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Interprétation et traitement des données de sonde atomique tomographique : application à la precipitation dans les Al-Mg-Si

Abstract : The Al-Mg-Si-(Cu) alloys from the 6016 series are used in automobile industry as
closure panel sheets. They show a strong paint bake hardening behaviour (30 minutes
at 185°C, typically). This behaviour comes from structural hardening : the diffusion of
the solute elements in the supersaturated solid solution is activated by the heat treatment
and metastable phases precipitates form. These phases are coherent with the aluminium
matrix and slow the motion of the dislocations.
The dimensions of these metastable phases are sometimes below 1 nm and makes
them difficult to analyse otherwise than with a tomographic atom probe. New techniques
of data interpretation and processing have been developed in this field in order to push the
instrument beyond its limits.
With the help of the atom probe, sometimes associated with the transmission electron
microscope, the beta" precipitation mechanisms have been elucidated. In particular, we have
shown that a preageing treatment (90°C) makes the ageing treatment more efficient. This
is due to the formation of Mg- and Si-rich coherent clusters that increase the number
density of hardening objects (clusters + beta"). The presence of aluminium inside the b00
precipitates has been demonstrated.
The effect of the preageing treatment on the short range correlation between the solute
atoms during the very early stages of decomposition has been directly studied by
the use of partial pair correlation functions. By this method, we have also been able to
suggest a scheme for the natural ageing behaviour of the alloy : it could be explained by
the formation of solute atoms atmosphere in the vicinity of the dislocations. The interaction
between dislocations and atmospheres could be responsible for the natural ageing
hardening.
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Submitted on : Friday, June 2, 2006 - 1:33:12 AM
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  • HAL Id : tel-00077980, version 1

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Frederic de Geuser. Interprétation et traitement des données de sonde atomique tomographique : application à la precipitation dans les Al-Mg-Si. Matériaux. Université de Rouen, 2005. Français. ⟨tel-00077980⟩

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