Al Foam Research Articles

Characterisation and Mechanical Testing of Open Cell Al Foams Manufactured by Molten Metal Infiltration of Porous Salt Bead Preforms: Effect of Bead Size

Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of molten Al occurred into beads of all sizes and was predicted using a simple model. The yield strength of the porous structures increased with increasing density and decreasing pore (bead) size. Despite the non-optimum distribution of metal in the porous structure, due to partial infiltration within the beads, the magnitude and density dependence of the yield stress were comparable with those for pure Al foams reported in similar studies. The structural efficiency was improved for structures produced at lower infiltration pressure, where the metal is predominantly distributed in the cell walls. The rate of salt dissolution from the preforms was high, in particular for high density preforms, large beads and preforms infiltrated at low pressures, owing to the ability of the porous beads to collapse as well as dissolve.

An appraisal of the heat transfer properties of metallic open-cell foams for strongly exo-/endo-thermic catalytic processes in tubular reactors

We assess the heat transfer properties of open-cell foams, i.e. cellular materials made of interconnected struts, in view of their use as catalyst carriers. Metallic foams made of FeCrAlY and aluminum with 89–95% porosities and 10–40PPI (pores per linear in.) pore densities were investigated. Geometrical measurements of all samples were performed using optical microscopy. X-ray micro-computed tomography techniques were applied for a detailed morphological characterization of selected samples. Heat transfer data were collected in heating and cooling flow experiments, under operating conditions expected to involve conductive as well as both convective and radiative heat exchange, using N2 flow rates from 15 to 35Nlmin−1 in the 400–800K T-range. The effective radial and axial conductivities and the wall heat transfer coefficient were estimated from the measured steady-state temperature profiles. The estimates of the effective radial conductivity were between 0.3Wm−1K−1 and 0.9Wm−1K−1 for FeCrAlY samples with ∼95% porosity, while they increased up to 7.7Wm−1K−1 for aluminum samples with ∼89% porosity. The latter value is comparable with or higher than typical effective radial thermal conductivities in technical packed bed reactors. The role of heat conduction in the foam solid matrix was also analyzed by solving the Laplace heat diffusion equation in a 3D mesh of foam samples virtually reconstructed by micro-computed tomography. It was found that the conductive mechanism is the dominant contribution to the effective radial conductivity for both FeCrAlY and Al foams. In the case of highly conductive materials, such as Al, the convective and radiative contributions are essentially negligible, and the wall coefficient (hw) becomes the controlling heat transfer parameter. The estimates of the wall heat transfer coefficient exhibit an inverse dependency on the foam cell size, but are unaffected by changes in the porosity and in the fabrication material of the foams.

Removal of bacterial pathogen from wastewater using Al filter with Ag-containing nanocomposite film by in situ dispersion involving polyol process

In this study, a filter with deposited Ag/Al(OH)3 mesoporous nanocomposite film was fabricated to remove bacterial pathogens from wastewater. Mesoporous Al(OH)3 film was generated on the Al foam body by alkali surface modification, followed by immersion in a polyol solution for 4h at an elevated temperature in order to deposit silver nanoparticles (Ag NPs). The Al(OH)3 porous matrix showed a significant increase in specific surface area due to the large size of the voids between flakes, which reached several tens of nanometers. After in situ three-dimensional deposition of Ag NPs by a polyol process, the Ag NPs were nucleated and grown at the surface of the mesoporous Al(OH)3 film. The filter with Ag/Al(OH)3 mesoporous nanocomposite film showed a good bacterial pathogen removal rate within a very short contact time compared to the untreated Al foam filter. Filters with deposited Ag/Al(OH)3 mesoporous nanocomposite film have great potential for application as antimicrobial filters for tap water purification, wastewater treatment, and other bio-related applications.

Effects of scandium additions on mechanical properties of cellular Al-based foams

By using titanium hydride as the blowing agent and Ca particles as the thickening agent, the cellular Al-0.24wt.%Sc and Al-0.41wt.%Sc foams with a porosity ranging from 48 to 86% were successfully fabricated via the melt-foaming method. The compressive behaviors and effects of minor Sc additions on the strengthening mechanism of the cellular Al–Sc alloy foams were investigated and discussed. The results show that minor Sc additions can dramatically improve the compressive strength of the cellular Al foams due to the grain refinement and pinning effect from the Al3Sc precipitates homogeneously distributed in the matrix after heat treatment, implying that the Sc addition coupled with proper heat treatment is an effective way to improve the mechanical performance for Al-based alloy foams.

Effect of processing parameters and glycerin addition on the properties of Al foams

Aluminum foam has been produced by sintering and dissolution processes using NaCl powders as a space holder. In this research, glycerin is used as a novel lubricant along with acetone. The effects of the processing parameters including compacting pressure, sintering temperatures (620, 640 and 650 °C), size, and volume fraction of the space holder, on the physical and mechanical properties of the produced foams have been investigated. Due to segregation of the Al and NaCl powders at high compaction pressures, spalling of Al foams was observed. Meanwhile, adding small amounts of acetone and glycerin to the mixture ensures homogeneity and prevents segregation of dissimilar powders at varying pressure. Moreover, the addition of glycerin provides an improved homogenous stress distribution within the produced foams during mechanical testing, which in turn halts crack propagation. Meanwhile, an alternative technique to remove NaCl particles during the dissolution stage has been proposed. The results showed that high quality foams were successfully produced under a compaction pressure range of 250–265 MPa and sintering temperature of 650 °C.

Friction Powder Compaction for Fabrication of Open-Cell Aluminum Foam by the Sintering and Dissolution Process Route

A new friction powder compaction (FPC) process by the sintering and dissolution process (SDP) route for fabricating open-cell aluminum (Al) foam, which requires no external heat sources, was developed. Foams with porosities of 74 and 83 pct were successfully fabricated and their compressive responses were investigated. The sintered mixture during the removal process was observed nondestructively by X-ray computed tomography (CT) to reveal the progress of the removal of soluble particles and to confirm that they were completely dissolved.

307 発泡アルミニウムの型充填における金型回転の効果

In order to improve mould filling of aluminium foams into mould cavity, a moulding process of foams is proposed. In the experiment of moulding of Al foams, a precursor made by hot powder extrusion is put into the die for foaming of alulminum and extruded into a rotating mould during foaming at 750 ℃. In case of large inlet diameter of mould, the influence of gravity is significant. When the mould of large diameter is rotated and filled with Al foam, the mould filling ratio is improved.

A comparative study of replicated pure Al and AC3A composite foams

Pure Al and AC3A Al alloy, mixed with SiC particles, have been used to produce open-cell composite foams through replication process of polyurethane foam preform, assisted with infiltration pressure. The addition of SiC particles is between 1 – 5wt.%. A comparative examination of cellular microstructure and compressive strength of both foams is undertaken. It is demonstrated that although both have similar foam structure and particle content, but the disparities in matrix microstructure and properties result in distinct mechanical properties.

Vacuum Foaming of Aluminum Scrap

ABSTRACTIn this study, scrap from the automotive industry was used to produce aluminium foams under vacuum. Chips of an aluminium alloy LM26 were melted and 1wt. % of Mg was added for creating a viscous casting with uniform distribution of oxides. An ingot was obtained of this alloy after casting and solidification. Trials for foaming this alloy were performed by re-melting pieces under vacuum at different temperatures. A window in the vacuum chamber allowed observation of the foaming and collapse of the porous structures was observed during cooling. Characterization of the aluminum foams revealed different levels of expansion, porous structures and degrees of drainage. The best foams were obtained at 680 °C with a density of 0.78 g/cm3. This technique appears to be a feasible low cost route for producing Al foams based on scrap material.

Mechanical Properties and Energy Absorption Capability of Closed-Cell Al Alloy Foam

Based on compression tests of closed-cell Al alloy foam measured, mchanical properties and energy absorption capability had been investigated. The compressive stress-strain curve of closed-cell Al foam consists of three distinct regions, i.e., the linear elasticity region, the plastic collapse region or brittle crushing region, and the densification region. Formula on energy absorption capability of closed-cell Al alloy foam was presented, which could provide theoretical support for its engineering application.

The effect of oxides in various aluminium powders on foamability

Al powders, manufactured by different powder metallurgical methods, with various sizes have been used to produce Al foams. Different oxide contents in various Al powders play a major role in foam expansion and stability. The airatomised coarse Al powder with a high oxide content of 0.536wt.% shows the largest foam expansion. Of similar particle size, a small foam expansion is found when the centrifugally atomised coarse Al powder with 0.061wt.% oxide is applied. The large foam expansion resulted from a high content of oxide clusters of crumpled films developed during foaming process.

Mechanical Properties and Energy Absorption Capability of Closed-Cell Al Alloy Foam

Based on compression tests of closed-cell Al alloy foam measured, mchanical properties and energy absorption capability had been investigated. The compressive stress-strain curve of closed-cell Al foam consists of three distinct regions, i.e., the linear elasticity region, the plastic collapse region or brittle crushing region, and the densification region. Formula on energy absorption capability of closed-cell Al alloy foam was presented, which could provide theoretical support for its engineering application.

The Indentation Behavior of Closed-Cell Al Foam under the Flat-End Cylindrical Indenter

The indentation response of the closed-cell Al foam under the flat-end cylindrical indenter is examined by use the finite element method. The MSC/Marc finite element package is used to model the indentation response of the foam panels, and the Al foam was defined in MSC/Marc as the homogeneous, elasto-plastic material. The simulation result reveals that the deformation was found to be almost totally restricted to a spherical cap-shape compacted zone under the indenter, and the shape of the deformation zone is similar to the observed phenomenon from the indentation test.

Preparation of Al Foam Sandwiches and Analyzing on the Interface Solidification Microstructure

Al Foam Sandwiches (AFS) has been created by a process of hot pressing Al-TiH2 precursor (core) made by cold pressing together with steel sheet, and then foaming. The microstructure and composition of Al-Fe interface has been analyzed by SEM and Element Linescanning Electron Microscopy (ELEM). The experiment and analysis show that during hot pressing process, firm mechanical bonding is formed between steel sheet and core, during foaming, the intermetallic compound FeAl3 and eutectic structure (FeAl3+Al) were formed by diffuse of Fe and Al elements each other at the interface, which gave a rise to a good metallurgical bonding interface between sheet and core.

The Manufacture and Characterisation of Aluminium Foams Made by Investment Casting Using Dissolvable Spherical Sodium Chloride Bead Preforms

Open cell Al foams have been made by infiltrating molten Al into preforms made from porous salt spheres. Infiltration has been effected using simple pressure-assisted vacuum investment casting where the maximum infiltration pressure difference was less than 36 psi. The preform and resulting foam density decreased with increasing compaction pressure and the foam density increased with increasing infiltration pressure. For low pressure infiltration, and high density preforms, salt dissolution was rapid due to the porous nature of the salt spheres. Infiltration of molten Al occurred into the beads and, for high density preforms and higher infiltration pressures, the volume of metal in the beads exceeded that in the cell walls, drastically decreasing the NaCl dissolution rate. A simple approach is shown whereby the data from mercury porosimetry can be used to predict the resulting foam density, thereby aiding the design of preform and beads structures.

Effect of Sn on the Dehydrogenation Process of TiH2 in Al Foams

The study of the dehydrogenation process of TiH2 in aluminum foams produced by the powder metallurgy technique is essential to understanding its foaming behavior. Tin was added to the Al foam to modify the dehydrogenation process and stabilize the foam. A gradual decomposition and more retention of hydrogen gas can be achieved with Sn addition resulting in a gradual and larger expansion of the foam.

Fabrication and Mechanical Testing of the Aluminum Foam Produced by Sintering and Dissolution Process

In the present study, fabrication of the aluminum (Al) foam through sintering and dissolution process and effect of space holder (NaCl) mean size on compressive behavior of metallic foam has been investigated. Due to improper cold bonding between Al particles in low compaction pressure spalling of the foam was observed. Appropriate compacting pressure and sintering temperature of the compacts resulted in production of high quality Al foams. SEM was used to characterize the morphology of produced Al foam and mechanical behavior of produced foams was evaluated using compression test machine. The results show that open-cell Al foam free from cracks was obtained and an increase in NaCl mean size resulted in increases of the compressive strength, Young modulus and plateau stress of the stress-strain curves.

Mechanical and energy absorption behaviors of metal/polymer layered sandwich structures

This article considers the sandwich structures with aluminium (Al) foams of various thicknesses in conjunction with skins composed of fibre-metal laminates (FML). The FMLs with Al sheet and glass fiber reinforced polypropylene (GFPP) composites were integrated with Al foam for composing the sandwich panels. The FML–foam sandwich systems were manufactured by hot pressing in a mold at 200°C under 1.5 MPa pressure. The bonding between the components of the sandwich was achieved by various surface modification techniques, i.e., silane surface treatment, PP adhesive film additition, and their combination. The Al sheet/Al foam sandwiches were also prepared by bonding the components with an epoxy adhesive for comparing the effect of GFPP on the mechanical performance of the sandwich structures. The energy absorption capacities together with compressive mechanical behavior of both Al foams and FML-foam sandwich systems were evaluated by flatwise compression tests. Experiments were performed on samples of varying foam thicknesses.

Synthesis of carbon nanotubes by fine Ni particles in Ni3Al foam

Abstract The reaction of Ni and Al particles may induce the formation of nickel aluminide intermetallics. However, the imcomplete reaction can produce very fine Ni particles, which are dispersed in a porous Ni3Al skeleton. The composite foam structure can then be used in the synthesis of carbon nanotubes (CNTs) at high temperatures. In this work, the process for this new structure, and then for synthesizing CNTs was investigated. Firstly, fine Ni particles in an Ni3Al porous structure formed by incomplete reaction between Ni and Al powder were made. Then, the effect of the addition of foaming agent, NaCl, on the porosity of the porous structure was studied. This showed that the porosity increases sharply with the addition of NaCl, and a porosity as high as 90% was obtained. Multi-walled CNTs were found in the products of catalytic decomposition of methanol by fine Ni particles in the composite foam structure. Finally, the potential applications of this composite foam structure in the low-cost manufacturing of CNTs, micro-channeled reactors and in-situ CNT reinforced composites are discussed.

Fabricating Al Foam from Turning Scraps

This article describes the sintering-dissolution process (SDP) that is employed for fabricating aluminium foams from AA336 turning scraps. The effect of sintering temperature, chip size, and chip weight fraction in the NaCl/Al mixture on the mechanical properties of the foams produced was also investigated. The results indicate that, in contrast to commercial-purity Al foams, which (as stated in the literature) can be produced in SDP by either liquid- or solid-state sintering, solid-state sintering does not take place between the AA336 chips, and so melting of the chips is essential to form a strong network structure in the preform. A chip weight fraction of 60%, chip size of about 0.5 mm, and a sintering temperature of 600°C were determined to be the optimum parameters for a successful sintering dissolution process for the fabrication of Al foams from AA336 turning scraps.