The effects of plate-fins added to plate-shaped aluminum casting on the directional solidification characteristics were numerically examined by heat transfer and solidification simulation, and concepts for the casting designs of aluminum heat sink were also investigated. In the end effects E/T (E : end-effective range, T : baseplate thickness) of plate-casting with added fins, there were differences depending on casting and mold materials or fin-adding conditions. Meanwhile there were cases where solidification of the baseplate finished before that of the fins under the fin-adding conditions with greater end effects. Here it is considered that the conditions with the sequence of these solidification processes may be unsuitable for manufacture by casting. These differences in both the end effects and solidification process, depending on fin-adding conditions, could be explained by considering equivalent thickness including fins. In addition, it was suggested that the fin-adding conditions with smaller equivalent thickness than the baseplate thickness especially have the potential to provide greater end effects by increasing the initial mold temperature. Furthermore, it was suggested that the plot of heat-exchanging performance versus the end effects in aluminum heat sink may be useful for the casting design.

  High purity (more than 4N) nitrogen gas can be used as a substitute gas for argon gas (5N) in molten aluminum treatment. The effects of nitrogen gas purity on molten aluminum treatment were clarified in this study.

  AC8A (modified) alloy, four kinds of nitrogen gases (2N, 3N, 4N and 5N), and argon gas (5N) were prepared.

  Equivalent removal of inclusion and fluidity were seen after molten aluminum treatment by each gas.

  In comparison to 5N argon gas, the 5N and 4N nitrogen gases had equivalent degassing ability. In applying the nitrogen gas to molten aluminum treatment, above 4N purity is required to obtain the clean molten aluminum obtained by treating with argon gas (5N).

  Solidification of hypereutectic cast iron (CE4.8) with 0.04mass%Mg was observed in-situ by using time-resolved X-ray imaging. Since holding melt reduces Mg concentration due to vaporization, the observations were performed three times for each specimen to verify the influence of Mg content on microstructure evolution. At the first run, graphite particles with spherical shape grew in the melt and were surrounded by γ-dendrite or γ-graphite eutectic. The typical diameter of graphite particles was 30μm. At the second and third runs, graphite particles with spherical shape grew in the initial stage and then transformed from spherical to flake shape before they were surrounded by γ-dendrites and γ-graphite eutectic. The reduction of Mg in the melt due to melting led to decrease in graphite nucleation. In addition, the temperature range in which the graphite particles grew as the primary phase increased with decreasing Mg concentration. The observation also suggested that Mg content in the melt influenced graphite nucleation frequency (kinetic effect), phase equilibrium of graphite-austenite-liquid phases (thermodynamic effect) and morphology of graphite. The graphite growth was followed by growth of the austenite phase which tended to nucleate in the vicinity of the graphite particles and to grow along the graphite particles. The eutectic solidification of the austenite and graphite finished behind the austenite dendrite tips.

  Since a cooling rate becomes large when the thickness of spheroidal graphite cast iron becomes thin, it becomes easy to form chill and brittlness. Increasing graphite nodule count and adding rare earth element (RE) are effective for reducing chins.

  However, ever since the permitted export amount of RE was reduced sharply in the latter half of 2010, the price of RE has continued to rise, making it difficult to acquire RE in Japan. Although exports of RE are normalizing now, the problem of stable supply of RE has fundamentally not been resolved. Therefore, in this study, the influences of trace amounts of RE element and the addition of alkaline-earth metals calcium and barium on the graphite nodule count of thin spheroidal graphite cast iron were investigated as a means of substituting or reducing RE used for manufacturing spheroidal graphite cast iron.

  When small amounts of RE were added, the graphite nodule count increased considerably. However, when it exceeded 0.02%, the upward tendency of the graphite nodule count became moderate. For the thickness of 3mm, when 0.02% RE and 0.05% Ca were added, the graphite nodule count became 800 number/mm2 and approached the graphite nodule count of 836 number/mm2 of samples (0.0432% RE, 0.032% Ca) produced using general spheroidizing agents.

  Tensile test and V-notch Charpy impact test were performed on a series of ferritized spheroidal graphite cast irons containing 1.9～3.6%C-1.6%Si, 1.9%C-1.5～4.2%Si, 3.6%C-2.1%Si and 3.3%C-3.7%Si. The ferritization treatment was made on as cast specimens with 0 to 100% pearlite by heating them at 900℃ (1173K) for 2h, cooling to 600℃ (873K) in a furnace at (900℃ (1173K)-600℃ (873K)) /24h and air cooling. The 0.2% proof stress and tensile strength of ferritized iron increase linearly with decreasing C content. The elongation becomes higher at lower C content. Charpy absorbed energy in the upper shelf also increases with decreasing C content. These effects of decreasing carbon are thought to be mainly caused by the increase in the fraction of matrix. However, the transition temperature of absorbed energy becomes higher with the decrease in C content. Graphite nodules remarkably reduce the upper shelf energy, while they significantly lower the transition temperature. Higher Si content effectively increases both 0.2% proof stress and tensile strength due to strong solution hardening ability of Si. Although the elongation decreases linearly with the increase in Si content, it shows still 20% at 4.18%Si. On the other hand, both the upper shelf energy decreases and the transition temperature becomes higher with the increase in Si content. A proper combination of C and Si content is key to the higher performance of ferrite matrix spheroidal graphite cast iron.

  Two or more RE elements are contained in commercial spheroidizers used for manufacturing spheroidal graphite cast iron.

  One of the author has reported that the graphite nodule count in 3mm thick specimens treated with a spheroidizer containing a single RE element is greater than that of the sample treated with a spheroidizer containing Ce and La.

  In this research, the microstructure and mechanical properties of cast iron treated with the spheroidizer containing La were investigated to reduce the contents of RE. In the sample treated with a spheroidizer containing 0.01% La and 0.025% Ca, the graphite nodule count became 916 number/mm², which is much higher than the graphite nodule count, 836 number/mm², of the sample treated with the commercial spheroidizer (RE0.045%). Good mechanical properties, tensile strength of 460MPa and elongation of 25%, were obtained in the Φ30mm specimen because of the increasein the effective number of sulfides acting as a substrate of graphite crystallization.

  The amount of RE could be reduced to about 1/4 compared with the RE content of commercial spheroidizers using the spheroidizer containing La and Ca.