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Cooling rate effects on grain size, eutectic modification and Fe-bearing intermetallic precipitation in hypoeutectic Al-Si alloys

Ferdian, Deni. Cooling rate effects on grain size, eutectic modification and Fe-bearing intermetallic precipitation in hypoeutectic Al-Si alloys. PhD, Institut National Polytechnique de Toulouse, 2014

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Official URL: http://ethesis.inp-toulouse.fr/archive/00002786/

Abstract

Aluminum-silicon alloys are the most common aluminum casting alloys produced due to their fluidity characteristic and mechanical and light weight properties. However, there are several issues concerning application of Al-Si hypoeutectic alloys such as strength, which may be improved by refining grain size of the alloy and modifying silicon precipitates. Furthermore, precipitation of Fe-bearing intermetallics such as the so-called beta phase has a detrimental effect on tensile and ductility properties of Al-Si hypoeutectic alloys. Although various methods have been proposed to mitigate the effect of beta phase, the understanding of the mechanism of growth may be useful to reduce its detrimental effects. The objective of this study is to establish the relationship between the cooling rate and morphology features in Al-Si hypoeutectic alloys. In real casting condition, cooling rate is one of the factors that is not easy to predict, because it is related to the geometry of the parts and to the casting process itself. Changes in cooling rate affect the solidification process, and this is made apparent by the changes in the characteristic temperatures of cooling curves recorded in different locations of a part. The relation between these characteristic temperatures and grain size and eutectic silicon modification are presented. Furthermore, the present study also includes the effect of cooling rate on the morphology of beta phase in the case of a ternary Al-Fe-Si alloy. An attempt to characterize the growth of beta phase was performed through post-mortem and in-situ tomography. In addition, some variations from usual solidification features such as script monoclinic phase and rosettes were observed and are discussed.

Item Type:PhD Thesis
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Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
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Research Director:
Lacaze, Jacques
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Deposited On:18 Sep 2014 21:58

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