Unidirectional solidification experiments have been carried out in Al/Al₂O₃ composites by using the zone-melting process. The experimental results show as follows. When the volume fraction of Al₂O₃ particles is 5∼20vol %, particles can be distributed uniformly in the solidified samples. But particle settling still occurs in the liquid, and becomes severer as the particle volume fraction decreases. However, when the volume fraction of the particles is more than 20∼22 vol %, no further settling occurs under a solidification velocity of 8∼16 mm/h. The solidification rate has a very small effect on the settling height with the same particle contents. In order to investegate the interaction of solid/liquid interface and particles, a main solidification experiment was carried out using the samples made in the above mentioned experiment. The Al₂O₃ particles are pushed by the growing solid phase under a solidification velocity of 2mm/h. The particles are mechanically entrapped between cells, and distributed along the crystal grain boundaries.

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  The notched tensile properties of AC4CH alloy, which was often used for structual parts were investigated. The following results were obtained. The notch coefficient was less than 1 and notch-sensitivity was negative. The notch coefficient increased slightly as defects increased. The notched yield ratio, which corresponded to fracture toughness, decreased with increasing 0.2% proof stress, while the notched yield ratio increased with decreasing Fe content.

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  The temperature dependence of thermit type reaction of molten aluminum and silica was investigated. Reacted depth was measured for amorphous silica rods immersed in pure molten Al or Al-5 mass%Mg alloy at various temperatures up to 1273K for a certain period. It is clarified that the reaction rate peaks around 1173K, and the rate at 1273K is 10 times lower than that at the peak temperature. Reacted substrates formed above the peak temperature has coarser microstructure than those formed below the peak temperature. Furthermore, intermediate layers are observed between the reacted substrates and unreacted silica. This indicates that the diffusion of aluminum into silica beyond the thermit reaction may have caused the decrease in the rate above the peak temperature.

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  Inmold process is a graphite spheroidization treatment carried out a reaction chamber in a mold set with special spheroidizers beforehand. A new melt combination process, which can produce new functional iron materials, was developed by the authors’ further studies. In this new process, both the spheroidized and inoculated melts are collided with each other in the mold cavity to form a characteristic transition graphite structure. One side of the material has the specific properties of spheroidal graphite cast iron and the opposite side has that of the flake graphite cast iron. In this study, the effects of gate type and size, amounts of treatment alloy, and cross section of reaction chamber on the control of the graphite morphology from the spheroidal via the compacted vermicular to the flake in the iron structure were investigated. Besides thermal analysis of the melts, ultrasonic velocity measurement and micro-graphite structure observation were also carried out.

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  Inmold process is one of the most excellent graphite spheroidization methods in the field of ductile iron foundry today. Y block castings with functional graphite transitional structures varying from spheroidal to compacted-vermicular, flake, were produced by a modified Inmold process developed by one of the authors. The mechanism of this transitional structure was simulated by water model experiment. The gating system of hybrid cylindrical castings suitable for practical use was also investigated. The use of filter, dam and chill plate other than the ingate arrangement in the cavity, proved very effective for the control of such graphite transitional structures.

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  In the insertion of pipes in casting, internal air or gas flow cooling is effective to prevent thermal damage and structural deterioration of the inserted pipe. In this report, internal air cooling was carried out for a mild steel pipe inserted in ductile cast iron. To achieve good metallurgical bonding at the interface and protection of the inserts, delayed cooling was proposed. Solidification analysis was also performed to discuss the experimental results. In the experiments with melt/insert volume ratios, VR, of 10, 30 and 100, air cooling was effective. Grain growth of the pipe structure was suppressed and the carburized zone was reduced to half in the VR 30 and VR 100 specimens. Cooling with a 100s delay had almost the same effect, with improved bonding at the interface. The calculated solidification progress and concept of liquid phase contact time, LCT, gave a good explanation of the experimental results. The internal cooling method is also effective for improving the microstructure of castings, decreasing graphite nodule size, and increasing the nodule counts markedly.

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  The effects of chemical composition, microstructure and testing conditions on the so-called 673K embrittlement in spheroidal graphite cast irons were examined in detail. The observation of fracture process shows that the embrittlement is not due to dynamic strain aging (blue embrittlement) but intergranular fracture. It is found that the embrittlement can be suppressed by reducing the Mg/P ratio to less than 1.5.

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  Casting experiments of single crystals are carried out by the mold withdrawal unidirectional solidification. Commercial stainless steels SUS316 and SUS347 single crystals are grown successfully, but not SUS304 and SUS321. Single crystal growth is closely connected with alloy elements, and it is clarified that the single crystal castings can be obtained at an equivalent value ratio (Cr eq/Ni eq) of below 1.85. Modified stainless steels SUS304 and SUS321 in the compositional range of JIS standards with Cr eq/Ni eq at about 1.5 can grow single crystals. Furthermore, by using modified stainless steel SUS316 with Cr eq/Ni eq of 1.47, single crystal round bar of 20mm dia. and single crystal pipe of 28mm outerdia. , 20mm innerdia. are sucessfully manufactured.

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  A new technique of two dimensional mold filling simulation based on the Direct Finite Difference Method has been developed. Non-orthogonal elements can be employed in this technique so that the original complicated and thin shape of a casting, including the gating system, can be retained in its simulation model. Pressure points are located at each centroid of the rectangular element while fluid velocity vectors are at vertexes which are the representative points of nodal regions formed around the vertexes. The momentum equation is discretized in each nodal region while the mass conservation equation is discretized in element. Two dimensionless parameters β_ν, β_s are defined to predict the free surface movement more accurately and mass conservation in the free surface regions is solved explicitly by using these parameters. Some numerical mold filling examples, namely die casting of a disk-like cavity and gravity casting of a curved gating system, showed promising results of the proposed technique.

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  The use of filters offers foundries a means of cost-effective casting production. Namely this yields reduction in inclusions entrapment in castings which results in defective castings that must be scrapped. Filter setting in the runner also helps control runner flow pattern and prevent formation of dead space for flow. To find a clue to reasonable inclusions removal by filter, the relation between inclusions removal and flow behavior has been studied with two setting patterns of filter. The inclusions removal capacity of ceramic foam filter and the distribution of captured particles in the filter are estimated by making use of water model experiment and the simulation using the SOLA-MAC method. The simulation results are seen to be reasonable comparing with ductile iron casting experiments.

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