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The stir casting technique was used to produce A356 alloy composite foams reinforced with different volume fractions of mullite (5, 7.5, 10, and 12.5%) and SiC (5, 7.5, 10, and 12.5%) particles. The microstructure of the fabricated foams reveals a uniform distribution of these particles within the cell walls, as well as good interfacial interaction with the alloy matrix. Compressive stress–strain curves of the composite foam increase smoothly with strain, and there is very marginal stress oscillation occurred in the plateau region of foam throughout the test. It is worth noting that, regardless of foam composition, plateau stress and energy absorption of foams follow power-law relationships with relative density, while densification strain follows a linear trend with relative density. Furthermore, as compared to the SiC particles reinforced composite foams, the mullite reinforcement exhibits higher plateau stress and energy absorption. [ABSTRACT FROM AUTHOR]

In the present work, open-cell aluminum-reduced graphene oxide composite (Al-rGO) foam with varying concentrations of reduced graphene oxide (rGO) was fabricated through the template method and foam's electrical, mechanical, and electromagnetic shielding behavior was studied. The reticulated Al-rGO foam allows the electromagnetic wave (EMW) to go inside the structure and resulting in multiple scattering which enhances the wave absorption capacity of the material. Adding rGO into open-cell aluminium foam (OCAF) enhances its shielding properties, particularly the absorption component. The Al-rGO3 foam shows a total EMI shielding of ∼62 dB at 8.4 GHz frequency and out of which 61.34 dB (> 99% of total shielding) is the absorption component. The Al-rGO foam also exhibited maximum compressive strength of 2.96 MPa and EMI shielding of ∼62 dB at 1.5 wt% rGO, even though the electrical conductivity reduces with rGO content. This may be due to a greater degree of multiple scattering of EMW inside the cellular structure and different energy losses at rGO-Al interfaces. This work shows a new way to use the lightweight metallic structure for high EMW absorption applications with good mechanical stability in the defense and aerospace sectors. [Display omitted] • Al-rGO in-situ foam made by reduction of Al-GO foam. • The density of the material is 0.45 g/cc, which makes it much lighter. • Higher porosity and interfaces causes EMW absorption coefficient > 98%. • Al-rGO shows two-order higher EMW absorption compared to pure Al. • Al-rGO showed good mechanical, oxidation, and temperature stability. [ABSTRACT FROM AUTHOR]

The hot deformation behaviour of Al-Si12CulMg1 alloy foam, Al-Si12CulMg1 alloy-single-wall carbon nanotubes (SWNTs), Al-Si12CulMg1-cenospheres, and Al-Si12CulMg1-cenosphere-SWNTs hybrid foams (HFs) were investigated at different test temperatures (25–400 °C) and strain rates (10-3-1 s-1) conditions. It is observed that the energy absorption capacity of all the foams decreased with an increased test temperature (TT) whereas it increased with an increase in strain rate. The hybrid foam in which the cenosphere and SWNTs were added together exhibited the highest plateau stress and energy absorption amongst all investigated foams. The strain rate sensitivity and activation energy for each kind of foam was calculated as a function of temperature and strain rate. The activation energy data tells that the deformation mechanism is dominated by vacancy and dislocation diffusion at TT≤ 200 °C regardless of the type of foam, strain rate and relative density. On the other hand, the deformation mechanism is dominated by dynamic recovery and recrystallization when the TT increase beyond 200 °C (TT>200 °C). This study further demonstrates the synergistic effect of cenosphere and SWNTs on enhancing the plateau stress and energy absorption of HFs. • The TT and strain rate effect on the compressive stress-strain response of AFs and HFs. • Detailed analysis of the compressive strength and the energy absorption performances of AFs and HFs as a function of TT and strain rate. • Detailed analysis of effects of TT and strain rates on the activation energy and strain rate sensitivity of AFs and HFs. • Discussion of HFs failure mechanism. [ABSTRACT FROM AUTHOR]

The effect of relative density (RD) and shape of the space holder on microstructural characteristics and compressive behavior of open-cell aluminum foams (OAFs) have been studied. OAFs with tailored porous morphologies (50–81%) were successfully prepared through space holder technique using spherical shape carbamide and cubic shape sucrose space holders in various amounts. Al powder and space holders were mixed with 2 wt% of polyvinyl alcohol (PVA) binder solution, compacted at 300 MPa and finally sintered at 650 °C for 3 h. It was observed that the microstructural characteristics of OAFs varied in accordance with the shapes of space holders. The results reveal that the OAFs prepared with carbamide show smooth microstructure, higher plateau stress (~3 times), higher energy absorption (~3 times) and higher Young's modulus, but lower densification strain, compared to the OAFs prepared with sucrose. The Young's modulus, plateau stress, and energy absorption of OAFs, follow the power-law relationship as a function of its RD irrespective of the shape of space holders. The thermal conductivity of Al-carb and Al-suc OAFs are noted to be not much in variation irrespective of the shape of the pores. [Display omitted] • Open-cell Al-carb and Al-suc foams were successfully prepared by space holder technique using powder metallurgy route. • Al-carb foams exhibit uniform pore distribution having smooth cell-walls with less micro-defects than Al-suc foams. • Al-carb foams have higher plateau stress (~3 times), energy absorption (~3 times) and Young's modulus than Al-suc foams. • Young's modulus, plateau stress and energy absorption for both foams follow power-law relationship with RD. [ABSTRACT FROM AUTHOR]

• The stress-strain responses of aluminium and hybrid aluminium foam for various relative density and strain rate sensitivity have been analyzed in the strain rates range of 10−3 to 1500 s−1 at room temperature. • The energy absorption capacity of Al-cenosphere-SWNTs hybrid foam increases significantly with relative density and strain rate. • Irrespective of foam composition, strain rate sensitivity and strength constant for maximum stress is comparatively higher than the plateau stress. • The energy absorption efficiency of hybrid aluminium foam for a fixed value of strain rate does not follow any particular trend of variation with an increase in relative density. • The average plateau stress of aluminium and hybrid aluminium foam follow power-law relation with relative density, whereas densification strain follows a linear connection with relative density. In the present study, single-walled carbon nanotubes (SWNTs) and cenosphere reinforced closed cell hybrid aluminium foams (HAFs) of varying relative densities were produced, and their compressive deformation behaviour at different strain rates have been examined. The addition of SWNTs leads to a significant increase in plateau stress, plastic collapse stress, and energy absorption. This may be due to higher dislocation density and finer inter-SWNT spacing. The Raman spectra of HAFs showed the uniform distribution of SWNTs in the cell wall region. However, the effect of quasi-static strain rates (10−3 to 10 s−1) on the compressive deformation response is marginal. While the influences of higher strain rate ranges (10−3 to 1500 s−1) are considerably higher than the quasi-static strain rate range. The strain rate sensitivity of these foams is much less than unity (~0.0088-0.0314), indicating the brittle nature of foam deformation. The plastic collapse, plateau stress, and energy absorption of HAFs increase significantly with an increase in relative density. Interestingly, it is observed that both plateau stress and energy absorption follow power-law relation with relative density, and densification strain follows a linear relation with relative density irrespective of strain rate and foam material. It is further noted that the strain rate sensitivity of HAFs increases marginally with relative density. The deformation mechanism of HAFs has been examined using the digital photographs captured during the uniaxial compression test and the SEM, TEM images of deformed specimens. [Display omitted] [ABSTRACT FROM AUTHOR]

• Partially open cell Ti6Al2Co ternary alloy foams was prepared using range of particle size and volume fraction of sapcer particles. • The decrease of size and increase of vol% of spacer particles decreased the plateau stress, modulus, toughness and microhardness. • The mechanical properties followed power laws and constants of proportionality, and exponent values were found in the close agreement with the published data. • Corrosion rates (mmpy) have been increased with the decrease of particle size of spacer particles. Partially open cell Ti-6Al-2Co alloys foams of varying cell (pore) size (0 to 500 µm) and volume fraction (40 to 70%) are made by varying the space-holder size (SHS) and volume fraction. The increase of space-holder (spacer) size increased the cell size and cell-wall thicknesses, which led to increased plateau stress, energy absorbed (Toughness), hardness and Young's modulus. Further, increased spacer content and decrease of strain rate; reduced the strength, toughness, and modulus of Ti6Al2Co ternary alloy foams. The corrosion rate was found to be decreasing with increase of particle size of space-holder Also, the corrosion rate and weight loss percent increases with increase in cell volume fraction. Further, the Ti6Al2Co alloy foam's mechanical properties were found to have a trend of power-law relations with relative densities. [ABSTRACT FROM AUTHOR]