Compressive properties of two-layered aluminum foams with closed-cell and open-cell structures

Multilayered Al foams with tailored properties are a new class of functionally graded materials that exhibit position-dependent properties and superior mechanical properties to uniform Al foams. In this study, twolayered Al foams with closed-cell and open-cell structures and various porosities were fabricated. The open-cell structure layer was formed by a sintering dissolution process and the closed-cell structure layer was formed by a precursor foaming process. During the foaming process of the upper precursor layer, it was found that the combination of the lower melting point AC4CH alloy for the upper layer and the relatively high melting point pure Al for the lower layer prevents the collapse of lower layer. Also, by varying the foaming time, two-layered Al foams with various porosities of the upper AC4CH foam layer can be obtained. During compression tests, the two-layered Al foams exhibited two-step deformation. Two plateau regions with different strengths were observed in the stress - strain curves, corresponding to the two-step deformation. The plateau stress of the AC4CH foam layer was similar to that of uniform AC4CH foam with similar porosity. Similarly, the plateau stress of the pure Al foam layer was similar to that of uniform pure Al foam. Therefore, it was found that Al foams with similar porosities exhibited similar plateau stress regardless of the foam being a two-layered Al foam or uniform Al foam. In addition, the plateau stress of each layer decreased as its porosity increased, with the relationship having a strong correlation, regardless of the first or second plateau region.