Pore structure of porous Mg-1Mn-xZn alloy fabricated by metal–gas eutectic unidirectional solidification

Abstract Lotus-type porous Mg–1 wt.% Mn–xZn (x = 0 wt.%, 1 wt.% and 2 wt.%) alloys were fabricated by metal–gas eutectic unidirectional solidification (the Gasar method). Effects of Zn addition and the fabrication process on the porosity, pore diameter and microstructure of the porous Mg alloys were investigated. Zn addition from 0 wt.% to 1 wt.% and 2 wt.% to the Mg–1 wt.% Mn alloy decreased the porosity from 41.2% to 36.9% and 35.8%, respectively, with the same preparation processing. In the lotus-type porous Mg–1 wt.%Mn–1 wt.%Zn alloy, the porosities and average pore diameters changed with hydrogen pressures from 0.1 to 0.6 MPa. Conical areas that were rich in elemental Zn existed below the directional pores, and precipitates were also found in conical areas. Homogeneous directional pores existed in the lower portion of the ingot, and coarser directional pores and finer non-directional pores formed in the upper part. A theoretical model of the change in porosity with hydrogen pressure agreed well with the calculated porosities in the steady bubble growing area. The compressive strength of Mg-1 wt.Mn-Zn alloys can be increased by around 20 MPa through rising Zinc content from 1 wt.% to 2 wt.%, which basically linearly decline with the increasing of porosity. This work provides the basis for Gasar Mg–Zn–Mn alloy synthesis in biological applications and shows that the Gasar process is a promising method to fabricate Mg–Zn–Mn alloys with directional pores and a controllable pore structure.