Fabrication of Porous Aluminum with Directional Pores through Continuous Casting Technique
- PDF / 1,259,491 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 10 Downloads / 177 Views
N
ALUMINUM, magnesium, and their alloys are widely used as lightweight materials in various industrial applications. In particular, magnesium has attracted much attention because it is the lightest practical metal. However, magnesium exhibits inferior plastic processing and anti-corrosive behavior compared to aluminum. To compensate for the demerits inherent to both metals, production of porous aluminum is desirable. The strength of conventional porous aluminum with isotropic spherical pores is quite low due to the stress concentration occurring around the pores and the poor mechanical strength limits the applications of conventional porous aluminum.[1] On the other hand, porous metals with slender cylindrical pores aligned in one direction (lotus-type[2] (hereafter lotus metals) and gasar[3] porous metals) do not significantly contribute to stress in the slender pore growth direction. Consequently, the mechanical strengths of lotus and gasar metals are higher than those of conventional porous metals. Therefore, lotus aluminum possessing slender directional pores aligned in one direction is one of the most promising candidates for lightweight structural materials.[4] Numerous investigations have focused on the fabrication of porous aluminum and its alloys with slender directional pores formed by unidirectional T. IDE, Assistant Professor, and H. NAKAJIMA, Professor, are with The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan. Contact e-mail nakajima@ sanken.osaka-u.ac.jp Y. IIO, Graduate Student, formerly with The Institute of Scientific and Industrial Research, Osaka University, is now with the New Nippon Steel Company, Ltd., Kimitsu, Chiba 299-1141, Japan. Manuscript submitted January 31, 2012. Article published online August 14, 2012 5140—VOLUME 43A, DECEMBER 2012
solidification in a hydrogen atmosphere. Particularly, solidification defects have been emphasized for basic and applied research of a lightweight material. Table I is a compilation of these works.[5–15] Although aluminum alloys have high porosities, especially alloys with Si[15] and Fe,[12] none of the previous works produced porous aluminum with directional pores and a high porosity; the porosity is limited to 5 pct at most. Lotus aluminum can be fabricated utilizing the hydrogen solubility gap between a liquid and solid at the melting point in the unidirectional solidification process in a hydrogen atmosphere. When the melt dissolving hydrogen is solidified, the insoluble hydrogen is precipitated to evolve directional pores in the solidified region at the solid/liquid interface. Therefore, the following conditions are critical to fabricate highly porous lotus metals. (1) The hydrogen concentration dissolved in the molten metal should exceed several at. pct. (2) The metal should hold a smaller solid solubility of hydrogen so that the solubility gap between liquid and solid metals becomes larger. The system of hydrogen with copper, magnesium, and several transition metals such as iron, nickel, cobalt, and chr
Data Loading...
