Porous Metals and Metallic Foams

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Authors: Jörg Hohlfeld, Thomas Hipke, Friedrich Schuller
Abstract: The manufacturing processes for sandwiches made with aluminum or steel sheets are differentiated by their various melting ranges. Sandwiches with aluminum face sheets have recently been produced using to the so-called AFS technology, which includes a rolling process. However, if it is desirable to avoid rolling to reduce costs and allow for quick and flexible responses to the needs of the customer, the manufacturing process must be redesigned.
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Authors: Akram Salehi, Ahmad Moloodi, Faezeh Barzegar, Jalal Mirabbasi
Abstract: The relationship between temperature of sintering in neutral atmosphere and compression strength has been investigated for nickel foams produced by electrodeposition on an organic foam. The as-plated nickel foams are sintered at 600and 1000 in order to eliminate polyurethane and enhance ductility. The results show that the compression strength is significantly influenced by sintering temperature. The most ductile sample is gained by sintering at 600. In addition, samples sintered at this temperature have the higher energy absorbing capability. EDX analyses show that oxygen element raised from oxidation in high temperature presents in specimen sintered at 1000. Hollow struts are obvious in SEM image of treated foams. Keywords: Nickel foam, electrodeposition, EDX, Compression test
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Authors: Ahmad Moloodi, Mohammad Reza Moradi
Abstract: In this work the Aluminum-LECA composite foam was fabricated using the molten method. First, the LECA pellets were sieved in to three different sizes. The sieved LECA was placed on a regular and irregular form in to the mold cavity and then the molten aluminum was poured. The effect of LECA pellets as like as using vacuum system on filling the mold were also studied. Optical microscopy and scanning electron microscopy were used to study the pour morphology and the bonding of LECA and aluminum. The results show that using vacuum system can improve the fluidity of molten aluminum as like as the bounding with the LECA pellet and the aluminum matrix. It is also illustrated that with increase in the pellet size, the fluidity was increased. It was while that the orientation of LECA pellets has a significant influence on the fluidity. Keywords: Aluminum-LECA composite, fluidity, Vacuum system
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Authors: Hua Qiao Dong, Jun Liang, Fu Yang Li, Cheng Chuan Zhang, Song Bao Wang, Zuo Sheng Lei
Abstract: Previous researchers have proved that units constituting monodisperse bilayer foams can transform reversibly by changing foam liquid fraction. Structural transformation of bilayer ferro-foams caused by magnetic field is investigated in this paper. It is observed that bilayer ferro-foams transform from Tóth structure to honeycomb structure caused by liquid fraction change which attributes to foam imbibition under a uniform magnetic gradient field. In order to acquire critical structural transformation liquid fraction range, foam liquid fractions are calculated by image analysis. However, we also observed that, when applying a homogeneous magnetic field, bilayer ferro-foams can also perform this transformation at a constant liquid fraction. This phenomenon is related to energy absorption of foam system, which is induced by magnetic interaction of magnetic moments after applying a magnetic field. This self-organizational behavior of foam structure is believed to be based on energy minimization principle. This study opens possible applications in the field of metal foam preparation.
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Authors: Hui Meng Wang, Ming Zhou Su, Chang Chen
Abstract: Steel foams have been receiving a growing interest due to the unique structural properties. The space holder technique provides a high degree of freedom and allows to produce this kind of materials varying in a wide range of porosity. However, the accurate prediction of final porosities has been a difficult problem in this technique. Therefore, a nonlinear equation between spacer content (φ1) and porosity (P) of the sintered steel foams was established in this study when macropores, micropores and their volumetric change were taken into account at the same time, that was P = (aφ1+b)/(cφ1+d). Then, validation of the theoretical relationship was carried out using the experimental data by authors and other researchers. The results showed that the porosity could be well predicted by the nonlinear relationship with varied preparing parameters. One set of coefficients in the model equation, i.e., a, b, c, d, corresponds to a certain preparing condition, while these values changed in different preparing conditions.
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Authors: Chao Qun Guo, Ya Dong Sun, Yun Zhou, Bo Xie, Tian Yao Wang, Xiao Qing Zuo
Abstract: Copper foams by using CaCl2 as space holder were successfully manufactured by sintering and dissolution process. The porosity ranges from 75% to 91%, and cell size from 0.3mm to 3.0m. The volume fraction of CaCl2 and sintering temperature are the main factors that affect porosity of copper foam. The yield plateau stress of copper foams with porosity between 75.88% and 90.19% is in range of 12.1~1.2MPa. The yield plateau stress decreases with the increase of porosity. The energy absorption per unit volume (W) copper foams with porosity between 75.88% and 90.19% is in range of 6.17~0.63MJ/m3. Under the condition of identical porosity, the absorption energy per unit volume (W) of copper foam is about 43% higher than aluminum foam. The maximum ideal energy absorption efficiency of copper foam is about 0.74, it indicates that the copper foam can be used as a good absorbing material.
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Authors: Hideo Nakajima, Takuya Ide
Abstract: Porous metals with long cylindrical pores aligned in one direction are fabricated by unidirectional solidification through pressurized gas method (PGM) and thermal decomposition method of gas compounds (TDM). The pores are evolved from insoluble gas when the molten metal dissolving the gas is solidified in the dissolving gas (PGM) or inert gas (TDM). Three fabrication techniques, mold casting, continuous zone melting and continuous casting techniques, are adopted. The latter two techniques can control the solidification velocity and the last one possesses a merit for mass production of lotus metals. The porosity, pore diameter and its length are able to be controlled by the solidification velocity and ambient gas pressure, while the pore direction can be controlled by the solidification direction. Anisotropy in the elastic and mechanical properties is resulted from anisotropic pore morphology. The anisotropic behaviors of tensile, compressive and fatigue strength are explained in terms of the dependence of stress concentration on the pore orientation. The anisotropic properties of thermal, electrical conduction and magnetization are also found, which are attributed to the scattering of heat flux, electric current and magnetic flux with anisotropic pores, respectively. Several applications of the porous metals to manufacturing products are investigated. The unidirectional pores can be utilized for high performance of heat sinks for electronic devices of cars and computers. Thus, the porous metals are expected to be used for various manufacturing products.
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Authors: Yong Zhang, Zong Min Chen, Zhao Jun Wang, Jing Hui Liu
Abstract: Three kinds of aluminum foam of different pore sizes were prepared with a tailor-made low-pressure infiltration device. CaO granules in three sizes (0.45~0.71mm,0.71~090mm and 1.25~1.60mm) were selected as infiltrating agents. The processing parameters were as follows: granules preheat temperature of 700 °C,infiltration pressure of 0.04 MPa and aluminum liquid temperature of 720 °C. In order to improve the removal performance and porosity, mixture of CaO powder of finer than 300 mesh and pure alcohol was mixed uniformly with granules, which made the slurry-coating granules conformal contacts rather than point contacts as in the traditional infiltration method. The testing results show that among all aluminum foam specimens tested with transfer function methods, two kinds have high sound absorption coefficient in low frequency (250~1600Hz).
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Authors: Xiao Long Liang, Hong Jie Luo, Xiao Tao Ma, Zhi Gang Zhang, Jian Rong Xu
Abstract: Lead-foam is a type material holding high porosity and specific surface area and can be used as grid material of storage battery and anode material in zinc electrolysis. Based on the infiltration casting system designed according to Pascal's and pressure infiltration principle, lead-foam with porosity 58-61%, cell diameter 1.18-3.35mm was successfully manufactured via infiltration casting method where industrial sodium chloride (NaCl) particles were used as porogens. As preparation of preform is a key step in infiltration casting process, orthogonal tests were performed to study the some process parameters’ effects on the porosity of the preform and the orthogonal test results revealed that the rank from high to low of the parameters’ effects on the porosity of preform was porogen size, cold-compacting pressure, sintering time and sintering temperature.
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