Spheroidal graphite cast iron is widely used for various purposes due to its excellent mechanical properties. The majority of the destruction of machinery and structural members is due to fatigue. The starting point of destruction is parts which change their form such as notches. Fatigue tests in previous researches have suggested that spheroidal graphite cast iron with adjusted RE content does not reduce fatigue strength even if the RE content is reduced to 0.3%. However, the effect of RE content on notches is not clear. Therefore, in this study, spheroidal graphite cast iron was produced using a nodularizer with different RE contents and subjected to plain bending fatigue test, and the influence of RE content on notch sensitivity was investigated.

  In FDI and PDI, the fatigue strength differed by 19 to 20% depending on the presence/absence of RE, and this difference in the fatigue strength was small at 8% maximum in the notched specimens. As a result of observation of the fracture surface, FDI and PDI specimens not containing RE showed reduced fatigue strength due to casting defects. Since the crack propagates from the bottom of the notch, it can be inferred that there was no difference in fatigue strength. It was clarified that the notch sensitivity coefficient becomes high in the vicinity of 10⁷ times. From this, PDI shows higher notch sensitivity than FDI with or without RE.

  Demands for aluminum alloy are increasing in various fields because it is light and strength. Especially, JIS AC7A represented by Al-Mg alloy in aluminum casting has high corrosion resistance and strength. On the other hand, casting factories prepare casting materials (JIS AC7A) by mixing ingot and returned materials. In some cases, silicon is found contained when the chemical composition of aluminum alloy is checked. The increase in silicon in the Al-Mg alloy decreases mechanical properties. In this study, in order to control the quality of the molten metal, we investigated aluminum alloy material with changed silicon content by the vacuum gas test and the K-mold method, which are melt quality evaluation methods. As a result, it was difficult to distinguish the difference in silicon content in the observation results of the vacuum gas test. But as the amount of silicon increased, the breaking angle of the K-mold specimen changed. As the amount of silicon increased, the breaking angle decreased and when the amount of silicon in the alloy was 0.17% or more, the specimen broke easily. Furthermore, according to the observation of metallic microscope, we found that Mg₂Si forms at the grain boundary, and as the content of silicon in the alloy increases, Mg₂Si also tends to increase. There was a correlation between the amount of silicon and the breaking angle. The breaking angle evaluation method using the K-mold specimen can be used for screening silicon contamination in AC7A alloy.