High hopes are placed on the semi-solid process as a near net shape forming method for producing high performance products. However, the semi-solid process has such disadvantages as poor formability in low fluidity, and difficulties in making the semi-solid slurry. In the previous work, we tried to make the semi-solid slurry by applying mechanical vibrations, and successfully obtained slurry with small and spherical solid particles. In this study, we evaluated the fluidity of JIS AC4CH aluminum alloy slurry made by applying mechanical vibrations. We also improved fluidity by applying shear stress to slurry at the gate of the mold, and investigated the effects of shear rate on the fluidity of the slurry. The slurry was prepared by applying mechanical vibrations in the frequency of 50Hz and acceleration amplitude 166.6m/s² (17G). The fluidity was evaluated by injecting slurry into a metallic mold with spiral cavity through a gate, as flow length into the cavity. The shear rate at the gate was controlled by changing the thickness of the gate from 1.0mm, 2.2mm, and 4.0mm. The fluidity of the slurry made by applying mechanical vibrations had about 25 to 40% of the fluidity of liquid aluminum. On the other hand, by applying shear stress at the gate, the fluidity was increased by approximately 30%. The α-phase particles in the specimen became fine and spherical with increasing shear rate. As just described, semi-solid slurry with high fluidity can be obtained by the addition of mechanical vibration and applying shear rate. Moreover, the mechanical vibration slurry indicated approximately the same fluidity as electromagnetic stirring slurry by applying high shear rate and high casting pressure. This method is expected to enable the production of the semi-solid forming products with complex configurations.

  Minute amounts of phosphorus impurities in hypo-eutectic Al-Si alloys have adverse effects on mechanical properties, shrinkage characteristics, and reverse segregation. The authors showed that dephosphorylation is possible by adding sodium improvement flux to the molten metal and removing the dross after vigorous stirring. In this experiment, attempts were made to put the dephosphorylation process into practical application by melting 500kg of commercial alloy ingot (JIS-AC4CH) in an industrial electric furnace. Use of a rotary degassing apparatus was tested as a stirring method, after addition of sodium improvement flux. Industrial problems were reviewed using this method, and the following results were obtained.

  1) The process can decrease phosphorus content from 12ppm to 2ppm in molten metal. 2) For the amount of flux to be added for the treatment, 5% and 1% were found to be too much, and 0.2% and 0.5% too little. Moreover, treatment time of 10 minutes was too long. 3) The process can decrease phosphorus content, gas content, and inclusions at the same time. 4) The phosphorus content increased from 2ppm to 8ppm with long molten metal holding time, which may be due to contamination from graphite crucible. 5) These findings confirm that dephosphorylation using the rotary degassing apparatus is useful for industrial purposes.

  Most aluminum scraps are disposed or exported overseas because they are difficult to recycle due to oil adhesion and their coating. Conventionally, these scraps are pretreated to eliminate water and oil by centrifuge and drying in a rotary kiln furnace. However, we have developed a recycling system which can remelt aluminum scraps without pretreatment, produces no smoke, uses less energy, provides high aluminum yield. This system also enables recycling of scraps such as chips and foil with high efficiency. During the recycling process, the oil and water contents affect energy consumption to a great extent. Although oil contamination helps saves energy by combustion, energy consumed by water evaporation has a negative effect. The smoke generated during the melting process transforms the melting atmosphere into a less oxidizing atmosphere. Consequently, these contaminations contribute to improving the melting conditions favorably. The recycled ingots include small nonmetallic inclusions and their composition is within the range of JIS standards.