Al tubes filled with Al foam were fabricated by friction stir back extrusion (FSBE), which can realize metal bonding between the foam and tube. In this process, an Al tube was first fabricated from bulk Al. Next, foamable precursor was coated on the surface of the inner wall of the fabricated tube. Thereafter, the tube coated with the precursor was heat-treated to foam the precursor, thus obtaining a tube filled with foam. In the tube fabrication process, it was found that a tube can be fabricated from a block with no defects and similar compression responses to that of a tube fabricated by a machining process. For the foaming process, it was found that the bonding of the precursor and tube induces strong bonding between the foam and tube. Regarding the compression properties of the tube, it was found that the foam-filled tube exhibited superior compression properties to empty tubes and foams. In particular, during compression tests, a decrease in the stress in stress–strain curves for an empty tube due to the generation of a fold can be avoided by filling the tube with foam filler with metal bonding between the foam and tube.
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