An aluminum foam sandwiches (AFSs) consisting of ADC12 Al-Si-Cu die casting aluminum alloy foam and ADC6 Al-Mg die casting aluminum alloy face plates were fabricated. Using ADC12 die casting plates containing large amounts of gases as the starting material of the foam, ADC12 foam can be fabricated without using a blowing agent. Using FSW, both the uniform dispersion of the segregated gases and pore stabilization powder in the ADC12 die casting plates used to fabricate a foamable ADC12 precursor and the bonding of the ADC12 precursor to the ADC6 plates can be simultaneously achieved. Namely, the AFS precursor is expected to be obtained in fewer processing steps. From the visual observation of the fabricated AFSs, no deformation of the ADC6 plates occurred and the ADC6 plates on both sides of the aluminum foam remained parallel. From the X-ray CT observation of the fabricated AFSs, good pore structures without the infiltration of ADC12 foam into the ADC6 plates can be obtained at a holding temperature of 948 K and holding times of t = 10 and 11 min. In tensile tests on the fabricated AFSs, fracture occurred in the ADC12 foam parts but no fractures were observed at the bonding interface between the ADC12 foam and the ADC6 plates, that is, good bonding was obtained between the ADC12 foam and the ADC6 plates.

Al foam has been used in a wide range of applications owing to its light weight, high energy absorption and high sound insulation. One of the promising processes for fabricating Al foam involves the use of a foamable precursor. In this study, ADC12 Al foams with porosities of 67%–78% were fabricated from Al alloy die castings without using a blowing agent by the friction stir processing route. The pore structure and tensile properties of the ADC12 foams were investigated and compared with those of commercially available ALPORAS. From X-ray computed tomography (X-ray CT) observations of the pore structure of ADC12 foams, it was found that they have smaller pores with a narrower distribution than those in ALPORAS. Tensile tests on the ADC12 foams indicated that as their porosity increased, the tensile strength and tensile strain decreased, with strong relation between the porosity, tensile strength, and tensile strain. ADC12 foams exhibited brittle fracture, whereas ALPORAS exhibited ductile fracture, which is due to the nature of the Al alloy used as the base material of the foams. By image-based finite element (FE) analysis using X-ray CT images corresponding to the tensile tests on ADC12 foams, it was shown that the fracture path of ADC12 foams observed in tensile tests and the regions of high stress obtained from FE analysis correspond to each other. Therefore, it is considered that the fracture behavior of ADC12 foams in relation to their pore structure distribution can be investigated by image-based FE analysis.

Al foam is expected to be used as automotive components because of its light weight as well as its good energy absorption properties. When Al foam is applied to automotive components with complicated shapes, it is desirable to optimally distribute the low-plateau-stress and high-plateau-stress regions in a single Al foam, such as functionally graded (FG) Al foam, to realize components with superior and efficient energy absorption properties. In this study, two types of closed-cell FG Al foam, one composed of larger-smaller-larger three layers with different porosity and pore size to indicate lower-higher-lower plateau stress, and the other composed of smaller-larger-smaller three layers with different porosity and pore size to indicate higher-lower-higher plateau stress, were fabricated by varying the amount of blowing agent added. It was shown that the large-porosity and large-pore-size layers first deformed and, thereafter, the layers with small porosity and pore size deformed, regardless of the location of the large-porosity and large-pore-size layers in the compression test specimens. It was also shown that the first (lower) and second (higher) plateau regions appeared independently, which corresponds to the pore structures of each layer. Therefore, it was demonstrated that the plateau stress of Al foam can be controlled by varying the pore structures.