The strength properties of spheroidal graphite cast irons are generally explained by the area percentage of ferrite and pearlite. However, it was found that the strength properties of pearlitic spheroidal cast iron with heavy section cannot be explained only by the area percentage of pearlite. Therefore, we clarified the relation between strength properties and the pearlite layer spacing and diameter of pearlite blocks as factors that affect the strength properties. As a result, it was found that the strength properties of spheroidal graphite cast iron with heavy section are strongly affected by the perlite layer spacing and have a linear relation with the inverse of perlite layer spacing. The perlite block diameter depended on the cooling rate and increased with decreasing cooling rate, which contributed to the brittle fracture tendency. The relation between perlite block diameter and strength properties showed that the Hall-Petch relation holds and can be used to evaluate strength properties.

  A technique for measuring the thermal conductivity of molten metals using the hot disk method with minimal influence of thermal convection was developed. First, the thermal conductivity of molten Bi, Sn, and Al was measured by employing a measurement time of less than 0.8 s for molten Sn and Bi, 0.5 s for molten Al. The measured results were in good agreement with the recommended values by Assael et al. and Touloukian et al., and those measured in microgravity. Next, the thermal conductivity of molten Al-Si alloys was measured. The thermal conductivity of molten Al-Si alloys was significantly lower than that of solid Al-Si alloys, and increased with increasing temperature. This tendency can be explained by the Wiedemann-Franz law. Moreover, the thermal conductivity of molten Al-Si alloys was found to decrease with increasing Si content.

  The objective of this study was to optimize the cooling conditions after solution treatment of the JIS AC4CH aluminum casting alloy, and the effects of the temperature range cooled at 0.5℃/s on the microstructure and mechanical properties were investigated. The temperature range of the cooling and cooling rate were simultaneously adjusted by heating using a high-frequency induction heating apparatus and cooling by blowing air. In particular, cooling at 10℃/s (CR10) was used as the basic cooling rate, with a rate of 0.5℃/s (CR0.5) used for a portion of the temperature range. The scanning electron microscopy (SEM) observations of the specimens after cooling revealed that rod-like precipitates formed in the specimens that were cooled at CR0.5 in the range of 400-250℃. In the specimen that was cooled at CR0.5 from 500 to 450℃, granular or rod-shaped precipitates with a small aspect ratio were observed. From the results of a scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) investigation, the former were identified as the Mg₂Si intermediate phase, and the latter were composed mainly of Si. An electron probe micro analyzer (EPMA) was used to measure the Mg and Si concentrations in the primary α-Al phase. In the case of the temperature range for CR0.5 cooling above 350℃, the Si concentration decreased significantly as the temperature range of CR0.5 cooling increased. Considering the Si concentration distribution and diffusion distance in the primary α-Al phase, this decrease in the Si concentration could have been caused by the diffusion of Si atoms to the eutectic region. The 0.2% proof stress and tensile strength values after the artificial aging of a specimen that was cooled at CR0.5 from 400 to 350℃, where a coarse Mg₂Si intermediate phase precipitated during cooling, were approximately 10% lower than those of a specimen that was cooled at CR10 over the whole temperature range.

  To make sound cast iron castings, it is necessary to use the green sand mold with good mold properties. The green sand mold requires comfortable green sand properties, which are compactability (CB) index, moisture content, permeability, bulk density, and so on. The green sand test piece of ø50 × 50mm is used to measure these properties. Therefore, it is important how the green sand test piece is made. In this study, three types of test piece equipment were used to make green sand test pieces by changing the making method, squeeze speed, squeeze pressure, and sand type. The static and dynamic properties of the test piece are measured. The dynamic properties are analyzed using Cooper-Eaton’s equation. It was clarified that the static properties were affected by the making method, squeeze speed, squeeze pressure, and sand type. From the experimental analysis, it was clear that the dynamic properties of the green sand were divided into two types the rearrangement mechanism and the deformation mechanism. The squeeze speed, squeeze pressure, and sand type affected these two mechanisms. This dynamic analysis result showed that the green sand mold with high compacting density can be obtained under the conditions of relatively slow squeeze speed and high squeeze pressure.

  There are casting defects caused by insufficient behaviors of heat transfer and solidification, such as a shrinkage cavity and porosity. To obtain a sound casting, the prediction of the location and size of defects using the casting CAE simulation is a useful and effective method. As the current defect prediction in casting CAE is limited to qualitative evaluation, it is necessary to predict defects quantitatively. Conical mold castings are suited for predictive verification of simulations because they are prone to shrinkage cavity defects. This study performed shrinkage evaluation experiments on aluminum alloys using a conical mold. The pipe-like internal shrinkage that occurred in the center of the casting originates from the reinstallation of the stopper, and it clarified that breaking the oxide film affects the internal shrinkage. Further, the shrinkage cavities were estimated using Eulerian and Lagrangian casting CAE software. Comparison with experimental results showed that it is difficult to match the boundary conditions in the simulations to the actual phenomena.