Fabrication of Lotus-Type Porous Al-Si Alloys Using the Continuous Casting Technique

Abstract

Lotus-type porous 8,12,14, and 18 wt pct) alloys were fabricated using the continuous casting technique under a hydrogen gas pressure of 0.1 MPa at various transference velocities, and the effects of the silicon content level and transference velocity on the pore morphology and porosity were investigated. Both the porosity and the average pore diameter increase as the silicon content level increases and decrease as the transference velocity increases. In particular, the velocity dependence is obviously exhibited at a silicon content level higher than 12 wt pct. The pore shape is changed from irregular in the higher-dendrite fraction to nearly circular in the lower-dendrite fraction. The porosity and the pore morphology are influenced by the silicon content level and transference velocity. In the model, these results can be understood with the explanation that the pores, which contribute to the increase in porosity, are generated at the eutectic fronts. This indicated that the porosity and the pore size in lotus-type porous Al-Si alloys can be well controlled by varying the silicon content level and the transference velocity.

Effect of Conditions of Unidirectional Solidification on Microstructure and Pore Morphology of Al-Mg-Si Alloys

“…The growth of pores is interrupted by the surrounding primary -dendrites, when the volume fraction of eutectic phase is small according to the results of fabrication of lotus-type porous Al-Si alloys. 7) In Al-4 mass% Si and Al-8 mass% Si with a small volume fraction of eutectic phases, the morphologies and direction of pores were influenced by the surrounding primary -dendrites. On the other hand, in Al-Si alloys with a Si-content of 12, 14, and 18 mass% with a large volume fraction of eutectic phases, the pores grew in the solidification direction and were in a cylindrical shape.…”

“…5,6) The thermal decomposition method was developed by Nakajima and Ide in order to fabricate lotus-type porous metals without explosive gas and high pressure chamber. 5) Until now several kinds of lotus aluminum alloys have already been fabricated with hypo-eutectic Al-Si alloys 7) and hypo-eutectic Al-Cu alloy 8) by continuous casting technique in hydrogen atmosphere of 0.1 MPa. These results showed that pores were formed in the eutectic region among several primary -dendrites by the solubility gap of hydrogen between liquid and solid phases, and then grew in the direction of growth of the columnar primary -dendrites.…”

Fabrication of Porous Aluminum with Directional Pores through Continuous Casting Technique

“…Table I is a compilation of these works. [5][6][7][8][9][10][11][12][13][14][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.…”

“…Thus, to increase porosity and to clarify the pore formation mechanism in lotus aluminum, it is reasonable to consider the competitive growth between directional pores and solid metal because the hydrogen flux is related to the solidification conditions. Several experimental investigations have examined the effects of partial pressure and solidification velocity on the porosity and pore size in metals (copper, [15,21] stainless steel, [22] and magnesium [23] ) to evaluate the porosity and pore size from the solidification processing parameters. On the other hand, pore growth in lotus metals has been theoretically evaluated from the viewpoint of competitive growth between directional pores and solid metal.…”

“…In particular, the [9] Al-16 pct Si 0.1 (?) 100À200 1.5À7.2 Shinada (1983) [10] Al-(10À20) pct Cu H 2 + Ar mixture 200À400 <1.3 Lee (1997) [11] Al- (1,8) pct Fe H 2 9À17 Bonenberger (1998) [12] A357 0.3À1.5 <12 Paradies (1998) [13] AA2090 [14] Al-(4À18) pct Si 0.1 <2000 3À40 Park (2009) [15] present work clarifies that the porosity and the pore size are affected significantly by the solidification velocity, which is decreased by one to two orders of magnitude compared to those for copper, magnesium, and transition metals. Based on this knowledge, lotus aluminum with a porosity as high as 40 pct is obtained for the first time.…”