Static and dynamic energy absorption of Al foams produced by the sintering and dissolution process
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I. INTRODUCTION
AL foams have found increasing applications in many areas, including fortifying building and transport structures against buckling and impact, as heat exchangers, and as sound absorbers, owing to their exceptional properties.[1,2,3] The properties of an Al foam are primarily determined by the composition of the matrix material and the relative density as well as topology of the cells, which varies considerably for different manufacturing methods. The microstructure of the foam matrix is largely determined by the form of the Al in processing. While the foam made by a liquid-route method is generally free of impurities in the cell walls or struts, the foam made by a solid-route method may incorporate considerable amounts of oxides and other defects in the cell walls. The morphology of the cells of the foam is, however, mainly determined by the foaming agent used. The Al foams made by gas injections into the Al melt or decomposition of gas-releasing particles in the Al melt have soap-bubblelike polyhedral closed cells.[4] The Al foams made by casting the Al melt in an unleachable negative mold or by pressure infiltration of the Al melt into a leachable particle compact have open cells formed by a network of thin struts. The Al foams made by decomposition of gas-releasing particles in an Al powder compact have closed cells with relatively thick walls. The foams made by the sintering and dissolution process (SDP) have open cells with rough walls, a combination different from any of the aforementioned foams. The commercial foams currently available have shown a wide range of mechanical properties.[4] To evaluate the effectiveness of the Al foam for energy absorption under static and dynamic conditions, the manufacturing method and its conditions need to be taken into account. The SDP is a novel process for manufacturing Al foams, which was developed at the University of Liverpool.[5] The SDP consists of mixing, compacting, and sintering of Al D.X. SUN, Postgraduate Student, and Y.Y. ZHAO, Lecturer, are with the Department of Engineering, University of Liverpool, L69 3GH, Liverpool, United Kingdom. Contact e-mail: [email protected] Manuscript submitted April 23, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
and NaCl powder mixtures and final dissolution of the NaCl. It is a relatively low-cost process for manufacturing opencell Al foams because of the inexpensive raw materials and simple process equipment. The cell sizes and porosities of the Al foams made by the SDP can be controlled accurately by selecting appropriate NaCl particles and by specifying the proportions of Al and NaCl in the compacts, because the morphology and sizes of the cells are virtually replicas of those of the NaCl particles. The porosity of the foams is usually in the range of 50 to 85 pct. The microstructural and mechanical characteristics of the foams made by this route are considerably different from those made by the other commercial methods and need to be investigated. The mechanical properties and the energy-absorption prop
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