Fabrication of foamable precursors by powder compression and induction heating process
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9/26/04
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Fabrication of Foamable Precursors by Powder Compression and Induction Heating Process S.W. YOUN and C.G. KANG In the powder compact melting technique, metallic foams are fabricated by heating a precursor, thus initiating cell growth and foam formation. Proper precursor fabrication is very important because the density distribution after foaming and the foamability are determined during the precursor-fabrication process. The fabrication of the precursor has to be performed very carefully because any residual porosity or other defects will lead to poor results in further processing. In order to evaluate the effect of the compaction parameters on the kinetics of the foaming process, a series of experiments were performed. In this study, 6061 aluminum foams having a closed-cell structure were fabricated by the powder compact method and an induction heating process. An induction coil was designed to obtain a uniform temperature distribution over the entire cross-sectional area of the precursor. To establish the foamable precursor fabrication conditions, the effects of process parameters such as titanium hydride content (0.1 to 1.5 wt pct) and the compression pressure of the foamable precursor (50 to 150 kN) on the pore morphology were investigated.
I. INTRODUCTION
AL foams are ultra-lightweight porous Al alloys that have high stiffness at very low density, high impact energy absorption, heat and fire resistance, and greater thermal stability than any organic material.[1,2,3] The Al foams have been applied to parts such as automobile bumpers and crash boxes because they have a very high compressive strength and good energy absorption efficiency compared to polymer foam materials.[3–6] For the fabrication of complex threedimensional Al foam components such as automobile parts, the powder compact melting technique has been widely used,[7–10] in which metallic foams are fabricated by heating precursors, thus initiating pore growth and foam formation. In the powder compact melting technique, the precursor has to be prepared very carefully because the density distribution after foaming and the foamability are determined during the precursor fabrication process. Foaming agents greatly influenced density distribution and pore orientation of Al foams, which in turn influence the mechanical properties.[1,11] In addition, precursors of low density allow the escape of hydrogen, reducing the foam efficiency.[7] Therefore, it is very important to produce precursors of uniform density distribution and without any defects. In fabricating precursors, the important process parameters are the foaming agent contents, the compaction temperature, and the compaction pressure, among others. When Al foams are fabricated using TiH2 powder as the foaming agent, ranges of the preheat temperature and TiH2 content have been reported as 450 to 500 °C[7,12–14] and 0.6 to 1 wt pct[1,15] respectively. However, the proper compaction pressure during the compression process of the mixed powder has not yet been established. In
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