A detailed study of magnesium distribution in the microstructure of spheroidal graphite iron was conducted using a Computer-aided Micro Analyzer (CMA). The results showed that magnesium segregated in a halo-like form at the site between the eutectic graphite core and secondary graphite ring in graphite nodules. The graphite ring was in the form of a three-dimensional graphite shell. The halo-like distribution was concluded to be the trace of a magnesium gas bubble. In this study, the Site Theory has been used as one means of interpreting data. According to the Site Theory, a magnesium gas bubble in liquid iron functions as the site for the nucleation and growth of spheroidal graphite.

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  Spheroidal graphite cast iron composites with SiC particles dispersed in the surface region were made by vacuum assist casting. Although melt infiltration could not be carried out when the melt was poured without vacuum assist, it was successfully carried out by vacuum assist casting when the SiC particle volume fraction in the preform and preform thickness were optimized. The matrix of the composite was spheroidal graphite cast iron consisting of fine graphite particles, ferrite, and pearite. When the C content was 3.5mass% and the Si content was 2.5mass% in the spheroidal graphite cast iron, a product consisting mainly of Fe₃Si was clearly observed at the interface between the matrix and SiC particles. This was formed by the reaction between the cast iron melt and SiC particles during the infiltration. The increase in Si content in the cast iron tends to inhibit reaction.

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  Gravity die castings of AC4C aluminum alloy with mechanical vibration (0-120Hz) were conducted. Columnar rod specimens (25mmΦ × 210mmL) were cast to investigate the effects of vibration and mold temperature on macrostructure, casting defects, and mechanical properties of gravity die castings. The grain size of the columnar rod casts at the mold temperature of 663K decreased from 1500μm (0Hz) to 800μm (100Hz) with the imposition of mechanical vibration. But at the mold temperature of 633K, the grain size was independent of the vibration frequency, and was about 200-300μm. The casting defects at the middle area of the specimen decreased with mechanical vibration below 70Hz in frequency. But vibrations above 80Hz led to increase in casting defects. As a result, the mechanical properties of specimens cast with vibration of frequency 70Hz showed higher UTS (ultimate tensile strength) and elongation (150MPa and 5-6%) compared with the specimens cast at other vibration conditions. The specimens cast without vibration showed a relatively large change in UTS, covering about 40MPa, when the mold temperature varied from 633K to 663K. However, no difference in UTS could be found in specimens vibrated at 70Hz even when the mold temperature dropped extensively by about 60K.

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