Closed-cell Aluminum Alloy Foams Research Articles

Nonlinear low-velocity impact analysis of sandwich plates with titanium face sheets and porous aluminum core reinforced by GPLs

This study examines the nonlinear dynamic response of sandwich plates under low-velocity impacts (LVIs), which consist of a porous aluminum foam core with functionally graded (FG) graphene platelets (GPLs) reinforcement and two titanium alloy face sheets. The finite element method is employed to perform the numerical simulations and the Hertz contact theory is used to model the impact behavior. The generic Halpin-Tsai model, which incorporates the porosity effect, is adopted to estimate the mechanical properties of core made of the FG-GPLRC, based on the experimental data of the closed-cell aluminum alloy foam. The simulation results reveal that the FG-X configuration has the highest impact resistance, and that the addition of GPLs improves the impact performance. Moreover, a thicker core can reduce both the first contact time and the vibration period of plates, while a looser boundary condition can prolong the vibration time after the first impact. Additionally, a higher impactor velocity, mass and radius lead to a higher deflection and contact force. The oblique impact decreases the impact energy. This work provides a lighter and stiffer design for structure engineers when components suffer low-velocity impact.

Effect of Mg Content Change on the Production of Closed-Cell Aluminum Alloy Foam by Selective Laser Melting

Effect of Mg Content Change on the Production of Closed-Cell Aluminum Alloy Foam by Selective Laser Melting

Nonlinear low-velocity impact response of sandwich beams with FG porous aluminum core reinforced by GPLs

Sandwich beam structures facing low-velocity impact frequently throughout their life cycle, making it necessary to investigate the impact response of these structures to enhance their design and reliability in service. In this paper, sandwich beam structures subjected to nonlinear low-velocity impacts are investigated, comprising a functionally graded (FG) porous aluminum core reinforced by graphene platelets (GPLs) and two aluminum alloy face sheets. The mechanical properties of FG-GPLRC core are predicted by a generalized Halpin-Tsai model, which takes porosity into account, where the material properties of the closed-cell aluminum alloy foam are established on experimental data. The numerical investigations are conducted using the finite element method and apply the Hertz contact law. The simulation results indicate that the FG-X pattern, where the porosity coefficients are designed to have the maximum values at the top and bottom layers, while to have the minimum values at the mid-plane layers, exhibits the best impact resistance, and that the incorporation of GPLs enhances the impact response. Furthermore, the findings suggest that the thickness of the core has no impact on the duration of the initial impact. Moreover, an increase in impactor velocity, density and radius results in an increase in both deflection and contact force.

Production of Refined and Modified Closed-Cell Aluminum Foams by Melt-Foaming Method

Closed-cell A356 aluminum alloy foams refined and modified were successfully fabricated by using barite and calcium carbonate as thickening and foaming agents, respectively. A melt treatment consisting of adding master alloys of Al-5Ti-1B and Al-10Sr for refining the dendritic microstructure and modifying the primary eutectic silicon, respectively, were included in the foaming process. The microstructure and mechanical properties of the foams manufactured were analyzed and compared with foams produced without the refining and modifying treatments. The secondary dendritic arm spacing (SDAS) was determined by optical measurements. Lower SDAS values were obtained in foam regions closer to the mold walls due to the high solidification rate imposed during the cooling step and a decrease in the SDAS values for the foams produced with the addition of the Al-5Ti-1B master alloy was evident. Additionally, the addition of the Al-10Sr master alloy caused the formation of solid solution dendrites and a fine irregular fibrous form of silicon. Foams produced with the melt treatment exhibit a good combination of structure and mechanical properties. Therefore, the melt route established is a feasible way to improve foam performance where the lowest SDAS and the highest mechanical properties were obtained for the closed-cell foams produced.

Effect of Laser Forming on the Energy Absorbing Behavior of Metal Foams

Abstract Metal foam is light in weight and exhibits an excellent impact absorbing capability. Laser forming has emerged as a promising process in shaping metal foam plates into desired geometry. While the feasibility and shaping mechanism has been studied, the effect of the laser forming process on the mechanical properties and the energy absorbing behavior in particular of the formed foam parts has not been well understood. This study comparatively investigated such effect on as-received and laser formed closed-cell aluminum alloy foam. In quasi-static compression tests, attention paid to the changes in the elastic region. Imperfections near the laser irradiated surface were closely examined and used to help elucidate the similarities and differences in as-received and laser formed specimens. Similarly, from the impact tests, differences in deformation and specific energy absorption were focused on, while relative density distribution and evolution of foam specimens were numerically investigated.

Impact of the reinforced metal structure on the mechanical properties foamed aluminium composites at the load

Abstract This paper is an experimental study of the quasi-static mechanical compressive properties of the reinforced closed-cell aluminum alloy foams with different cell orientations at different strain rates. The reinforced foam samples were obtained via the powder metallurgical route. The results of the compression tests revealed that the deformation behavior and mechanical properties of foamed aluminum composites are highly dependent on the orientation of the reinforcing mesh. Differences in the deformation behavior of foams appear to be influenced by the mechanical properties of the matrix material, by foam deformation mechanisms, and by the mechanical properties of the reinforcement. The yield stress, plateau stress, densification stress, and energy absorption capacity of unreinforced foam samples improved linearly with increasing strain rate due to dynamic recrystallization and softening of the foam matrix material. The reinforced foam samples exhibit nonlinear deformation behavior. It was also found that the mechanical properties reduction of transverse reinforced foams was slightly lower compared to foams with longitudinal reinforcement at varying strain rates because of the large contribution of the mechanical properties of the reinforcement. The results of the present study can be employed to modelling and obtain impact-resistant fillers for complex structures in transport construction.

Effect of in situ Al3Zr particles on controlling the pore morphology of Al6061 alloy foams

Mechanical properties of closed cell aluminium alloy foams are mainly dependent on their cell structure. The cell structures are typically affected by the foaming agents and composite particles. Several studies have reported processing and properties of composite foams, that are mostly ex situ, however, the influence of in situ composites on foaming, particularly Al3Zr particles which are known have better wettability, is scarcely reported. The focus of the present study was to investigate the effect of in situ Al3Zr particles on controlling the pore size of Al6061 alloy foams fabricated via liquid metallurgy. The cell structures of Al3Zr/Al6061 in situ composite foams and the conventional Al6061 alloy foams were quantitatively analyzed using X-ray tomography. The presence of in situ Al3Zr particles resulted in significant reduction in the average pore size, as well has enhancement in the density and size-distribution of the pores size when compared with the conventional Al6061 alloy foams. Static compression tests showed improvement in the peak strength, average compressive strength, and the energy absorption capacity in aluminium alloy foams

Anisotropic Compressive Behavior of Metallic Foams under Extreme Temperature Conditions.

Metallic foams find their applicability in complex systems that operate under both real-life conditions (Earth living conditions) and extreme temperature conditions (low or high temperatures). In this paper, the main mechanical properties of closed-cell aluminum alloy (A356) foams under quasi-static compression loading conditions were determined. In order to investigate the compressive behavior, three orthogonal directions (X, Y, and Z) and three testing temperatures (−196, 25 and 250 °C) were considered. It has been observed that the temperature significantly influences the strength properties and energy absorption performances of the aluminum metallic foams AMFs. Moreover, it was found that microstructural characteristics, such as intrinsic defects (intracellular cavities, micro-pores and thin cell-walls) and structural anisotropy (shape, size and orientation of cells), play a decisive role in the mechanical behavior of AMFs. Moreover, the paper compares the relative percentage change (relative percentage increase and decrease) of the main normalized compressive properties (yield stress, plateau stress, densification stress and the energy absorption) of AMF samples, according to testing temperature and loading direction.

Bending performance evaluation of aluminium alloy tubes filled with different cellular metal cores

A comprehensive bending performance and energy absorption capability of aluminium alloy tubes filled with different cost-effective cellular metal cores were experimentally evaluated for the first time. The following cellular metal cores were evaluated: i) Advanced Pore Morphology (APM) foam, ii) hybrid APM foam and iii) Metallic Hollow Sphere Structures (MHSS). The results have been compared also with the performance of aluminium alloy tubes filled with (ex-situ and in-situ) closed-cell aluminium alloy foam. The three-point bending tests have been performed at two loading rates (quasi-static and dynamic) and supported by infrared thermography to evaluate the deformation mechanism, damage progress and failure modes. A thorough heat treatment sensitivity (due to the fabrication procedures of composite structures) study on the aluminium tubes has been performed as well. The results show that a reliable and predictable mechanical behaviour and failure can be achieved with proper combination of tubes and cellular metal core. A low scatter of bending properties and energy absorption capability has been observed. The hybrid APM and the ex-situ foam filled tubes achieved the highest peak load. However, they also exhibit a rapid load drop and abrupt failure once the structure has reached the peak load. The APM, MHSS and in-situ foam filled tubes show more ductile behaviour with a predictable failure mode.

Cryogenic and high temperature compressive properties of Metal Foam Matrix Composites

The cryogenic (−196 °C), room (25 °C) and high (250 °C) temperature compressive crushing performances of recently developed metal foam matrix composites was investigated with respect to the position of reinforcements on foam samples. Closed-cell aluminum alloy foams were produced via powder metallurgical route from AlSi10 matrix material; while diamond shape expanded stainless steel were used as reinforcements. The deformation behavior and main mechanical properties of the unreinforced and reinforced metallic foam was found to be strongly temperature dependent under quasi-static loading. Reinforced foams exhibited much higher strength properties and energy absorption capability compared to unreinforced foams at almost the same overall weight of the samples, i.e. up to 11 times. The properties percentage reductions of the reinforced foams are significantly below the reduction of the unreinforced foam. Furthermore, it was observed that the collapse mechanisms and mechanical properties of the reinforced foams depends on reinforcement position.

The effect of thermal processing parameters on the mechanical properties of aluminium alloy foam

Purpose: The purpose of this study was to investigate the influence of three thermal processing parameter called stress relieving on mechanical properties of the aluminium alloy foam. Design/methodology/approach: The samples were undergone by stress relieving method using vacuum furnace. Hardness measurement was carried out using microhardness Vickers at 150 mN load and 15 s loading time. Compressive strength, plateau stress and energy absorption were calculated using a universal testing machine. Findings: It was found that the highest value of hardness of 192.78 Hv was obtained when the stress relieving process is set with the following parameters: heating (500°C); holding time (120 min) and stabilization temperature (450°C). Since higher heating temperature and longer holding time produce sample with larger grain size and has an adverse effect on the hardness value It was revealed that the mechanical properties of aluminium alloy foam were enhanced when the heating temperature was decreased, holding temperature was diminished and the stabilization temperature was increased. Overall, the presented results showed that the thermal processing parameters such as heating temperature, holding time and stabilization temperature have a significant influence on improving the mechanical properties of aluminium alloy foam. Research limitations/implications: The properties of closed-cell aluminium alloy foam are highly sensitive and depend on the post heat treatment process. The processing parameters should be controlled in order to manipulate the properties of closed-cell aluminium alloy foam. Originality/value: To investigate the influences of these processing parameters on the physical and mechanical properties of the closed-cell aluminium alloy foam.

Compressive Behavior and Energy Absorption Capability of Reinforced Closed-Cell Aluminum Alloy Foams

In recent years aluminum foams and lightweight composite structures with foam core became popular in aerospace as well as in the automotive industry, because of their unique mechanical properties combined with a very low density. This paper investigates and compares the mechanical behavior, the collapse modes and energy absorption capability of unreinforced and reinforced (with 2 different reinforcement positions) aluminum foam composite structures. Quasi-static compressive tests have been undertaken under three different directions and the reinforcement effect on the main mechanical properties (Young’s modulus, yield stress, plateau stress and densification) was investigated. The tested closed-cell aluminum alloy foams with a density of 325 kg/m3 were reinforced with stainless steel mesh. It has been shown that the compression strength and energy absorption performances of the composite foams can be optimized through the correct positioning of the reinforcements.

Additive manufactured closed-cell aluminum alloy foams via laser melting deposition process

Compared with traditional preparation methods to fabricate aluminum foams, additive manufacturing technology have some advantages such as the ability to prepare complex shapes and relatively high processing efficiency. In this paper, laser melting deposition (LMD) process has been used to additive manufacture aluminum alloy foams (AAFs). During LMD process, Ni-coated TiH2 was used as the foaming agent. AAFs with different porosity and pore-size have been manufactured by LMD process. The pore size and porosity of AAFs are increasing with increasing addition of Ni-TiH2. The sound insulation measurement results indicate that porosity and pore-size have influence on sound-insulated capability. With pore size and porosity increasing, sound-insulated capability of AAFs show a trend of decreasing at first and increasing later.

Effect of the large cells on the fatigue properties of closed-cell aluminum alloy foam

The effect of the large cells on the fatigue properties of closed-cell aluminum alloy foam is studied experimentally and numerically. To do this, a parameter termed as characteristic diameter (Dch) is introduced. 44 dog-bone type specimens are tested with MTS fatigue test machine. In addition, the fatigue performances are numerically simulated by using foam models generated with a program given in this paper. In both cases, large scatter in fatigue life is observed. After classifying the foams into different groups based on their Dch, the fatigue life results of foams within the same Dch range show smaller diversity. It indicates that Dch is an effective parameter which can be used to classify the fatigue performance of foam materials. For foams with same relative density, foams with higher Dch are inclined to have shorter fatigue lives, even though the cell size distributions of foams are different. It is concluded that the fatigue life of foam is dominated by the large cells rather than the cell size distribution. By observing the fatigue life contour obtained from numerical simulation, the dangerous regions in the cell structure are found near the cell walls of larger cells and on the outer surfaces of foam.

On the Lateral Compressive Behavior of Empty and Ex-Situ Aluminum Foam-Filled Tubes at High Temperature.

In this research work, the effect of lateral loading (LL) on the crushing performance of empty tubes (ETs) and ex situ aluminum foam-filled tubes (FFTs) was investigated at 300 °C. The cylindrical thin-walled steel tube was filled with the closed-cell aluminum alloy foam that compressed under quasi-static loading conditions. During the compression test, the main mechanical properties of the ETs improved due to the interaction effect between the cellular structure of the foam and the inner wall of the empty tube. In addition, the initial propagated cracks on the steel tubes reduced considerably as a result of such interaction. Furthermore, the obtained results of the LL loading were compared with the axial loading (AL) results for both ETs and FFTs at the same temperature. The findings indicated that the application of loading on the lateral surface of the composite causes the lower mechanical properties of both ETs and FFTs in comparison with the axial loading conditions.

Axial crush behaviour of the aluminium alloy in-situ foam filled tubes with very low wall thickness

This paper presents the results of an experimental work carried out to fabricate and characterise the in-situ foam filled tubes (FFTs) made of aluminium alloys prepared by powder metallurgy method, using aluminium alloy tubes with extremely thin walls (∼0.6 mm). The fabrication procedure demonstrates that thin-walled tubes with extremely thin walls can support temperatures near to its melting temperature (∼700 °C) required to form a closed-cell aluminium alloy foam, consequently in-situ filling the tube. The mechanical performance of fabricated structures was evaluated using uniaxial compressive tests and infrared thermography. Results demonstrate that the benefits of the manufacturing process and its product, the FFTs (composite structures). Additionally, they reveal that this is a cost-effective solution to prepare efficient energy absorbing lightweight structures, allowing to adjust the weight and levels of the energy absorption, simultaneously. The results demonstrate that the promising in-situ FFTs with thinner outer tubes axially deform in an efficient mixed mode, showing superior energy absorption capability compared to the empty thin-walled tubes.

Thermodynamic analysis of the aluminum alloy foaming process by melt route

A thermodynamic analysis was carried out to determine the stability compounds formed by the interaction between the molten alloy (A356 alloy) with a foaming agent (1, 2, 3 wt. % CaCO3) and a thickening agent (1 wt. % Al2O3) for the production of closed-cell aluminum alloy foams. Stability phase diagrams were obtained to 973, 1073 and 1173 K and they showed the formation of the compounds MgAl2O4, CaAl4O7, Al4C3, and Al4O4C. Typical closed-cell foams of the A356 aluminum alloy were produced to the same conditions of the thermodynamic analysis. The structure of the foams produced was evaluated by SEM-EDS and Raman techniques. The stability compounds predicted are in good agreement with those determined experimentally. The compounds formed by the interaction between the particles and the melt were increased with the increase of the foaming agent and were located at the cell walls.

The temperature and anisotropy effect on compressive behavior of cylindrical closed-cell aluminum-alloy foams

In this paper, the main mechanical properties of the closed-cell aluminum-alloy foams under different quasi-static loading conditions and different temperatures (25, 150, 300 and 450 °C) were experimentally investigated. In order to illustrate the effect of anisotropy, two loading positions of the cylindrical foam samples, axial and lateral (20 mm diameter and 20 mm height), during the compressive loads, were considered. The results showed a decrease in mechanical properties of the foam material, for both axial and lateral loading conditions, with increasing the temperature during compression tests. Also, it was found that at all tested temperatures, the porous structure, when compressed laterally, tolerates the lower level of loads and energy absorption in comparison to axial loading. Finally, it was observed that the main mechanical properties in axial loading direction are more affected by the increase of the testing temperature than lateral one.

The Temperature Effect on the Compressive Behavior of Closed-Cell Aluminum-Alloy Foams

In this research, the mechanical behavior of closed-cell aluminum (Al)-alloy foams was investigated at different temperatures in the range of 25-450 °C. The main mechanical properties of porous Al-alloy foams are affected by the testing temperature, and they decrease with the increase in the temperature during uniaxial compression. From both the constant/serrated character of stress–strain curves and macro/microstructural morphology of deformed cellular structure, it was found that Al foams present a transition temperature from brittle to ductile behavior around 192 °C. Due to the softening of the cellular structure at higher temperatures, linear correlations of the stress amplitude and that of the absorbed energy with the temperature were proposed. Also, it was observed that the presence of inherent defects like micropores in the foam cell walls induced further local stress concentration which weakens the cellular structure’s strength and crack propagation and cell-wall plastic deformation are the dominant collapse mechanisms. Finally, an energy absorption study was performed and an optimum temperature was proposed.

Mechanical response and dynamic deformation mechanisms of closed-cell aluminium alloy foams under dynamic loading

The dynamic compressive response of closed-cell (CYMAT™) stabilised aluminium alloy foams (SAF) has been investigated using a modified Split Hopkinson Pressure Bar (SHPB) in conjunction with a high-speed camera. Tests have been carried out on 45 mm diameter and 23 mm thick cylindrical specimens. The elastic-plastic pore collapse mechanism has been investigated using Digital Image Correlation (DIC) and micro-computed X-ray tomography. A stress-strain relationship for individual specimens at different impact velocities has been obtained with the combination of an analytical method and SHPB theory. The large deformation (∼80%) has been measured from eight strain gauges’ data using a wave separation algorithm. The test results exhibited a significant increase in elastic and plastic strength during the pulse loading. The X-ray tomography data of pre-impacted and post-impacted SAF specimens have been extensively analysed to elucidate the internal elastic-plastic pore collapse mechanisms.