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Title: Grain refinement in a AlZnMgCuTi alloy by intensive melt shearing: A multi-step nucleation mechanism
Authors: Li, HT
Xia, M
Jarry, P
Scamans, GM
Fan, Z
Keywords: Grain refinement;Nucleation;Solidification;Alloys
Issue Date: 2011
Publisher: Elsevier
Citation: Journal of Crystal Growth, 314(1): 285-292, Jan 2011
Abstract: Direct chill (DC) cast ingots of wrought Al alloys conventionally require the deliberate addition of a grain refiner to provide a uniform as-cast microstructure for the optimisation of both mechanical properties and processability. Grain refiner additions have been in widespread industrial use for more than half a century. Intensive melt shearing can provide grain refinement without the need for a specific grain refiner addition for both magnesium and aluminium based alloys. In this paper we present experimental evidence of the grain refinement in an experimental wrought aluminium alloy achieved by intensive melt shearing in the liquid state prior to solidification. The mechanisms for high shear induced grain refinement are correlated with the evolution of oxides in alloys. The oxides present in liquid aluminium alloys, normally as oxide films and clusters, can be effectively dispersed by intensive shearing and then provide effective sites for the heterogeneous nucleation of Al3Ti phase. As a result, Al3Ti particles with a narrow size distribution and hence improved efficiency as active nucleation sites of alpha-aluminium grains are responsible for the achieved significant grain refinement. This is termed a multi-step nucleation mechanism.
Description: This is a post-print version of the article. Copyright @ 2010 Elsevier B.V.
ISSN: 0022-0248
Appears in Collections:Brunel Centre for Advanced Solidification Technology (BCAST)

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