Papers by Author: Soo Han Park

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: The surface tension and the viscosity characteristics of molten metal are the most important factors in casting process and metallic foam manufacturing especially. The surface tension (by the modified ring method) and the viscosity (by the rotational method) of molten Al-Cu alloys have been measured under high purity Ar gas atmosphere. The surface tension and the viscosity of Al-Cu alloys were investigated in the temperature range of 660-800oC, and the effects of the additional elements were investigated at the 660~680
. The result show that the surface tension and viscosity of these alloys decrease with increasing temperature together. The viscosity of Al-Cu alloys near the melting point is about 4.7 to 5.7 [mPa.s]. The effect of additional thickening elements has the tendency that is the surface tension decreased and the viscosity increased. This anomalous behavior has the relation of the preferential adsorption of high activity elements on the surface.

Abstract: Foamed metal is a kind of porous material with pores in the metal matrix. One of the possible process routes is to blow gas bubbles into liquid metals. However, many metallic foams produced by this foaming method have coarse and irregular cell structures. The industrial aim is to fabricate foams with more uniform structure and cell size. It is important to understand the mechanisms and factors controlling. The rheological characteristics are the most important factors in the metal foam manufacturing. Thus this study investigated the bubble behavior of the molten metal and its two most important two parameters: surface tension and liquid viscosity. The surface tension (by the ring method) and the viscosity (by the rotation method) of Mg-Al alloy (AZ91, AM60) have been measured under pure Ar and SF6 + CO2 atmosphere. The results show that the surface tension and the viscosity of these alloys decrease with increasing temperature. The addition of Ca and SiC to Mg alloys decreases the surface tension and increases the viscosity. This anomalous behavior is related with the preferential adsorption of high activity elements on the surface.

Abstract: Aluminum foam with 0.2 g/cm3 density showed a good sound absorption property at frequencies higher than 2000 Hz. Compressed aluminum foam with an air gap of 50 mm or higher exhibited a very high sound absorption property near 400 Hz.

Abstract: Metal foam was produced by the Melt Foaming Method. In this foaming process, the surface tension and the viscosity of molten Al (recycled waste Al) and Mg alloy (Az91) that were measured respectively by the ring method and the rotational method are the most important two factors. They surface tension and the viscosity were investigated in the temperature range of about 600-900°C and the effects of the additional surface-active elements were investigated at the about 640°C. The measured surface tension of the molten recycled Al and Az91 decreased linearly with the increasing temperature of Ar gas (99.999%) and SF6+CO2 (1:100) atmosphere. The effect of surface-active elements is a decrease of the surface tension and an increase of the viscosity. The optimal conditions for the foam metal manufacturing are needed the low surface tension and the high viscosity. It is possible that the optimal conditions of the surface tension and the viscosity can be obtained through controlling the amount of adding surface-active elements.