Effect of Magnesium Addition on the Cell Structure of Foams Produced From Re-melted Aluminum Alloy Scrap

Closed-cell foams were produced from re-melted aluminum alloy scrap that contained 0.13 wt pct Mg magnesium in the as-received state and higher levels after adding 1, 2, or 5 wt pct Mg. The excess Mg gave rise to the fragmentation of long oxide filaments present in the scrap alloy into smaller filaments and improved its distribution and wetting by the Al matrix. Foaming the re-melted scrap alloy containing 1, 2, and 5 wt pct Mg excess showed stability and good expansion in comparison to the scrap alloy containing 0.13 wt pct Mg only, but the cells became non-equiaxed when the Mg concentration was high (≥2 wt pct excess) due to cell wall rupture during solidification. Compressibility and energy absorption behavior were studied for scrap alloy foams containing 1 wt pct Mg excess, which is the optimum level to obtain good expansion, stability, and uniform cell size. Foams with densities in the range of 0.2 to 0.4 g cm−1 produced by holding at the foaming temperature for different times were used for the investigation. A uniform cell structure led to flatter stress plateaus, higher energy absorption efficiencies, and reduced “knockdown” in strength compared with commercial foams made by gas bubbling. The mechanical performance found is comparable to that of commercial foams made by a similar method but the expected costs are lower

Influence of particle additions on the foaming behaviour of AlSi11/TiH2 composites made by semi-solid processing

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Influence of alloying additions on foaming behaviour of thixocast AlSi11 precursor

Precursor for making aluminium foam via powder compact process was made by mixing metal and blowing agent powders, by compacting the mixture by cold isostatic pressing and by thixocasting the billet to a dense shaped product. The precursor was then foamed by heating to above the melting temperature of the alloy. We chose an AlSi11 alloy and 1 wt. of the common blowing agent titanium hydriide. In order to tailor foaming characteristics 1 wt. of one of the alloying elements Fe, Sn, Sb and In was added. The foaming behaviour was characterized with a mechanical expandometer. We showed that addition of Sn significantly increased maximum expansion, while Fe, Sb and In only had a minor influence. X ray radioscopic experiments confirmed this influence on maximum expansion due to the additives and showed that In and Sb containing foams are more stable than Sn for a longer time. This stability effect was also corroborated by the reduced coalescence rate and collapse degree measured for Sb and In. The findings are compared to the slightly different results found for AlSi6Cu4 in a previous study and are explained in terms of the changes in solidification range of these two alloys caused by the addition

Einsatz des Thixogießverfahrens zur Herstellung von Metallschaum aus AIMg4,5Mn0,7-Sägespänen

Zusammenfassend zeigen die durchgeführten Untersuchungen, dass sortenreine trockene Aluminiumspäne der Legierung EN-AW 5083 (AlMg(4.5)Mn(0.7)) für die Herstellung von aufschäumbarem Halbzeug mittels Thixogießen eingesetzt werden können. Obwohl Legierungen des Typs AlMg5 für ein vergleichsweise schlechtes Schäumverfahren bekannt sind, konnten durch Zugabe bestimmter Additive ausreichende Expansionen und Porenstrukturen eingestellt werden. Insbesondere bewährt hat sich die Zugabe von ca. 5 gew% Al2O3-Partikeln mit einer mittleren Partikelgröße von 3 Mym. Durch Verfahrensanpassungen beim Mischen der Späne und der pulverförmigen Zusätze konnte eine gute Homogenität und Reproduzierbarkeit des Schäumverhaltens erreicht werden. Die Wirksamkeit der zugegebenen Stabilisierungspartikel ist etwas geringer als bei Schäumen anderer Legierungen, eine Erklärung hierfür könnte in der Reaktivität des in der Legierung AlMg(4.5)Mn(0.7) enthaltenen Magnesiums liegen. Für weitere Verbesserungen bieten sich die Zugabe von Partikeln, die etwas weniger dem Angriff durch Magnesium unterliegen, aber auch die zusätzliche/alternative Zugabe geringer Gehalte an schaumstabilisierenden Legierungselementen an

Analysis of metal foaming behaviour and development of foaming processes

Metal foams were made by foaming precursors containing a blowing agent. Two different manufacturing routes for precursors were analyzed and compared hot pressing of powders and thixocasting of cold isostatically pressed powders. The foaming process was observed in situ by X ray imaging. Expansion kinetics, average pore sizes, drainage effects and pore morphologies were determined. The influence of gas atmosphere and overpressure on expansion and pore size was studied. Thixocasting parameters such as the pre heating conditions of the slug, the cold isostatic compaction pressure and TiH2 content were optimized. Foam expansion and drainage of the optimized precursor were studie

Investigation of the influence of stabilisation additions upon the structure and properties of foam produced by semi-solid processing

Using expandometry, X-ray computer-tomography in combination with a newly-developed software for pore-size evaluation and compression tests, the influence of adding elements and particles upon foaming behaviour, structure and mechanical properties of AlSi6Cu4 foams based on thixocast precursor materials was investigated. Especially for In and for 3micrometer-Al2O3-particles, significant improvements of the foaming behaviour as expressed by the maximum expansion levels obtainable could be observed. In contrast, no major variation of compression strength was substantiated by the experimental data, the exception to the rule being Sn additions, which led to a deterioration of strength as consequence of unfavourable microstructural characteristics. Pore sizes, however, have invariably been found to decrease irrespective of nature and concentration of additions. Thus the study suggests that the use of additives of the kind evaluated here should be motivated by requirements regarding expansion performance rather than maximum strength. However, given the limited number of samples available, the influence of the observed structural changes on the scatter of mechanical properties could not be judged. Therefore, a continuation of the present study to verify the influence of mesostructural features on property variation at given densities may be considered worthwhile