Papers by Author: Koichi Kitazono

Abstract: Closed-cell Zn-22Al superplastic alloy foams were manufactured through the melt foaming process. The Zn-22Al foams were produced with varying porosity of 51-71%. The tensile and compressive properties of the Zn-22Al foams were investigated at 523 K. The compressive specimen has m-value of 0.55 in the low strain rate region. This is because of the superplastic deformation induced by the fine microstructure of the cell wall. Though the superplastic elongation was not obtained in high temperature tensile test, the elongation was higher than that of conventional aluminum foams.

Abstract: Plastic deformation of magnesium alloy is limited because of its HCP structure. Though the grain refined magnesium alloy exhibits superplastic deformation at elevated temperature, the strength decreases due to induced cavitation. This study focusses on developing the random texture of magnesium alloy and causes relatively high plastic deformation even at room temperature. Random texture is produced through newly proposed accumulative diffusion bonding process using commercial AZ91 magnesium alloy sheets. Tensile and V-bending tests reveal that the enhanced ductility of the produced magnesium alloy sheet.

Abstract: Superplastic Zn-22Al alloy foams were manufactured through the melt foaming process using titanium hydride powder as a foaming agent. The compressive properties of the Zn-22Al foams were investigated under quasi-static and dynamic loading conditions. Experimental results show that the flow stress and the energy absorption of the Zn-22Al foam significantly increased with increasing the strain rate. At high strain rate region, the energy absorption of the Zn-22Al foams is also larger than that of conventional aluminum foams. These behaviors are due to superplastic deformation of cell walls.

Abstract: Potential applications of superplasticity for lightweight metal foams are reviewed in this paper. Metal foams have been used for lightweight structures, biomedical implants, filters, heat exchangers, sound absorbers and mechanical damping devices. Superplasticity has advantages on metal foaming process and mechanical properties of metal foams. Four examples of metal foams combined with superplastic forming are presented; (i) Enhanced foaming under internal stress superplastic condition, (ii) Superplastic diffusion-bonding of metal foams, (iii) Superplastic forming and foaming and (iv) Superplastic Zn-22Al alloy foam for energy absorbing material.

Abstract: Lightweight aluminum foams are attractive energy absorbing material for automotive machines. Strength of aluminum foams manufactured through casting process is not so much high as dense aluminum alloys due to difficult alloying. Ductility of aluminum foams manufactured through powder metallurgical process is low due to fine oxide dispersions. In this paper, we introduce new metallic foam having excellent energy absorbing property. Closed-cell Zn-22 mass%Al eutectoid alloy foams are manufactured through powder metallurgical process. The Zn-22Al alloy is known as typical superplastic material and shows superplastic deformation below 523 K, even at room temperature. Using titanium hydride powder as a foaming agent, the porosity as high as 60% is achieved. Solution treatment followed by quenching causes ductile compressive deformation at room temperature. In addition, the absorbed energy of the Zn-22Al foams are much larger than those of conventional aluminum foams.

Abstract: Lightweight metallic foams are an attractive material having excellent energy absorption and acoustic damping. The density of magnesium is the smallest among structural metallic materials, and is about two third of the density of aluminum. It is, however, difficult to produce magnesium foams by conventional process because of their chemical activity. This paper provides a novel manufacturing process of magnesium foams. Accumulative diffusion-bonding process can produce a magnesium matrix composite (preform) containing titanium hydride (TiH2) particles as a blowing agent. Foaming tests of three magnesium alloys, AZ31, AZ91 and ZA146, revealed that low solidus temperature is effective to produce fine cell morphology. Chemical composition is significantly important to optimize the cell morphology of magnesium foams.

Abstract: A new application of superplasticity was proposed in the manufacturing process of metal foams. Preform sheets were manufactured using superplastic 5083 aluminum alloy sheets through accumulative roll-bonding (ARB) process. Microcellular aluminum foam plates with 50% porosity were produced through solid-state foaming under the superplastic condition. The cell shape was oblate spheroid, which is effective to reduce the thermal conductivity. The present aluminum foam plates have a potential as an excellent heat insulator.

Abstract: Using commercial AZ31 magnesium alloy sheets, we produced a foamable preform sheet containing titanium hydride (TiH2) powder through diffusion-bonding and hot-rolling of four cycles. Heating the preform sheets in Ar atmosphere, we obtained closed-cell magnesium alloy foams with various porosities. The foamed specimen at 883 K showed the maximum porosities of 77%.

Abstract: Aluminum foams having extremely low densities offer a large potential for lightweight structural materials. New manufacturing process without expensive aluminum alloy powder has been developed using conventional bulk aluminum alloy sheets. Preform plate containing blowing agent particles is first manufactured through accumulative roll-bonding (ARB) process. By heating the preform plate, closed-cell aluminum foams having various porosity and cell morphology are produced. It was revealed that ARB processing condition is significantly important to produce suitable aluminum foam with high porosity and uniform pore distribution. Present manufacturing process also possesses a potential to apply to many other metal and alloy foams.