It is known the application of ultrasonic vibration to molten metals during solidification results in the formation of fine-grained structures. We have previously reported that the fine-grained structure formed by applying ultrasonic vibration was caused not by mechanical destruction of dendrite but by promotion of nucleation. It is particularly important to apply ultrasonic vibration to the alloy crystal when it starts to solidify and cross over the liquidus. In this study, we controlled the solidified structure of Al-Si alloy in the supercooled state by applying ultrasonic vibration for a short time. After the Al-Si alloy was completely melted at 1123K, a ceramic horn was immersed and the ultrasonic vibration applied. The application of ultrasonic vibration for a short time provided fine-grained structures. Specifically, when ultrasonic vibration was applied to Al-6%Si alloy supercooled to 1K for 10 seconds, fine-grained structures were formed under the horn. It was concluded that the application of ultrasonic vibration to the molten metal in the supercooled state under the liquidus for a very short time enables control of the fine-grained structure of alloy due to promotion of instantaneous nucleation.

  Phosphorus impurity in hypo-eutectic Al-Si alloys has adverse effects on their mechanical properties, especially toughness. Moreover, it causes the shrinkage characteristics to become worse and the inverse segregation layer to become thicker. Modification treatment has been used in the past to avoid these effects. However, there are problems of over-modification of the duration of effectiveness and of the rapid increase of hydrogen. Hence, a de-phosphorization treatment using flux was tested on Al-7%Si alloy and AC4CH alloy. In addition, studies were conducted on the de-phosphorization mechanism and modification of the eutectic structure. The results were as follows. 1) It was found that the phosphorus content in the molten metal decreases with the addition of large amounts of flux and removal of the generated slag after vigorous stirring. 2) In this process, the eutectic structure is changed from un-modificated to modificated. 3) The dephosphorization mechanism is considered to be the oxidation of sodium phosphide, and its attachment and removal by the molten chloride.

  The influence of mold tilt on aluminum alloy melt flow was studied using sand molds for aluminum thin-wall plate castings. The mold tilt was changed from ＋15.5° to －15.5° at six grades. Using a heat-resistant glass plate for the upper sand mold, we observed the flow patterns through the glass plate with a high speed video recorder at 200 flames per second.

  If the tilt was negative, the melt went straight up to the end, then flowed backward. When the tilt was positive, the melt flowed while keeping the horizontal line. Nevertheless, if the mold was horizontally held, the flow pattern was unstable as expected. This result completely agreed with those of the sand mold experiments. These results can be explained by and agree with the Weber number, namely, the ratio of the surface tension and inertia.

  High strength brass pipes for bearing cage were developed by a centrifugal casting method adding machining chips. Molten high strength brass was poured into rotating mold with or without machining chips, and pipe shaped casts were obtained. It was found that high strength brass pipe can successfully be developed by centrifugal casting using machining chips. It was also revealed that the grain size of casts was refined by the addition of machining chips, and hardness of casts was improved. Since some pores were found on the outer region of pipes fabricated with the machining chips, wear volume at the region was increased. The proposed casting method has some advantages, i.e., saves energy, refines grain size, and enhances hardness.