Friction Powder Compaction for Fabrication of Open-Cell Aluminum Foam by the Sintering and Dissolution Process Route
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luminum (Al) foam is a lightweight and highly functional material.[1] Open-cell Al foam can be used for a wide range of applications where heat exchange, sound absorption, and filtration are required. Zhao and Sun[2] developed the sintering and dissolution process (SDP) route on the basis of powder metallurgy for fabricating open-cell Al foam. In this process, a mixture of Al powders and soluble powders, such as sodium chloride (NaCl),[2–10] carbamide,[11,12] and crystalline raw cane sugar,[13,14] are compacted and sintered by applying appropriate pressure and heat using an electric furnace or by spark plasma sintering. Then, the sintered mixture is placed in water to remove the soluble particles and open-cell Al foam can be obtained. In some cases, the sintering is conducted after the removal when the soluble particles have a low melting temperature.[11–14] The SDP route has many advantages. First, the pore structure (porosity, pore size, and pore morphology) can be easily and accurately controlled by adjusting the proportion of Al/soluble powders and selecting the appropriate soluble powders. Second, a thin foam sheet of approximately 1-mm thickness can be obtained using soluble particles of several hundred micron size.[8] Third, YOSHIHIKO HANGAI, Associate Professor, and HIROAKI YOSHIDA, Graduate Student, are with the Graduate School of Engineering, Gunma University, Kiryu 376-8515, Japan. Contact e-mail: [email protected] NOBUHIRO YOSHIKAWA, Professor, is with the Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan. Manuscript submitted September 30, 2011. Article published online January 19, 2012 802—VOLUME 43A, MARCH 2012
the soluble powders in the sintered mixture can be easily removed just by placing the sintered mixture in water at room temperature, that is, SDP is a simple process and, essentially, no heat source is necessary for the removal of the soluble particles. In this study, a new friction powder compaction (FPC) process by the SDP route for fabricating opencell Al foam, which requires no external heat sources for compacting, sintering, and removal, is demonstrated. The compacting and sintering of the powder mixture are conducted only by a rotating tool plunged into the mixture. Namely, the compacting and sintering of the mixture is achieved because of the friction heat, pressing load, and intense plastic deformation generated by the rotating tool plunged into the mixture. In this article, we aim to investigate the pore structure and compressive response of the obtained Al foam. In addition, the sintered mixture during the removal process was observed nondestructively by X-ray CT to reveal the progress of the removal of soluble particles and to confirm that they were completely dissolved. Figure 1 shows a schematic of the FPC process. First, commercially available as-received Al (99.9 pct purity, average diameter of 20 lm) and NaCl (99.9 pct purity, diameter range approximately from 180 lm to 600 lm) powders were thoroughly mixed at a specific weight ratio to obtain Al fo
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