Fabrication of lotus-type porous Mg-Mn alloys by metal/gas eutectic unidirectional solidification

Lotus-type porous Mg-xMn (x=0, 1, 2 and 3 wt.%) alloys were fabricated by metal/gas eutectic unidirectional solidification (the Gasar process). The effects of Mn addition and the fabrication process on the porosity, pore diameter and microstructure of the porous Mg-Mn alloy were investigated. Mn addition improved the Mn precipitates and increased the porosity and pore diameter. With increasing hydrogen pressure from 0.1 to 0.6 MPa, the overall porosity of the Mg-2wt.%Mn ingot decreased from 55.3% to 38.4%, and the average pore diameter also decreased from 2465 to 312 mu m. Based on a theoretical model of the change in the porosity with the hydrogen pressure, the calculated results were in good agreement with the experimental results. It is shown that this technique is a promising method to fabricate Gasar Mg-Mn alloys with uniform and controllable pore structure.