The solid-liquid coexisting zone was classified into two regions,
q and
p according as the fluidity of interdendritic liquid. In the
q zone in which the fraction of solid is in the range from 0 to 0.67, the interdendritic liquid can easily flow through the solids, whereas in the
p zone with solid fraction ranging from 0.67 to 1.0, the interdendritic liquid can not flow because the liquid is entrapped by the solids. The morphology of microporosities in unidirectionally solidified Al-Si alloy ingots was related to the width of the
q and
p zones and the mechanical properties of the alloy were evaluated by bending test. The width of the
p zone was comparatively large in the solidification of an Al-1%Si alloy and plate-like porosities were observed in a fracture surface even though the total volume of porosities was small. On the other hand,
p zone the width became narrower in the solidification of an Al-3%Si alloy and globular porosities were observed in a fracture surface. The bending strength and absorbed energy of specimens with plate-like porosities are related to the ratio of observed area of interdendritic separation to that of the fracture surface.
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