Fabrication of Two-Layered Aluminum Foam Having Layers with Closed-Cell and Open-Cell Pores
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ightweight aluminum (Al) foam has good energy absorption properties. In addition, Al foam with closed-cell pores has good thermal insulation properties, while Al foam with open-cell pores has good heat release properties since air or cooling water can flow through the pores. Therefore, it is expected to be used for vehicle components and as construction materials and heat-sink materials.[1,2] There are several investigations related to functionally graded (FG) Al foams, which consist of multiple layers of Al foam exhibiting different compression properties. In these investigations, FG Al foams with closed-cell pores[3–5] and open-cell pores[6,7] by varying the porosity, and with closed-cell pores[8,9] and open-cell pores[10] by varying the type of alloy were realized. In these studies, the precursor foaming process, in which heat treatment is conducted for foaming of solid Al containing blowing agent,[11,12] was used to fabricate the FG Al
YOSHIHIKO HANGAI, HIROKI IKEDA, KENJI AMAGAI, RYOSUKE SUZUKI, and MASAAKI MATSUBARA are with the Faculty of Science and Technology, Gunma University, Kiryu 3768515, Japan. Contact e-mail: [email protected] NOBUHIRO YOSHIKAWA is with the Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan. Manuscript submitted October 3, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
foams with closed-cell pores, while the sintering dissolution process[13,14] was used to fabricate those with open-cell pores. In this study, two-layered Al foam with both closed-cell and open-cell Al foam layers having similar compression properties was fabricated. This Al foam is expected to have a region with superior thermal insulation by closed-cell pores and a region with superior heat release properties by open-cell pores. The pore structures of the obtained Al foam were observed by X-ray computed tomography (X-ray CT). A compression test was conducted to observe the deformation behavior and to obtain the stress–strain curve of the Al foam. Figure 1 shows the fabrication process of the two-layered Al foam. As shown in Figure 1(a), AC4CH Al-Si-Mg alloy powder (average particle diameter of approximately 25 lm), titanium (II) hydride powder (TiH2, particle diameter under 45 lm) as a blowing agent, and a-alumina powder (Al2O3, particle diameter of approximately 1 lm) as a stabilization agent were prepared. As shown in Figure 1(b), they were thoroughly mixed, with TiH2 and Al2O3 mass fractions of 1 and 5 pct, respectively, corresponding to the mass of the AC4CH powder (Mixture I). The amounts of TiH2 and Al2O3 were determined in accordance with a previous study on the fabrication of Al foam by the precursor foaming process.[15] Similarly, pure Al powder (average particle diameter of approximately 20 lm) and sodium chloride (NaCl) powder (particle diameter ranging from 300 to 425 lm) were thoroughly mixed, with a NaCl volume fraction of 80 pct (Mixture II). As shown in Figure 1(c), Mixture II was placed in the graphite die, then Mixture I was placed in the die on top of Mixture II. Nex
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