Abstract: Aluminium and Al-TiB2 closed-cell foams were produced by a recently developed foaming method called melt injection technique where bubbles are created by air entrainment. The macro- and microstructures of the foams were characterised by X-ray tomography and scanning electron microscopy, respectively. Mechanical properties were evaluated by quasi-static compression tests. Al-TiB2 foam exhibited finer cells and better mechanical properties compared to Al foam. Also, the structural and mechanical properties of these foams were compared with closed-cell foams produced by other existing methods. Graphic abstract: [Figure not available: see fulltext.]. © 2019, The Indian Institute of Metals - IIM.

Manas Mukherjee

Department of Metallurgical and Materials Engineering

Venkat Pamidi

Biswaranjan Muduli

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Transactions of the Indian Institute of Metals

A novel method to produce foams from metallic melts was invented. It is referred here as melt injection method. An apparatus to produce foams by melt injection method was also developed. In this method, bubbles are created through air entrainment by injecting a jet of molten metal into a pool of molten metal. These bubbles rise to the surface of melt pool and create a foam there. This method works without the need of an additional processing step to produce or add stabilising particles in the melt. In this study, foam from pure Al melt was produced with 93% porosity. X-ray tomography was used to visualise the macrostructure of the foams. Microstructural and phase analysis were carried out using SEM and XRD, respectively. These studies revealed the formation of alumina layer and particles at the gas-solid interface of cell walls. Stabilisation of foams produced by melt injection method was attributed to the combined action of oxide layer and particles. The mechanism of bubble formation through air entrainment was studied by using a water model set up. © 2018 Acta Materialia Inc.

Materialia

Melt injection – A novel method to produce metal foams

Foaming behavior of Al-Mg alloy melts with and without a thickening step was studied. Stable foams were obtained in both the cases. Oxides formed in Al-Mg melts were studied using XRD, SEM and TEM. These studies revealed the formation of MgAl2O4, MgO and transition oxides in Al-Mg melts. The stabilization of Al-Mg foams was attributed to the formation of MgAl2O4 and transition oxides. © 2017 Elsevier B.V.

Materials Letters

Foam stabilization by magnesium

In this study, the foaming behavior of metal matrix composites (MMCs) containing micron- and nano-sized TiB2 particles was compared. Foaming was achieved by adding blowing agent into the MMC melt at 670&nbsp;°C. Macrostructural and microstructural characterization of the foams were performed by using X-ray tomography and scanning electron microscopy. Quasi-static compression tests were conducted to analyze the mechanical behavior of the foams. Foams stabilized by nanoparticles showed higher expansion than those stabilized by micron-sized particles indicating a better stabilization by nanoparticles. The foams containing nanoparticles also exhibited better mechanical properties. This is mainly due to the presence of nanoparticles in the microstructure. © 2017 Elsevier B.V.

Materials Science and Engineering A

Influence of nano and micro particles on the expansion and mechanical properties of aluminum foams

Pressure-induced foaming (PIF) of metals is a foaming technique in which blowing agent free compacted metal powders are foamed. The method consists of heating hot-compacted metallic precursors to above their melting temperature under gas overpressure and foaming them by pressure release. This study focuses on PIF of Al99.7 and AlSi7 alloys under both air or Ar and overpressures up to 9&nbsp;bar. In situ x-ray radioscopy allows us to follow the foaming process and to perform quantitative analyses of expansion, foam morphology, and coalescence rate. Mass spectrometry helps to identify hydrogen as the foaming gas. Adsorbates on the former powder particles are found to be the primary gas source. Various advantages of this new method are identified and discussed. © 2015 The Minerals, Metals &amp; Materials Society.

Pressure-induced foaming of metals

We developed a novel process for foaming aluminum and its alloys without using a blowing agent. The process involves a designated apparatus in which molten aluminum and its alloys are first foamed under reduced pressure and then solidified quickly. Foaming was done for pure aluminum (99.99 pct) and AlMg5 alloy not containing stabilizing particles and AlMg5 and AlSi9Mg5 alloys containing 5 vol pct SiO2 particles. We discuss the foaming mechanism and develop a model for estimating the porosity that can be achieved in this process. The nucleation of pores in foams is also discussed. © 2012 The Minerals, Metals &amp; Materials Society and ASM International.

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