The change of the eutectic silicon inter lamellar spacing in Al-Si alloy is one of the factors changing the alloy's mechanical properties. This paper aimed to clarify the effects of the relationship between the eutectic solidification time (t) and eutectic cell number (n) on this eutectic silicon inter lamellar spacing (λ) on the surface of a permanent mold casting made of Al-7%Si alloy. The results are as follows.
  1) The eutectic cell number (n) is affected by the quantity of nuclear matter in the molten metal and super cooling caused by the mold.
  2) The eutectic silicon inter lamellar spacing (λ) increases with the increase in the eutectic cell number (n) and eutectic solidification time (t).
  3) The parameters in the above 2) were found to have the following relationship. λ ＝ k・n^1/4・t^1/2.

  Due to transcription of the die heat check and exposure of interior defects by machining, etc., there exist defects on the surface of die casting parts, which often act as the origin of fatigue failure. Fine particle bombardment (FPB) highly improved the 10⁷ cycles fatigue strength of ADC12 die-cast. In the FPB treated die-cast, a thin modified layer of about 5μm in depth was formed on the surface and filled the surface defects. Both the application of compressive residual stress in the surface regime and these surface modifications resulted in the higher fatigue strength.

  In order to determine the influence of matrix structure on the corrosion rate of spheroidal graphite cast iron, a corrosion test was performed in sulfuric acid solution of pH 2. The pearlite matrix area was changed by heat treatment. The corrosivity of spheroidal graphite cast iron was evaluated by corrosion potential, corrosion rate and observation of the surface of the specimens by SEM. Ferrite in the lamellar structure of pearlite dissolved preferentially. The corrosion rate of the pearlite matrix was higher than that of ferrite. The corrosion potential became less noble with the increase of the prarlite area. These results indicate that the increase of pearlite promotes both cathodic and anodic reactions.