Fabrication of porous aluminum with controllable open-pore fraction

Aluminum with an open-pore structure was fabricated through nitridation of an AA6061-2 pct Mg-1 pct Sn powder mixture, where interconnected permeable AlN shells developed on each AA6061 particle and imparted strength to the assembly. The resulting intershell spaces form an open-pore structure. When such an open-pore structure is heated above the liquidus of the core, an open-closed pore transformation occurs, where the molten core in each shell spontaneously migrates to fill the open pores outside, leaving a closed pore inside each shell. Based on this finding, porous AA6061 with different open-pore fractions was fabricated by heating open-pore structures of AA6061 into the semisolid region, where the liquid fraction changes with temperature. The mechanism for the open-closed pore transformation is identified through detailed microstructural and thermodynamic analyses. Criteria for the open-closed pore transformation are specified. Additionally, net shape fabrication of porous aluminum with controlled pore features is realized using the novel concept.