Fabrication of Gasar Porous Mg-Ag Alloys by Metal-Gas Eutectic Directional Solidification Method

Gasar porous Mg-Ag alloys exhibit competitive potential as biomaterials and as precursors for catalytic materials; their practical performances mainly depend on the pore structure inner porous alloys. In this paper, Gasar porous Mg-xAg alloys (with Ag contents of 0.5, 8.32, and 17.57 atom %) corresponding to the single-phase, subeutectic, and eutectic composition were prepared by a metal-gas eutectic directional solidification method. The effects of the Ag content level on the solidification microstructure and the pore growth behavior were investigated. The porosities decrease as the silver content level increases. The pore shape is changed from regular in Mg99.5Ag0.5 to irregular in Mg91.68Ag8.32 and then regular again in Mg82.43Ag17.57. The integrity of the pores changed from good to poor in the order of Mg82.43Ag17.57, Mg99.5Ag0.5, and Mg91.68Ag8.32, which was closely related to the width of the corresponding mushy zone from narrow (0 of eutectic composition) to wide. The width of the mushy zone with different silver contents was quantified by combining finite element simulations, and the orientation of the solidification microstructure of each alloy was analyzed. The random orientation of a solidification microstructure will hinder the growth of pores and cut off the correlation between the growth direction of pores and the solidification direction.