Fabrication of Lotus-Type Porous Aluminum Utilizing Decomposition of Moisture

Abstract

Lotus-type porous aluminum with cylindrical pores oriented in one direction was fabricated by a casting method utilizing the decomposition of moisture in a vacuum. Hydrogen decomposed from moisture is utilized for cylindrical pores to grow during unidirectional solidification. However, pores are not formed in the case of a casting in hydrogen or argon atmosphere, because hydrogen or argon gas pressure suppresses the pore growth. The porosity of lotus aluminum does not depend on the moisture amount, which indicates that the moisture amount is almost saturated within the amount used in this study. The average pore diameter does not depend on the moisture amount, because the pore diameter depends mainly on ambient pressure and solidification rate. The distribution of pores becomes homogeneous by decreasing melting temperature, because the rate of the reaction of moisture possibly becomes low (more suitable for pore growth) by decreasing the melting temperature.

Effect of the Amount of Gases on the Foaming Efficiency of Porous Aluminum Using Die Castings Fabricated by Friction Stir Processing

“…[16] The efficiency of each gas in expanding the aluminum alloy was unclear in this study, i.e., it was unclear whether equal amounts of N 2 and H 2 in the die castings have the same expansion efficiency and can fabricate porous aluminum with the same porosity. However, many types of gases such as H 2 , [2][3][4][5][6][17][18][19][20] N 2 , [18] and CO 2 or CO [19,[21][22][23][24] have been used for fabricating porous metals. It is considered that the total amount of gas dominates the expansion efficiency.…”