Abstract: In this work, we synthesized a brand-new Al foam with a periodic structure via a simple powder metallurgical route. The periodic architecture consists of both hierarchical porous and bi-directional composition-graded structures. The results show that the hierarchical porous material includes large pores on millimeter scale inheriting from the hollow structure of the Al tubes, and small pores on micrometer scale produced by the sintering of Al/Mg powders. The bi-directional Mg concentration-graded structure is formed in the tube walls due to the condensation of Mg vapor in the inner tube wall. The addition of Mg powders achieves excellent metallurgical bonding between the Al powders and the hollow tubes at 550°C. The plateau stress and energy absorption capacity of the Al foam in y-axis compression are significantly higher than that in the x-axis due to their anisotropic structure. In general, the Al foam with Mg addition presents the most superior compression performance, and we believe that our findings could open up a unique strategy for developing high-performance metallic foams with the periodic architecture involving both hierarchical porous and bi-directional graded structure.

Key words: Al foam, Hollow Al tube, Mg evaporation, Bi-directional composition-graded structure, Compression properties, Energy absorbing performance