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Metal foam production from AlMg4.5Mn recycling machining chips by means of thixocasting and the effects of different additives for stabilization

Metallschaumherstellung mit recycleten Bearbeitungsspänen von AlMg4.5Mn mit dem Thixogießen und der Einfluss verschiedener Zusätze zur Stabilisierung
: Baumeister, J.; Weise, J.; Jeswein, A.; Busse, M.; Haesche, M.

Lefebvre, L.P.:
Porous metals and metallic foams, MetFoam 2007 : Proceedings of the Fifth International Conference on Porous Metals and Metallic Foams. September 5-7, 2007, Montreal, Canada
Lancaster, Pa.: DEStech Publications, 2008
ISBN: 978-1-932078-28-2
ISBN: 1-9320-7828-2
International Conference on Porous Metals and Metallic Foams (MetFoam) <5, 2007, Montreal>
Fraunhofer IFAM ()
AlMgMn-Legierung; Brikettieren; Calciumoxid; Metallschaum; Schaumbildung; Span; Stabilisierung; Thixocast-Verfahren

The use of recycled machining chips instead of aluminium powder to produce foamable precursor material leads to a significant decrease of the material and manufacturing costs. For the processing of aluminium cutting chips the thixocasting technique is appropriate because this technique offers the possibility to directly use chip-slugs briquetted analogueously to the normal procedure for chip recycling. The strong shearing of chip-material and the high temperatures during the thixocasting process lead to precursor components with a homogenous structure. For the present investigation the alloy AlMg4.5Mn0.7 was selected because large quantities of chips from this alloy are available resulting from e.g. sawing processes. The challenge was to improve the known unfavourable foaming characteristics of this alloy by the addition of small quantities of stabilizing particles, elements and their combinations. For the investigations the following additives were used: CaO, TiB2, Si3N4, Al2O3; Sn, Sb, as well as the combinations of CaO with Al2O3 and CaO with Sn. The foaming agent quantity was l wt.% TiH2 for all variants. The briquettes were heated in a conventional air-circulation furnace into the semi-solid state. After heating the slugs were transferred to the thixocasting machine and pressed into a plate cavity. For the qualitative evaluation of the foaming behaviour and the pore structure specimens of each mixture were foamed without and also within a foaming mould. The quantitative expansion and collapse behaviour of the samples were characterized with a mechanical expandometer. The different test methods showed the best foam stabilization characteristics for CaO, Si3N4 and Al2O3. Furthermore, it is interesting that the individual addition of CaO or Sn showed positive effects on the expansion, foam structure and the drainage. However, the combined addition of CaO and Sn led to good foam stabilization but also to some coarsening of the foam structure.
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