Papers by Author: Yeong Hwan Song

Abstract: Fabrication of Aluminum foam with near net shape has been investigated by powder metallurgy method and conventional pouring method. PM method is good for fabrication of near net shape foam, but it needs high cost compared with pouring method. More cost-effective methods are needed to make near net shape al foam to be applied various field. Therefore, novel method for fabrication Al foam was researched in this paper. In order to prepare near shape Al foams with homogeneous pore structures, the so-called upward foaming method was designed and applied. By using this method, two kinds of molds were designed, one is stainless mold used for melting and foaming Al and another is the plaster mold with near net shape. The fabrication procedures of near net shape Al foam are as following: (1) a quantity of Al ingot was melted in the stainless mold; (2) Ca particles was added in the Al melt to increase its viscosity; (3) TiH2 was introduced in the thickened Al melt to make melt being foamed; (4) the plaster mold was put on the stainless steel one to make enlarging Al melt foam fill with the plaster one; (4) the plaster mold was removed and was cooled. In this study, in order to get near net Al foam with relative good pore structures, the plaster molds were designed with three different upside styles and their effects on the pore structures (pore size, porosity and cell wall thickness) of Al foams were investigated. The results showed that the Al foam had the relative good pore structures when the plaster mold with a void was applied.

Abstract: Al-Mg alloy foams were synthesized via conventional melt foaming method. Ca and TiH2 were introduced into molten Al-Mg alloys with different magnesium contents. The macrostructures of resultant alloy foams were analyzed and correlated with compressive properties estimated by compression test. It is shown that the pore structures observed in alloy foams degraded with increasing Mg contents. This tendency was shown to be consistent with compressive characteristics of corresponding alloy foams. In detail, plateau strength was high for Al-1wt%Mg alloy foams, exhibiting a gradual decrease in plateau strength with increasing magnesium content.

Abstract: The influence of wheel speed and melt temperature on the surface characteristics of slag fibers were examined in mineral fibers synthesized from the steel-making slag, using a modified melt extraction method, i.e. melt spinning. The synthesized fibers were characterized by optical microscope and scanning electron microscopy. It was found that the wheel speed of 700 rpm generated better quality of mineral fibers in terms of diameter and length. This was attributed to the relative extent of contact width between the flowing melt and the rotating wheel. The thickness of the slag fibers were also decreased with increasing the slag melt temperature due mainly to significant decrease in the viscosity of the slag melt. In addition, the lower melt temperature caused an increase in number of shots plus the mineral fibers.

Abstract: Al-Mg alloy foams containing different Mg contents were synthesized via a conventional melt foaming method. The surface structures of pores formed in resultant foamed alloys was characterized by scanning electron microscopy and x-ray diffractometer. It was found that the pore structures were deteriorated with increasing Mg contents, while the percent porosities did not vary with increasing Mg contents, about 90% and 3~5 mm in pore size. The detailed microstructural examination conducted on increasing Mg containing alloy foams revealed presence of various oxide particles on the surface of individual cells, including MgAl2O4 particles in a form of fine spinel; its small amount for Al-1wt%Mg alloy foam but relative high amount of Al-4wt%Mg one. This suggested the negative effect of MgAl2O4 on the stable pore and thus cell structures in corresponding alloy foams. The possible mechanism associated with MgAl2O4 formation was discussed in the present study.

Abstract: Metal foams are not easy to use as materials as their manufacturing process involves all three, solid, liquid and gaseous phases occurring simultaneously at varying temperatures and moreever the morphology of the solidified foam is quite complex. There has not been any report on the stabilization of metal foams. To compare the stabilisation of metal foams using a different method, powder metallurgy and casting method using SiC and Ca alloy particle are required. Our investigation results showed deeply etched valleys with high oxygen content and secondary phases attached to line-shaped pores with higher SiC content than the matrix. These line-shaped pores - most probably oxide bifilms-form networks decorated with either secondary phases or oxide particle. We suspect that these decorated bifilms play a crucial role in the stabilisation of metal foams.