Aluminum Foam Samples Research Articles

Production of aluminum foam using an alternative porophore

Subject of research: blowing agent in the form of natural CaCO3 powder to obtain high-quality aluminum foam material. Purpose of research: selection of the optimal type of foam as a pore-forming element and production of aluminum foam with special functional properties. Methods and objects of research: when studying the gas-forming properties, the residual substances and thermal stability of the powder were determined using a thermogravimetric analyzer TG-DTG, DSC. The processes of obtaining aluminum foam samples sintered in a protective environment on an experimental installation are considered. The object of research is the resulting CaCO3 powders, as well as the determination of the physical and mechanical properties of aluminum foam samples. Main results of research: production of foamed aluminum with special functional properties with the introduction of powder blowing agent CaCO3. Selection of the optimal component of the amount of powder injected into the metal matrix of the substance, based on the physical properties of the resulting material.

Numerical Simulation of Aluminum Foams by Space Holder Infiltration

AbstractThis study explores the simulation and analysis of the infiltration process for manufacturing A356 aluminum alloy foams using vacuum pressure. The infiltration technique, known for its versatility in liquid-state metal processing, is widely employed for metal foam production due to its ease of application. The study investigates the relationship between the geometric parameters of the preform, system pressure, and filling times, revealing a correlation. The simulation using the Flow 3D software determines the pressure and vacuum time required to achieve successful aluminum foam without filling failures. Experimental validation through infiltration casting using NaCl as a removable preform aligns with the simulated results, yielding high-quality aluminum foam samples with diverse pore sizes (0.5 mm, 1.0 mm, and 2.0 mm), uniform and interconnected pore distribution, average porosity percentages of 65%, and a relative density of 0.35. The research contributes insights into optimizing the infiltration process for aluminum foam fabrication, bridging the gap in limited literature on cellular metals.

Refoaming of deformed aluminum foam fabricated by precursor foaming process using remaining foaming agent and densification using friction stir welding

Once aluminum foam is damaged and deformed, its pores collapse and cannot be restored. In this study, refoaming of compression-deformed aluminum foam was attempted. It was found that deformed aluminum foam can be refoamed by densification treatment using friction stir welding (FSW), followed by heat treatment for foaming. In contrast, when refoaming was carried out without FSW after compression, little foaming was observed. The porosity of samples refoamed by applying FSW was similar to that of the aluminum foam samples before compression. In contrast, samples refoamed without applying FSW exhibited low porosities. From XRD analysis, it was shown that foaming agent remained undecomposed during the foaming which can be used for refoaming.

Study on Sound Absorption Performance of Aluminum Foam Combination

Aluminum foam is a kind of new material with a large number of holes distributed in aluminum alloy. It has the characteristics of lightweight, sound absorption, energy absorption and vibration reduction, and other porous materials. Aluminum foam has good acoustic performance. However, its excellent sound absorption ability is only reflected in the middle and high-frequency bands. Besides, the low-frequency sound absorption ability is very poor and the frequency band is narrow. Therefore, in this paper, different types of perforated aluminum foams with different parameters are combined to explore the influence on acoustic performance and find that the combination of large porosity perforated sample and aluminum foam has a better sound absorption effect. The unperforated sample is placed in front of the perforated sample to improve the sound absorption coefficient of the low and medium frequencies. Finally, different types of perforated aluminum foam samples were properly combined, and it was found through the test that almost all sound waves in the band of 1200 HZ~2000 Hz could be absorbed by the combined structure.

Mapping 3D grain and precipitate structure during in situ mechanical testing of open-cell metal foam using micro-computed tomography and high-energy X-ray diffraction microscopy

• 3D grain structure is mapped and tracked during loading of open-cell metal foam. • Challenges included sample size relative to beam size and large ligament motions. • X-ray CT and far-field HEDM measurements collected at incremental displacements. • New scanning and stitching methodology established for far-field HEDM measurements. • Ligament-tracking code used to express crystal orientation in local reference frame. Open-cell metal foams are ultra-low-density cellular metals with complex hierarchical structures that span bulk, cell, ligament, and sub-ligament scales and give rise to desirable properties such as high strength-to-weight ratio and excellent energy absorption. Although literature suggests that intrinsic material structures at sub-ligament length scales (e.g., grains and precipitates) play an important role in mechanical behavior of open-cell metal foams, there are very few experimental measurements of such structures in three dimensions and for meaningful volumes of foam. This study seeks to map and track the three-dimensional (3D) grain and precipitate structures of an intact volume of open-cell aluminum foam by advancing microstructural characterization techniques that leverage X-ray micro-computed tomography ( μ CT ) and far-field high-energy X-ray diffraction microscopy (FF-HEDM). A 6%-relative-density aluminum foam sample was mechanically tested in compression while μ CT and FF-HEDM measurements were collected at interrupted loading states at beamline 1-ID of the Advanced Photon Source. A new scanning strategy and reconstruction algorithm were established to enable characterization of a foam volume with diameter approximately four times wider than the nominal width of the X-ray beam. The result is a set of maps that detail both the 3D grain and precipitate structures throughout the foam volume at successive strain steps. A novel grain tracking procedure was developed to track individual grains within the foam volume by accounting for the large rigid-body motions that individual ligaments can undergo during mechanical loading. The ability to track grains and precipitate structures in three dimensions throughout large bulk deformation of ultra-low-density polycrystalline materials enables new possibilities for validating numerical models and investigating local failure mechanisms. Furthermore, the methods and procedures developed in this study could be applied to other ultra-low-density structures, such as additively manufactured lattices.

Effect of sample shape on compression behavior of aluminum foams

The paper deals with the effect of the sample shape on the uniaxial compression behavior of powder metallurgically prepared closed cell aluminum foams with surface skin. The combination of various geometry shapes of aluminum foams is important in the case of design and development of optimal seismic and impact energy absorbers. Aluminum foam samples of the same density were prepared by a powder-metallurgical process from two different aluminum foam alloys: ductile AlMg1Si0.6 + 1 % wt. TiH2 and brittle AlSi10 + 1 % wt. TiH2. The samples were foamed in three different geometric shapes (cylinder, triangular prism and square prism) with the same cross-sectional area of 490 mm2. The samples contain surface skin. Quasi static uniaxial compression tests were performed parallel to the remaining outer surface skin on the foams with the constant density. From the obtained stress–strain curves compression strength, plateau strength, energy absorption at 50 % strain and densification strain were determined. The results indicate that there is an effect of sample shape on the aluminum foam mechanical properties: triangular prism mechanical properties are the worst with respect to cylinders and square prisms. The results indicate that the square prism compression properties could outperform compression properties values of cylinders for both ductile and brittle aluminum matrix alloy. Densification strain is shape independent. The observed results were explained by foam inhomogeneity, size of pores, thickness of surface skin region and stiff edges of used shapes.

Investigation of the Relationship between Morphology and Thermal Conductivity of Powder Metallurgically Prepared Aluminium Foams.

Among different promising solutions, coupling closed-cell aluminium foam composite panels prepared by a powder metallurgical method with pore walls interconnected by microcracks, with low thermal conductivity phase change materials (PCMs), is one of the effective ways of increasing thermal conductivity for better performance of thermal storage systems in buildings. The internal structure of the foam formation, related to the porosity which decides the heat transfer rate, plays a significant role in the thermal energy storage performance. The dependence of the heat transfer characteristics on the internal foam structure is studied numerically in this work. The foamable precursor of 99.7% pure aluminium powder mixed with 0.15 wt.% of foaming agent, TiH2 powder, was prepared by compacting, and extruded to a volume of 20 × 40 × 5 mm. Two aluminium foam samples of 40 × 40 × 5 mm were examined with apparent densities of 0.7415 g/cm3 and 1.62375 g/cm3. The internal porous structure of the aluminium foam samples was modelled using X-ray tomography slices through image processing techniques for finite element analysis. The obtained numerical results for the heat transfer rate and effective thermal conductivity of the developed surrogate models revealed the influence of porosity, struts, and the presence of pore walls in determining the heat flow in the internal structure of the foam. Additionally, it was found that the pore size and its distribution determine the uniform heat flow rate in the entire foamed structure. The numerical data were then validated against the analytical predictions of thermal conductivity based on various correlations. It has been found that the simplified models of Bruggemann and Russell and the parallel–series model can predict the excellent effective thermal conductivity results of the foam throughout the porosity range. The optimal internal foam structure was studied to explore the possibilities of using aluminium foam for PCM-based thermal storage applications.

Thermal management of power electronics with liquid cooled metal foam heat sink

In this paper, a combined experimental and numerical study of liquid cooled aluminum foam (AF) heat sink applicable for high power electronics cooling was conducted. AF heat sinks with porosity (0.88) and pore densities (10 PPI and 20 PPI) are fabricated and the empty channel is employed for comparison. Experimental measurements were conducted subjected to non-Darcy flow regime. Numerical analysis was based on the Brinkman-Forchheimer extended Darcy momentum model, together with the energy equations of local thermal non-equilibrium (LTNE) and local thermal equilibrium (LTE) models. The permeability and inertia coefficient of the AF samples were correlated based on the measured pressure drop. New correlations of interfacial heat transfer coefficient between water and AF solid matrix were also determined. Numerically predicted local surface temperature and temperature field distributions were presented and validated with the experimental measurements. The results reveal that the permeability decreases and the inertial coefficient increases with increasing pore density. The thermal performance of AF heat sinks is appreciably superior to the empty channel, under a given flow rate, the Num of the AF heat sink can be 1.40–1.76 times of the empty channel. Heat transfer enhancement by 20 PPI foam is inappreciable, approximately 5%, compared to that of 10 PPI. The LTNE model demonstrates more accurate for predicting the spatial temperature distributions than the LTE model. The results also indicate that the non-equilibrium heat transfer phenomenon in water-cooled AF heat sink is not pronounced, and the non-equilibrium effect is declined with increasing velocity.

Performance and heat transfer measurements in asymmetrically-heated metal foam cooled by water

Metal foams are attractive for heat transfer applications because of their large surface area to volume ratio, and their complex structure that promotes mixing and convection. Usually metal-foam applications involve symmetric heating. The literature shows that thermal asymmetry imposed on the boundaries substantially affects the heat transfer in porous media, including metal foam. It also shows that most, if not all, the published information in this regard is numerical and/or analytical and for fully-developed flow and heat transfer conditions. Typically, the Darcy flow model is employed. There seems to be lack of experimental data, especially in the more practical non-Darcy flow regimes. In this study, a metal-foam-filled rectangular channel subjected to constant heat flux of 12,787 W/m2 on one side was used to investigate convective heat transfer. The open-cell aluminum foam sample had 20 pores per inch and 91.8% porosity. The experimental work was conducted in the Reynolds number range 2.8–25 using water as a working fluid. Pressure drop measurements showed that the flow was in the Forchheimer regime. The permeability was obtained as 3.88 × 10−8 m2 and the Forchheimer coefficient was 0.085. The Fanning friction factor correlated with the permeability-based Reynolds number to the power − 0.5. The thermal entry length was determined for the lower flow velocities and reached 2.6 hydraulic diameters. Heat transfer results showed that the average Nusselt number correlated well the Reynolds number in a power law with the exponent of Reynolds number being 0.61. The Nusselt number reached a plateau at around Reynolds number equals 10. The Colburn j factor for the metal-foam heat sink correlated with the Reynolds number to the power −0.39, and was 407% higher than that of an empty channel. A way of isolating the effect of the random orientation of the ligaments of the foam was devised by comparing the performance of the foam to staggered pin fins having the same porosity and a diameter equal to the ligament of the foam. The orientation of the ligaments of the foam was responsible for about 33% average increase in heat transfer. The experimental data and correlation of obtained can aid numerical and modeling work concerning asymmetrically-heated metal-foam heat transfer.

Study on Cell Deformation of Low Porosity Aluminum Foams under Quasi‐Static Compression by X‐Ray Tomography

Understanding the correlation between cell deformation and initial cell structure during compression is important for improvement and development of effective applications of aluminum foams. Foams with porosities lower than 75% now get more attention because of more spherical cells and better mechanical performance. Herein, two low porosity aluminum foam samples are deformed by a compressive device allowing simultaneous X‐ray tomography. The foam cell structures in the initial undeformed state and in the state, where the first batch of cells deforms, are characterized and correlated. The absolute value of anisotropy change is selected as the most sensitive parameter to evaluate the cell deformation. A fitting formula between the cell deformation degree and the initial cell parameters is obtained, which can predict the cell deformation degree. It is found that a cell with small anisotropy, large angle between the longest axis of the cell and the loading direction, small sphericity, more neighbors, and large cell size is more prone to deform during compression. With the fitting formula, the weakest region where the first batch of deformed cells occurs can be predicted. The influence of cell morphology parameters in low porosity aluminum foams is significant and verified by experimental results.

An Experimental and Computational Study of the High-Velocity Impact of Low-Density Aluminum Foam.

The study presents the results of an experimental and computational study of the high-velocity impact of low-density aluminum foam into a rigid wall. It is shown that the aluminum foam samples deformed before hitting the rigid wall because of the high inertial forces during the acceleration. During the impact, the samples deformed only in the region contacting the rigid wall due to the high impact velocity; the inertial effects dominated the deformation process. However, the engineering stress–strain relationship retains its typical plateau shape until the densification strain. The experimental tests were successfully reproduced with parametric computer simulations using the LS-DYNA explicit finite element code. A unique computational lattice-type model was used, which can reproduce the randomness of the irregular, open-cell structure of aluminum foams. Parametric computer simulations of twenty different aluminum foam sample models with randomly generated irregular lattice structures were carried out at different acceleration levels to obtain representative statistical results. The high strain-rate sensitivity of low-density aluminum foam was also observed. A comparison of experimental and computational results during aluminum foam sample impact shows very similar deformation behavior. The computational model correctly represents the real impact conditions of low-density aluminum foam and can be recommended for use in similar high-velocity impact investigations.

Anisotropic convective heat transfer in open-cell metal foams: Assessment and correlations

Open-cell metal foams are promising materials for heat transfer augmentation, due to their tortuosity and high specific surface area. The volume-averaging technique under the assumption of local thermal non-equilibrium between the solid and fluid phases is often used to model devices equipped with open-cell foams; it requires an accurate knowledge of the interfacial convective heat transfer coefficient. Its dependence on the anisotropy of elongated foam cells is investigated numerically in the present work. Four aluminum foam samples with different porosities and equal PPIs are considered; their geometry is reconstructed by means of x-ray computed tomography. Mass, momentum and energy equations for the fluid phase (air) are solved, while the solid phase is accounted for with a uniform heat flux boundary condition. Interfacial convective heat transfer coefficients and Nusselt numbers are predicted. The dependence of the interfacial heat transfer coefficient in the elongation direction on the effective porosity and fluid inlet velocity is pointed out. The comparison of predicted values with those given by correlations from the open literature shows a good agreement. Finally, correlations for the prediction of Nusselt numbers, accounting for the foam anisotropy, are proposed, which can be useful in the study of metal foams.

Modelling and optimization of manufacturing calcium carbonate-based aluminum foam

Recently, closed-cell aluminum foam gained increasing attention in many industrial applications due to its high stiffness compared with its very low density. Enhance the properties of aluminum foam by developing its manufacturing process is very important for both industrial and scientific purposes. In this work, an attempt has been made to enhance the essential characteristics of aluminum foam, i.e., compressive strength and porosity level by optimizing the manufacturing process parameters using statistical techniques. The aluminum foam samples were prepared under various conditions of calcium carbonate content, alumina content, foaming temperature and stirring time based on Screening experimental design. Analysis of variances was performed to evaluate the roles of each factor in influencing on the foam properties and identify their optimum values. In addition, mathematical models based on quadratic regression model were developed to predict the responses. The results revealed that all studied parameters have a significant effect on the properties of the produced foams, however, calcium carbonate content is found to be the most effective factor in the process. The optimization results showed the ability to produce high quality aluminum foams with 2.86 MPa compressive strength and 80.4% porosity level by using the optimized fabrication parameters and these results have a permissible error percentage compared with the experimental results.

Static and dynamic analyses of aluminum foam geometric models using the homogenization procedure and the FEA

This paper presents static and dynamic analyses of closed and open cell aluminum foam geometric models using the homogenization technique and the FEA. The RVE models were designed with regard to: the pore size, cell wall and foam porosity of aluminum foam samples. Static analyses of foam cubes were performed in order to obtain the elastic moduli of the analyzed models. The obtained data was afterwards used for the modal analyses. Two types of models: homogenized beam models and optimized-homogenized beam models; and three types of structures: simple beam, sandwich beam and double sandwich beam were used for these analyses. The purpose of the optimized-homogenized model is to save design and calculation time. The results showed that at lower frequencies the models (homogenized beam and optimized-homogenized beam) reach similar natural frequencies and mode shapes. At higher frequencies the geometric shape and the geometric flaws have a big influence on the results.

Enhanced Aluminium Foam Based Cylindrical Sandwiches: Bending Behaviour and Numerical Modeling

Closed-cell aluminium foams are a relatively new class of structural and functional materials that have attracted increasing attention, for which they are candidate materials in many applications of several industrial fields. One of the aims of the research can be the improvement of the mechanical behaviour of foam-based structures by means of reinforcements that preserve their peculiar property of lightness. In view of this challenge, the present paper describes the production, the mechanical characterization and the numerical modelling of enhanced aluminium foam samples. More specifically, cylindrical sandwiches, characterized by a closed-cell aluminium foam core reinforced with a skin of lightweight aluminium alloy wire mesh embedded into a matrix of low porosity foam, were produced in a one step process; therefore, mechanical three point bending tests were carried out, in order to compare the properties of these innovative sandwiches with plain foam cylinders. The results of the experimental campaign highlight a significant improvement of the mechanical properties of the samples, when so reinforced. Moreover, a FEM numerical model of the cylindrical sandwiches was developed and validated, by comparing the simulations with the results of the experimental tests.

Enhancement of heat exchanger thermal hydraulic performance using aluminum foam

This paper deals with an experimental study of a turbulent forced convection in a rectangular channel partly fitted with aluminum metallic foam blocks. Experiments were carried out on samples having a constant porosity of 93.8%, different grades of 5, 20 and 40 PPI, and three different height ratios of 0.6, 0.8 and 1. The blocks were arranged in a baffle like configuration. A constant heat flux of 2 W/cm2 was applied on the bottom wall of the test section, while air velocity was varied from 1 to 5 m·s−1. Temperatures of the wall along the flow direction as well as those of the inlet and outlet sections have been measured. Additionally, pressure drop measurements across the aluminum foam samples were performed. The results showed that there is an optimal choice of the height and the grade of the metal foam for which the heat transfer and pressure drop (for an optimal design of heat exchangers) to reach the design goal. Moreover, this configuration was compared to solid fins aluminum baffles widely used in heat exchangers.

Closed Cell Aluminium Foams with Phase Change Material

Closed cell aluminium foam samples and panels with phase change material (PCM) infiltrated in vacuum were investigated. The utilization of PCMs in larger volumes is strongly limited because of its low thermal conductivity in liquid state. However, porous structure of aluminium foam allows to absorb or to dissipate very homogenously latent heat at almost constant temperature if PCMs with phase change at the temperature range between 4°C and 28 °C are used inside of foam. Therefore the degree of filling of closed cell aluminium foams with PCM material was investigated. It was shown that it is possible to fill sufficient amount of pores with PCM. Further, aluminium foam panels with PCM were tested for heating/cooling applications in buildings. It was confirmed, that such foam panels provide an excellent alternative for large built-in ceiling radiators for efficient heating or cooling of rooms using low potential energy resources. These features of foam panels allow significantly reduce energy consumption of heating/air conditioning systems of future zero energy buildings.

Fire resistance and mechanical properties of enamelled aluminium foam

Aluminium foams show very interesting properties for a wide range of applications, in particular good mechanical properties and fire resistance. The particular cellular structure reduces the corrosion resistance of these materials in several environments. The application of a vitreous enamel layer is a possible solution to obtain a good protective barrier that can also improve the resistance at high temperatures. In this work these properties are evaluated for different porcelain enamelled aluminium foam samples. Starting from plate samples of aluminium foam produced by Alporas method, different enamel systems are studied. A frit without vanadium suitable for aluminium substrate was used. Microstructure analysis was made to highlight the adhesion between enamel and metallic substrate, as well as the filling of the open cells and the presence of defects in the glassy layers. The response to flame exposure of enamelled samples was tested in comparison to the uncoated foam. Finally, mechanical properties were studied by 4-points bending tests. This study has shown that the presence of the vitreous enamel coating increases the fire resistance of the aluminium foam. In addition, it was found that the flexural rigidity increases strongly and it is connected with the particle dimension in the frit.

Random equilateral Kelvin open-cell foam microstructures: Cross-section shapes, compressive behavior, and isotropic characteristics

Representative volume elements of random equilateral Kelvin open-cell microstructures were modeled for the open-cell foam. We adopted the periodic boundary conditions developed in our previous research. The quasistatic compression properties of the representative volume elements in random Kelvin open-cell aluminum foam samples, both with different relative densities and different cross-sections of the beams in the structures were investigated. The results show that the features of the stress–strain curves in the representative volume elements with different relative densities and different cross-sections were similar, and the relationships between the yield strengths and relative densities of representative volume elements with four different cross-sections all agreed well with the quadratic power function. Among the representative volume elements with four different cross-sections, the yield strengths of the representative volume elements with a Plateau border cross-section were significantly larger than in representative volume elements with other cross-sections, while the yield strengths of representative volume elements with circular cross-sections were smaller than in representative volume elements with other cross-sections. This indicates that the simulation results of the compression strengths for open-cell foam in which the representative volume elements with circular cross-sections were employed are significantly smaller than their actual values. The main reason for this is that the moments of inertia in the Plateau border cross-sections are significantly greater than in the circular cross-sections of the same area. Our investigation results revealed that the compression responses of the representative volume elements for random equilateral Kelvin open-cell microstructures demonstrate isotropic behavior on the xoy plane, the yoz plane, and the xoz plane.

Radiation heat transfer in high porosity open-cell metal foams for cryogenic applications

Radiation heat transfer in high porosity open-cell metal foams subjected to cryogenic temperatures has been studied. This study helps designing metal-foam-based devices exposed to radiation of deep space at extremely low temperature. Aluminium and copper foam samples with more than 90% and 95% void volume respectively and pore size in the range of 10–30 PPI have been studied. Suspending the foam samples freely inside a vacuum chamber (at 10−6mbar) and maintaining the chamber wall at liquid nitrogen temperature, the cool down time–temperature profiles has been recorded for nearly 5.5h, wherein different foams reach temperatures in the range of 119–128K. Simultaneously, theoretical model based on lumped-capacity analysis has been developed to simulate the transient behaviour of foam samples. Simple cubic structure foam model has been used to estimate the view factor. The experimental outcome could be predicted by the theoretical model with reasonable accuracy. Additionally, cool-down history of an aluminium foam sample has been compared to a solid body of same weight so as to appreciate their radiative potential at low temperatures.