Effect of the Amount of Gases on the Foaming Efficiency of Porous Aluminum Using Die Castings Fabricated by Friction Sti
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ell porous aluminum is a lightweight material with good energy absorption and sound insulation properties. Therefore, it is expected to be used for the manufacture of lightweight components and for improved crash energy absorption in automobiles.[1] The precursor method is often used for fabricating closedcell porous aluminum.[2–6] In this method, a foamable precursor, which consists of a blowing agent powder distributed uniformly in a solid-state aluminum alloy, is fabricated first. By heat treating the precursor, gases generated by the decomposition of the blowing agent expand the aluminum alloy and porous aluminum is fabricated. Recently, we have developed a new processing route using friction stir processing (FSP) to fabricate the precursor, which uses aluminum alloy high-pressure die castings without the use of a blowing agent.[7] The die castings generally contain a significant amount of gas pores.[8,9] Consequently, die castings can be used as an alternative precursor of porous aluminum to blowing agent powder, which is expensive and an explosion hazard. Also, the die castings are produced by a highYOSHIHIKO HANGAI, Assistant Professor, and HIROKI KATO, Graduate Student, are with the Department of Mechanical System Engineering, Gunma University, Kiryuu 376-8515, Japan. Contact e-mail: [email protected] TAKAO UTSUNOMIYA, Professor, is with the Research Organization for Advanced Engineering, Shibaura Institute of Technology, Saitama 337-8570, Japan. SOICHIRO KITAHARA, Chief Executive, is with Gundai Co., Ltd., Isesaki 372-0854, Japan. Manuscript submitted February 25, 2010. Article published online June 5, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
productivity manufacturing process with high recyclability. Therefore, this new processing route is expected to reduce the cost of manufacturing porous aluminum. However, gases and microstructures such as Si and intermetallic particles, which are expected to act as the nuclei of pores, may be segregated in the die castings. They must be distributed uniformly, because the pores in porous aluminum are required to have a uniform morphology and distribution. FSP has been used for refining and dispersing uniformly the microstructure of aluminum alloy castings,[10–12] as well as for fabricating metal matrix composites with uniformly dispersed ceramic particles.[13–15] Therefore, it is expected that FSP can disperse uniformly the gases, the nuclei of pores, and the stabilization agent powder added to the precursor in aluminum alloy die castings. In this study, various types of aluminum alloy die castings containing various amounts of gases were fabricated. The effect of the amount of gases on the foaming efficiency (porosity) of the porous aluminum by using FSP was investigated. Figure 1 shows a schematic illustration of the manufacturing process of the precursor carried out in this study. In the experiments, Al-Si-Cu aluminum alloy ADC12 (equivalent to A383.0 aluminum alloy) diecasting plates of 3 mm thickness, 70 mm width, and 130 mm length were used. Table I shows the
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