Castro Riglos, María Victoria (2011) Influencia de la deformación plástica y el microaleado sobre la precipitación en aleaciones de base Al-Cu. / Plastic deformation and microalloying effect on the precipitation of Al-Cu based alloys. Tesis Doctoral en Física, Universidad Nacional de Cuyo, Instituto Balseiro.
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Resumen en español
Debido a su gran abundancia en la naturaleza, a su bajo costo y su baja densidad el aluminio es un metal ampliamente utilizado tanto con fines tecnológicos y estructurales como también comerciales. Sin embargo, el Al no posee por sí mismo las condiciones necesarias de dureza para la mayoría de dichas aplicaciones. Por ello, en las últimas décadas se han desarrollado diversos métodos a través de los cuales la dureza se puede optimizar. Dos de ellos son el agregado de aleantes y microaleantes; y la aplicación de una deformación plástica previa a los tratamientos térmicos de envejecimiento. En el presente trabajo, el principal objetivo fue estudiar el efecto combinado de estos dos métodos en un sistema que ya ha sido ampliamente estudiado: Al-Cu. Los elementos microaleados fueron Si y Ge, en iguales proporciones (0,5 at. % de cada uno). Se estudió la evolución de la dureza y la micro estructura en Al-Cu microaleado con Si y Ge, con y sin deformación plástica previa al tratamiento térmico de envejecimiento. Se variaron el grado de deformación y la tem- peratura del tratamiento térmico de envejecimiento (160°C y 190°C). Con el objetivo de comprender mejor las observaciones hechas en Al- Cu-Si-Ge, se estudiaron también sistemas más simples (Al-Ge, Al-Si y Al- Si-Ge). La evolución de la dureza ante la deformación plástica previa se vinculó con la microestructura mediante la caracterización llevada a cabo por microscopía electrónica de transmisión. En este sentido, y con el fin de poder realizar mediciones cuantitativas de densidades de defectos, se implementó también un nuevo método para la determinación del espesor local de una lámina delgada. La deformación plástica previa al envejecimiento se aplicó tanto en compresión como en tracción, pero por cuestiones prácticas la mayor parte de los ensayos se llevó a cabo en compresión. La combinación de deformación plástica previa y el agregado de microaleantes resultó en una mejor respuesta de la dureza comparando con aplicar cada método por separado. Se estudió el efecto de aplicar distintos grados de deformación en los sistemas analizados. En este sentido, uno de los resultados más relevantes de este estudio mostró que existe un grado óptimo de deformación previa (cercano a1 8 %) para mejorar la dureza del Al-Cu-Si-Ge. Mediante la caracterización microestructural se determinó que la deformación plástica produce un aumento en la densidad de precipitados de Si-Ce que estimulan la nucleación heterogénea de la fase #theta#´, la cual es responsable por el mejor comportamiento de la dureza. Además esta precipitación de#theta# ´ fue más abundante y desarrollada. Se caracterizó el mecanismo de nucleación heterogénea de la fase l#theta#´•´ sobre precipitados de Si-Ce. Como una extensión de este trabajo, se comenzó a estudiar el agregado de los mismos microaleantes (Si y Ce) en el sistema Al-Cu-Mg, obteniéndose resultados muy promisorios con un importante incremento en los valores de dureza alcanzados respecto del sistema Al-Cu-Si-Ce. Esta mejora estuvo asociada nuevamente a la precipitación de la fase #theta#´ que es estimulada por precipitados muy pequeños de una fase precursora.
Resumen en inglés
Aluminium uses have been widely extended over technologic and commercial applications because of aluminium´s low weight and cost, and its high abundance in nature, though, aluminium by itself is not hard enough for many of these applications. For this reason, some methods have been developed in the last few decades, in order to improve hardness. Two of them are: alloying and microalloying other elements; and the application of plastic deformation prior to ageing heat treatments. The main goal of the present study was to analyze the combined effects of these two methods on a very well known system: Al-Cu. The chosen elements to be microalloyed were Si and Ge (0.5 at.% each). The hardness evolution and microstructure was studied in Al-Cu microalloyed with Si and Ge. Also plastic deformation prior to ageing heat treatments was applied under different degrees of deformation. Two temperatures for the ageing treatments were analyzed (160C y 190C). With the aim of a better understanding of the processes envolved, the related simpler systems have been also studied (Al-Ge, Al-Si, Al-Si-Ge). Hardness evolution response to predeformation was associated to microstructure by means of transmission electron microscopy (TEM). A new method for local thickness measurements was implemented. Plastic deformation essays were carried out in compression as well as in traction. For practical reasons, most of the times compression was the better choice. Plastic deformation combined with microalloys additions resulted in a better hardness response, than applying each method apart. Different deformation degrees prior to ageing have been applied. The results for Al-Cu-Si-Ge system, showed that an optimum deformation degree exists (around 8 %). Microstructural characterization determined that under plastic deformation prior to ageing, the rise produced in Si-Ge precipitates’s density stimulate #theta#´ phase heterogeneous nucleation that is responsable of the improvements on hardness behavior. This particular situation was linked to bigger and more abundant #theta#´ precipitates. The nucleation mechanism for heterogeneous nucleation of #theta#´ phase on Si-Ge precipitates was characterized. Finally, to widen the horizons, the effects of Si-Ge additions on Al-Cu- Mg have been explored. Promising results displayed an improved hardness behavior with respect to the one observed in Al-Cu-Si-Ge. Hardness improvements here were again related to an abundant #theta#´ precipitation. Although, in this case, the stimulating phase appeared to be an unidentified one that presented a big amount of very small precipitates spread all over.
| Tipo de objeto: | Tesis (Tesis Doctoral en Física) |
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| Palabras Clave: | Aluminium; Aluminio; Microstructure; Microestructura; Transmission electron microscopy; Microscopía electrónica por transmisión; Age hardenable alloys; Aleaciones termoenvejecibles; Microalloying; Microaleantes; Plastic deformation; Deformación plástica |
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| Materias: | Física > Física de materiales Metalurgia > Aleaciones |
| Divisiones: | Investigación y aplicaciones no nucleares > Física > Física de metales |
| Código ID: | 322 |
| Depositado Por: | Marisa G. Velazco Aldao |
| Depositado En: | 02 May 2012 13:25 |
| Última Modificación: | 02 May 2012 13:25 |
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