Owing to its lightweight and excellent shock-absorbing properties, aluminum foam is used in automotive parts and construction materials. If a nondestructive quality assurance method can be established, the application of aluminum foam will be further expanded. In this study, we attempted to estimate the plateau stress of aluminum foam via machine learning (deep learning) using X-ray computed tomography (CT) images of aluminum foam. The plateau stresses estimated by machine learning and those actually obtained using the compression test were almost identical. Consequently, it was shown that plateau stress can be estimated by training using the two-dimensional cross-sectional images obtained nondestructively via X-ray CT imaging.

A mixture of Al burrs of Al high-pressure die-castings and a blowing agent powder was used to fabricate Al foam-filled steel tubes by friction stir back extrusion (FSBE). It was shown that the mixture can be sufficiently consolidated to form an Al precursor that is coated on the inner surface of a steel tube by the plastic flow generated during FSBE. Namely, a precursor coated steel tube can be fabricated from Al burrs by FSBE. By heat treatment of the precursor coated steel tube, an Al foam-filled steel tube can be fabricated. Al foam was sufficiently filled in the steel tube, and the porosity was almost homogeneously distributed in the entire sample. In compression tests of the samples, the Al foam-filled steel tube fabricated from Al burrs exhibited similar compression properties to an Al foam-filled steel tube fabricated from the bulk Al precursor. Consequently, it was shown that an Al foam-filled steel tube cost-effectively fabricated from Al burrs by FSBE compares favorably with an Al foam-filled steel tube fabricated from the bulk Al precursor.

Aluminum foam is attracting attention as a multifunctional, ultra-lightweight material. To apply this aluminum foam to actual industrial materials, aluminum foam plates are required. In addition, it is expected that a multi-layer aluminum foam composed of dissimilar aluminum alloy foam layers can further enhance its functionality. In this study, we attempted to fabricate a three-layer aluminum foam composed of commercially pure aluminum AA1050 and Al-Mg-Si aluminum alloy AA6061 by heating and foaming a total of three pieces of AA1050 precursor and AA6061 precursor arranged alternately, followed by immediate roller joining. It was found that, by traversing a roller immediately after foaming the AA1050 and AA6061 precursors, the aluminum foam could be joined while forming it into a flat plate. In addition, X-ray CT images of the fabricated samples revealed that material flow induced by roller traversing ruptured the surface skin layer. Numerous pores were observed within the sample, indicating pores were maintained during the roller traversing and no significant differences in porosities were identified between AA1050 aluminum foam and AA6061 aluminum foam. Furthermore, from the four-point bending test and the observation of samples after bending test, although quantitative mechanical properties were not obtained due to the as-joined samples were used for the bending test, pores were observed at the fracture surfaces, confirming that roller joining achieved seamless joining.