Bubble size control during the gas injection foaming process in aluminum alloy melt
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Yanxiang Lia) and Xiang Chen School of Materials Science and Engineering, Tsinghua University, Beijing, China 100084; and Key Laboratory for Advanced Materials Processing Technology, MOE, Beijing, China 100084 (Received 27 October 2014; accepted 19 February 2015)
The influences of parameters on the bubble size in aluminum alloy melt during the gas injection foaming process were studied. The four parameters were the orifice diameter (0.4–3.0 mm), the orifice numbers (1 and 4), the gas chamber volume (11–800 cm3), and the gas flux (10–282 L/h). It was found that the bubble size decreased with the decrease of the orifice diameter and the gas chamber volume, and with the increase of the orifice number. The effect of gas flux showed a dual-stage at different gas fluxes: the “metastable large bubble stage” and the “stable bubbling stage”. A modified semiempirical formula and a concept of “effective gas chamber volume,” which is the nominal chamber volume divided by the effective orifice number, were proposed. The bubble size calculated by the modified formula with the effective gas chamber volume agreed well with the experimental data.
I. INTRODUCTION
Aluminum foam is a kind of porous metal, which has lots of cellular pores inside. According to Chen and Li1 and Banhart,2 besides low density, high specific strength, and high specific stiffness, the aluminum foam also has performances of sound absorption and crash energy absorption. The gas injection foaming process is an important method to produce the aluminum foam. Its product usually has big pores and high porosity, about 5–25 mm and 90 ; 98% according to Banhart.2 In this process, the gas containing oxygen is injected by a nozzle into the aluminum melt, which contains ceramic particles. According to Babcsán et al.,3 via adsorbing the particles and forming the oxide layers, the bubbles will not burst after floating on the melt surface and then form the foam. Kenny4 had proved that the performance of the aluminum foam was affected by the pore size. The pore size mainly depends on the size of the bubbles created by the nozzle. The nozzle has two types, dynamic type and static type. The dynamic nozzle creates bubbles by relative motion between the orifice and the melt.5 However, the static nozzle keeps still, and the bubble
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.71 J. Mater. Res., 2015
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size depends on the nozzle’s structure.6 In this study, the static nozzle was used. For a static nozzle, the parameters influencing the bubble size are the nozzle’s wettability, inner and outer diameters of the orifice, gas chamber volume, orifice number, gas flux, and so on. According to the reviews by Kulkarni and Joshi,7 and by Yang et al.,8 many researches have studied these factors. Recent researches mostly focus on the dynamic process of bubble formation by the numerical method. As a matter of fact, early researches, which got empirical or semiempi
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