Bubble Formation at a Submerged Orifice in High-Speed Horizontal Oscillation
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CLOSED-CELL aluminum foams have been getting more and more extensive application because of their high specific strength and good energy absorption performance.[1] Aluminum foams fabricated by gas injection route, by blowing air directly into the molten aluminum alloy containing a certain amount of ceramic particles, have the advantages of simple process and low costs compared to foams produced by other preparation methods. The preparation of aluminum foams with small-sized bubbles is a hot topic at present. The smaller bubble has a smaller liquid film area, which is conducive to the film stability.[2] Aluminum foam with smaller cell size has a more spherical pore structure,[3] and the big cavities and structural defects on cell walls can be reduced accordingly,[4] so the reducing of the cell size of NINGZHENWANG and GUIQUANWANG, Ph.D. Candidates, are with the Department of Materials Engineering, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 China. XIANG CHEN, HUAWEI ZHANG, and YUAN LIU, Vice Professors, and YANXIANG LI, Professor, are with the Department of Materials Engineering, School of Materials Science and Engineering, Tsinghua University, and also with the Key Laboratory for Advanced Materials Processing Technology (MOE), Tsinghua University, Beijing 100084, China. Contact e-mail: [email protected] JIANYU YUAN, Engineer, is with the Department of Materials Engineering, School of Materials Science and Engineering, Tsinghua University, and also with the Aerospace Research Institute of Materials & Processing Technology, Beijing 100076, China. Manuscript submitted April 22, 2016. Article published online August 17, 2016. 3362—VOLUME 47B, DECEMBER 2016
aluminum foams can improve the mechanical properties.[5] Moreover, small-sized bubbles was more stable, so it has a great potential to take thermoforming on the aluminum foams with small cell size, such as die casting and welding.[6,7] By the optimal design of orifice[8,9]or adjustment of processing parameters,[10] the bubble size in liquid could be reduced. However, these methods in the static foaming route still have limitation to decrease the bubble size. The experimental and calculated results in aqueous foam have shown that the bubble size decreases about 50 pct with the increase of water velocity in the range of 1 to 3 m/s.[11] Therefore, further reducing of bubble size should be achieved through the shearing and dispersing effects from external forces. In the 1990s, Alcan and Norsk Hydro developed the dynamic gas injection route to inject air with a rotating or reciprocating gas injector, and to disperse the injected air by this motion,[12–14] and the cell size of aluminums foams produced by this method is not uniform due to the disturbance of the melt caused by the gas injector. This also causes nonuniformity in the cell size distribution of the aluminum foams.[15–17] Babcsa´n[18] took advantage of ultrasonic wave to disperse the ultrafine particles and ultrasonic oscillation to act on the interaction region between molten
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