Berlin 2012 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 55: Topical Session Modern Atom Probe Tomography V - Steels, Alloys and Structural Materials

MM 55.4: Vortrag

Donnerstag, 29. März 2012, 16:30–16:45, H 0107

Atom probe tomography analysis of Sr-modified Al-Si hypoeutectic alloy — •Jenifer Barrirero, Michael Engstler, Hisham Aboulfadl, and Frank Mücklich — Functional Materials, Department of Materials Science, Saarland University, D-66123 Saarbrücken, Germany

Al-Si casting alloys are of great industrial importance. The addition of traces of Sr, causes a flake-to-fibrous transition which contributes to the improvement of tensile, impact and thermal shock properties. In order to obtain a better understanding of the underlying mechanisms occurring during this modification, an analysis of Sr distribution was done by laser pulsed atom probe tomography. Site-specific sample preparation of unmodified and modified (150 ppm Sr) hypoeutectic AlSi7 alloy was accomplished by focused ion beam methods. The concentration of Sr at the eutectic Al-Si boundary and its distribution in the eutectic Si were analysed. The results revealed nanometric segregations in the eutectic Si with two to three times more Al than Sr. These features showed linear and planar morphologies which are, to some extent, in agreement with the fundamentals of the impurity induced twinning theory for modification. A morphological comparison between the eutectic Al-Si boundary of modified and unmodified alloys showed a change in the growth front of the eutectic phase as proposed by early theories. The unmodified alloy presented an inhomogeneous jagged boundary in accordance with an endogenous type of growth, while modified specimens had a smoother boundary morphology possibly related to a retarded growth rate of Si.