To eliminate casting defects caused by sand mold, it is necessary to use molding sand with appropriate properties and produce the sand mold under the suitable molding conditions. However, in blow molding with compressed air, sand mold properties are not enough controlled and the molding conditions are not optimized. It is therefore necessary to develop and effectively utilize molding CAE for these processes.

  In this study, the interactive behaviors between green molding sand and compressed air during the blow process with green molding sand were analyzed using a laboratory type blow molding machine. Pressure transducers were installed in the molding flask to measure the compressed air and molding pressure. The blowing behaviors of the molding sand due to the air pressure were observed using a video camera. From the obtained results, the interactive behaviors between the green molding sand and compressive air were analyzed by varying the vent arrangements and blow pressures. The effects of air pressure on conveyance of mold sand particles or compaction of molding sand layers were clarified. This knowledge is useful for developing molding CAE software using green molding sand.

  In diecasting, the J factor is an index defined by the gate speed and gate shape. In this work, the J factor was increased using a diecast piston mold (high J factor method) to determine whether this method can reduce porosities in products. In the experiments, the J factor was adjusted by varying the gate shape and injection speed. Porosity was quantified as the volume fraction of porosity in a specific region measured by micro CT. In all cases, the porosity in thick parts of pistons was reduced. Next, the high J factor method was used to examine the transmission of molten metal pressure to the overflow part. At higher J factors, the surge pressure increased linearly and pressure was transmitted more efficiently. Additionally, the gas content in the product increased at high J factors obtained by increasing the gate speed. However, the gas content in each part of the product was almost constant regardless of porosity amounts. Secondary ion mass spectroscopy (SIMS) was also used to measure amounts of gas microscopically. Hydrogen and nitrogen were observed in the base material in parts where no porosity was observed. Although increasing the J factor changed the shape of porosity from a shrinkage shape to spherical, dendrites were observed for both porosity shapes. The above results suggest that the shrinkage shaped porosity and spherical porosity were formed by the same process. The experimental results were quantitatively reproduced using casting CAE software with a nucleation model for porosity formation.

  The size of defects in castings affects mechanical properties such as fatigue strength. These properties are the most important properties used for designing aluminum alloy casting components, and usually increase with decreasing size of internal defects. Large internal defects mainly form due to the volumetric shrinkage of melt at the last solidified position. In this study, we therefore examined the possibility of generating microbubbles in aluminum alloy melts for dispersing internal defects in castings.

  Ultrasonic treatment was used for generating nitrogen or argon microbubbles in the melt and was found to be suitable for forming fine gas porosities dispersed in castings. The fine gas remained in the melt for 3600 s, and the generated argon gas was detected from the porosities in the castings. The ultrasonic treatment could also remove inclusions and hydrogen in the melt. Moreover, the fine gas porosities in castings did not decrease the tensile strength of the castings.

  Al-Mg based alloy is a strong candidate material for automobile body parts because it does not require heat treatment and shows excellent ductility. In our previous studies, we found that Al-4.5Mg-1.0Mn based alloy added with 0.2% Si, 0.020±0.005% Sr, 0.008% Ti, and 0.016% B has both around 15% fracture elongation and low hot tearing susceptibility. However, the influence of hydrogen gas content in molten alloy on the susceptibility of Al-4.5Mg-1.0Mn based alloy has not been quantitatively investigated. In this study, the amount of hydrogen gas in the molten metal was varied under two conditions : a large amount (1.0cc / 100gAl) and a small amount (0.3cc / 100gAl). Through this, the influence of both hydrogen gas content and Sr, Ti, and B additions on the hot tearing susceptibility of Al-4.5Mg-1.0Mn based alloy was investigated. When there is a large amount of hydrogen gas, the addition of Sr, Ti, and B reduced hot tearing susceptibility. On the other hand, when there is a small amount of hydrogen gas, the addition of Sr, Ti, and B did not reduce the susceptibility. These results suggest that a certain amount of hydrogen gas is required to reduce hot tearing susceptibility by the addition of Sr, Ti, and B to Al-4.5Mg-1.0Mn-0.25Si alloy.

  Non-heat treated Al-Mg based alloy is expected to be applicable as automotive body parts material due to its ductility. In this study, lower link arms, an automotive rear suspension part, were produced by high pressure die casting using Al-4.5Mg-1.0Mn based alloy. The influence of both the amount of die lubricant and added amount of Ti, B, and Sr on the hot crack length of the lower link arm was investigated. It was found that, as a result of changing the amount of the die lubricant, the crack length became longer when the die lubricant coated was above a certain amount. As a result of adding variable amounts of Ti, B, and Sr under the same die lubricant coating conditions, the following two points were suggested. First, the addition of Ti, B, and Sr reduced the crack length at the side of the lower link when the mold temperature was controlled to above 190℃. On the other hand, the addition of Ti, B, and Sr did not reduce the crack length at the bottom of the lower link. This might be caused by the difference in the crack mode at these measurement points.

  Non-heat-treated Al-Mg based alloys are considered to serve as a good candidate material for automotive body parts due to their outstanding ductility. In our previous studies, we found that Al-4.5Mg-1.0Mn based alloy added with 0.2% Si, 0.020±0.005% Sr, 0.008% Ti, and 0.016% B has both around 15% of fracture elongation and low hot tearing susceptibility. In this study, a large automotive suspension part called strut housing was produced by high pressure die casting using this Al-4.5Mg-1.0Mn-Si alloy. Tensile test specimens were obtained from the gate side, center side, and overflow side of the strut housing to investigate 0.2% proof stress and fracture elongation. As a result, the fracture elongations for the gate side and center side were around 15%. On the other hands, the elongation of the overflow side was less than 5%. This is due to the occurrence of cold shut because the temperature of the molten alloy dropped below the liquidus temperature when the molten alloy passed through the overflow side of the strut housing. It should be necessary to maintain the molten alloy's temperature above the liquidus until the molten alloy fills the cavity in the use of non-heat-treated Al-Mg based alloy for large automobile parts.