 4 --- Annealing of epitaxial Fe304 and ZnxFe3-x04 thin films / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.2 --- Vacuum annealing of ZnxFe3-x04 thin film / Chapter 4.2.1 --- Enhancement in magnitude of the Verwey transition --- p.4-1 / Chapter 4.2.2 --- Reduction in resistivity --- p.4-5 / Chapter 4.2.3 --- Improvement of crystallinity --- p.4-5 / Chapter 4.2.4 --- Characterizations after high-temperature annealing --- p.4-11 / Chapter 4.2.5 --- Oxygen diffusion in atmosphere --- p.4-16 / Chapter 4.3 --- Oxygen annealing of ZnxFe3-x04 thin film --- p.4-18 / References --- p.4-22 / Chapter Chapter 5 --- Conclusions / Chapter 5.1 --- Conclusions --- p.5-1 / Chapter 5.2 --- Future outlook --- p.5-2