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Permanent mold (PM) and semi-solid (rheo) casting in ductile iron castings (DIC) were studied, and the microstructure was aimed to be chill free in as-cast condition. Denitrification was conducted understanding solubility properties of nitrogen in base molten iron, and re-nitrification was strictly avoided during molten treatment by Mg alloy. As the results, chill-free knuckle castings were possible with both casting methods in as-cast condition. The knuckle castings had no shrinkage cavity also. The solidification time by rheocasting was shorter than that of PM casting. It was approximately one in two and a half. The castings had ultrafine spheroidal graphite which were mostly under 10 µm. The graphite structure by rheocasing method was finer and more uniform than those of PM casting. The tensile strength in castings with both casting methods was approximately 1.3 times keeping elongation over 10% comparing with conventional sand knuckle castings. It was concluded that free nitrogen (NF) promoted chill formation, and chill could be avoided by promoting denitrification and minimum re-nitrification.

Despite the lightweight demands, precision die casting products with high dimensional/ die-transcriptional accuracy is still made by zinc die-casting, because the conventional aluminum die-casting cannot satisfy the requirement. While light weight precision die casting demand for electric devices /automobile parts has been encouraging the material replacement from zinc to aluminum, it cannot be realized yet. We applied the Semi-Solid die casting technique to the precision casting, and verified possibility of replacement of the material from zinc to aluminum

For the semi-solid casting process it is very important to make high quality slurry with high speed and low cost. Recently the double-axis-electromagnetic stirrer is developed as the slurry-making tool. This stirrer has rotating magnetic field (RMF) and linear traveling magnetic field (TMF). This new technology shows several advantages in the quality of slurry. The cup design is also important to make uniform quality slurry. In this paper the new stirrer and its advantages from test report and technology of cup design is introduced.

Recently, semi-solid slurry making method using metallic vessels, called "Cup-method", have been studied by the authors. In this method, semi-solid slurry with globular and fine structure is obtained only by pouring molten metal at certain temperature into a metallic vessel which is designed for desired slurry volume and solid fraction of the slurry. The method provides us shorter slurry making time and finer microstructure of α grain with around 50 μm in its size. However, the cup-method requires precise control in the slurry making condition; therefore it is difficult to obtain the homogeneous microstructure in the slurry, especially for the larger slurry. In this study, mechanical vibration was introduced to enhance homogeneity and fine microstructure generation. As a result, mechanical vibration provides the fine and homogeneous distribution of microstructure for wider slurry making conditions. Fine and non-dendrite structure of the slurry could be obtained even by using higher superheated melt, while the conventional method without vibration showed coarse and dendritic microstructure in the similar conditions.