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Gunma, Japan

Hangai Y.,Gunma University | Utsunomiya T.,Shibaura Institute of Technology | Kuwazuru O.,University of Fukui | Kitahara S.,Hokudai Co. | Yoshikawa N.,University of Tokyo
Materials | Year: 2015

Recently, to further improve the performance of aluminum foam, functionally graded (FG) aluminum foams, whose pore structure varies with their position, have been developed. In this study, three types of FG aluminum foam of aluminum alloy die casting ADC12 with combinations of two different amounts of added blowing agent titanium(II) hydride (TiH2) powder were fabricated by a friction stir welding (FSW) route precursor foaming method. The combinations of 1.0-0 mass %, 0.4-0 mass %, and 0.2-0 mass % TiH2 were selected as the amounts of TiH2 relative to the mass of the volume stirred by FSW. The static compression tests of the fabricated FG aluminum foams were carried out. The deformation and fracture of FG aluminum foams fundamentally started in the high-porosity (with TiH2 addition) layer and shifted to the low-porosity (without TiH2 addition) layer. The first and second plateau regions in the relationship between compressive stress and strain independently appeared with the occurrence of deformations and fractures in the high- and low-porosity layers. It was shown that FG aluminum foams, whose plateau region varies in steps by the combination of amounts of added TiH2 (i.e., the combination of pore structures), can be fabricated. © 2015 by the authors.

Hangai Y.,Gunma University | Saito M.,Gunma University | Utsunomiya T.,Shibaura Institute of Technology | Kitahara S.,Hokudai Co. | And 2 more authors.
Materials | Year: 2014

Aluminum foam has received considerable attention in various fields and is expected to be used as an engineering material owing to its high energy absorption properties and light weight. To improve the mechanical properties of aluminum foam, combining it with dense tubes, such as aluminum foam-filled tubes, was considered necessary. In this study, an aluminum foam-filled steel tube, which consisted of ADC12 aluminum foam and a thin-wall steel tube, was successfully fabricated by friction welding. It was shown that a diffusion bonding layer with a thickness of approximately 10 μm was formed, indicating that strong bonding between the aluminum foam and the steel tube was realized. By the X-ray computed tomography observation of pore structures, the fabrication of an aluminum foam-filled tube with almost uniform pore structures over the entire specimen was confirmed. In addition, it was confirmed that the aluminum foam-filled steel tube exhibited mechanical properties superior to those of the ADC12 aluminum foam and steel tube. This is considered to be attributed to the combination of the aluminum foam and steel tube, which particularly prevents the brittle fracture and collapse of the ADC12 foam by the steel tube, along with the strong metal bonding between the aluminum foam and the steel tube. © 2014 by the Authors.

Hangai Y.,Gunma University | Kamada H.,Gunma University | Utsunomiya T.,Shibaura Institute of Technology | Kitahara S.,Hokudai Co. | And 2 more authors.
Materials | Year: 2014

Al foam has been used in a wide range of applications owing to its light weight, high energy absorption and high sound insulation. One of the promising processes for fabricating Al foam involves the use of a foamable precursor. In this study, ADC12 Al foams with porosities of 67%-78% were fabricated from Al alloy die castings without using a blowing agent by the friction stir processing route. The pore structure and tensile properties of the ADC12 foams were investigated and compared with those of commercially available ALPORAS. From X-ray computed tomography (X-ray CT) observations of the pore structure of ADC12 foams, it was found that they have smaller pores with a narrower distribution than those in ALPORAS. Tensile tests on the ADC12 foams indicated that as their porosity increased, the tensile strength and tensile strain decreased, with strong relation between the porosity, tensile strength, and tensile strain. ADC12 foams exhibited brittle fracture, whereas ALPORAS exhibited ductile fracture, which is due to the nature of the Al alloy used as the base material of the foams. By image-based finite element (FE) analysis using X-ray CT images corresponding to the tensile tests on ADC12 foams, it was shown that the fracture path of ADC12 foams observed in tensile tests and the regions of high stress obtained from FE analysis correspond to each other. Therefore, it is considered that the fracture behavior of ADC12 foams in relation to their pore structure distribution can be investigated by image-based FE analysis. © 2014 by the authors.

Hangai Y.,Gunma University | Nakano Y.,Gunma University | Koyama S.,Gunma University | Kuwazuru O.,University of Fukui | And 2 more authors.
Materials | Year: 2015

Aluminum foam is usually used as the core of composite materials by combining it with dense materials, such as in Al foam core sandwich panels and Al-foam-filled tubes, owing to its low tensile and bending strengths. In this study, all-Al foam-filled tubes consisting of ADC12 Al-Si-Cu die-cast aluminum alloy foam and a dense A1050 commercially pure Al tube with metal bonding were fabricated by friction welding. First, it was found that the ADC12 precursor was firmly bonded throughout the inner wall of the A1050 tube without a gap between the precursor and the tube by friction welding. No deformation of the tube or foaming of the precursor was observed during the friction welding. Next, it was shown that by heat treatment of an ADC12-precursor-bonded A1050 tube, gases generated by the decomposition of the blowing agent expand the softened ADC12 to produce the ADC12 foam interior of the dense A1050 tube. A holding time during the foaming process of approximately tH = 8.5 min with a holding temperature of 948 K was found to be suitable for obtaining a sound ADC12-foam-filled A1050 tube with sufficient foaming, almost uniform pore structures over the entire specimen, and no deformation and minimum reduction in the thickness of the tube. © 2015 by the authors.

Saito K.,Gunma University | Hangai Y.,Gunma University | Utsunomiya T.,Shibaura Institute of Technology | Kuwazuru O.,University of Fukui | And 2 more authors.
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals | Year: 2013

Aluminum foam is a multifunctional material with a light weight and a high energy absorption. In this study, an A1050 (pure Al)-A6061(A1-Mg-Si)-ADC12(A1- Si-Cu) aluminum alloy three-layered-structure functionally graded (FG) aluminum foam was fabricated by the friction stir welding (FSW) route. The pore structures and elemental Cu content of the fabricated A1050-A6061-ADC12 FG aluminum foam were observed nondestructively by X-ray CT inspection and Electron Probe Microanalysis (EPMA), respectively. It was shown that three-layered A1050-A6061-ADC12 FG aluminum foam can be fabricated with different pore structures and elemental Cu contents in each layer. The compression properties and deformation behavior of the A1050-A6061-ADC12 FG aluminum foam were obtained by a compression test. It was shown that the fabricated A1050-A6061-ADC12 FG aluminum foam exhibited three different deformation stages and three plateau regions corresponding to the pore structures and types of aluminum alloy in each layer. © 2013 The Japan Institute of Metals and Materials.

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