In order to clarify the effects of Si, P and mold temperature on the reverse segregation layer thickness in Al-Si system alloy castings, investigations were carried out by microstructure observation. The results are as follows. The reverse segregation layer was observed in Al-7% Si alloy but not Al-12.6% Si alloy. The reverse segregation layer thickness of Al-7%-0.002%P alloy was thicker than that of Al-7%-0%P alloy. The solidified shell thickness was thin for high mold temperatures. The reverse segregation layer thickness was determined from the solidified shell forming time. The eutectic silicon in the second layer (solidified shell) of Al-7%Si-0%P alloy had a round shape similar to that seen when solution treatment is carried out during the formation of air gaps. The formation mechanism of four layers on the surface in Al-7%Si-0%P alloy was also reviewed.

  Three-dimensional element concentration mapping of Al-Cu alloy was carried out using the K-edge subtraction imaging technique. Spatial inhomogeneity of copper concentration was evaluated using a solution heat-treated sample. The average value of copper concentration was 1.57% for the whole sample. From the observation of three-dimensional images, the copper concentration seems to be homogenized by the solution treatment. By evaluating several unit cubes of 20μm in one side, the variation of the copper concentration which varies between 1-2% was obtained. The three-dimensional concentration mapping revealed in more detail than before that homogenization by solution treatment at high temperatures for a long time appears to be insufficient. Furthermore, the influence of sample size was also evaluated by applying the K-edge subtraction imaging technique to materials with the same composition but different sample sizes.