The development of a software was carried out for the solidification phenomenon of rapid cooling. The computer simulation by the software can estimate the effect of the solidification by rapid cooling and the solidified structure for Al-2 to 8 mass%Pb alloys. An outline of the simulation is as follows: The cooling process by successive temperature steps was applied to the continuous cooling process in the solidification. The solidification and reaction process were analyzed by four proposed models. In the phase separation reaction, L
1→L
2s+(L
1), spherical liquid phases L
2s of
CH%Pb are randomly distributed throughout the liquid phase L
1 of
CL%Pb, and the liquid L
1 around the L
1/L
2s interface can be supercooled by
1ΔT1. A total amount of the liquid L
2s increases as the coarsening and sifting-out growth proceed. In the monotectic solidification, L
1→Al+L
2m+(L
1), the solid phase aluminum is nucleated in the liquid L
1 supercooled by
ΔTm due to rapid cooling. Then, by the diffusion event between an Al-rich diffusion layer around the liquid L
2m and a Pb-rich diffusion layer ahead of the solid aluminum, the solid aluminum is grown in a shape such as an ellipsoid, and dropletes of liquid L
2m of
CH′%Pb form locally around its solid aluminum. At the completion of the monotectic solidification, the retained liquid phases L
2m and L
2s are entrapped or isolated by the growing solid phase. Their liquid pools L
2 solidify individually, L
2→Al+(L
2), or grow by sifting-out growth with decreasing temperature. Then, at the supercooling by
ΔTd below the eutectic temperature, the solid phase lead form from the retained liquid pools of 100%Pb as divorced eutectics, L
2→Pb. In that case, the phase transformation and concentration change in phases were considered to follow the equilibrium phase diagram. For cooling rates of 10
2 K/s to 10
3 K/s, the calculated structure was in good agreement with the experimental one.
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