Evaluation of porosity in lotus-type porous magnesium fabricated by metal/gas eutectic unidirectional solidification

Lotus-type porous magnesium with elongated pores has been fabricated by a metal/gas eutectic unidirectional solidification method (Gasar process) under a pressurized hydrogen and argon gas mixture. Through solving the steady-state solute distribution function before the solidification front, a theoretical model was developed to calculate the hydrogen content in the solid metal and then a new theoretical relation was attained to predict porosity. The porosity is significantly affected by the partial pressures of hydrogen and argon. The calculated values are in good agreement with the experimental results. Additionally, the pressure condition for the formation of the lotus-type porous structure was also investigated through analyzing the solute concentration condition for the growth of a gas bubble.