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For making sound aluminum
castings, it is an important problem to clarify
the shrinkage morphology of various raw ingots.
The aim of this study is to clarify the main factors
affecting the shrinkage morphology of Al-Si system
casting alloys by examining their shrinkage behavior.
Eamination of the shrinkage cavities in the cylindrical
castings for secondary diecasting alloy ingots showed
that the soluble gas in the melt as well as the
alloying elements remarkably affected the change
in shrinkage morphology. By using the method newly
developed for evaluating the shrinkage morphology
of hypoeutictic alloys quantitatively, the effects
of silicon content and gas amount were investigated.
It was clarified that the total amount of three
kinds of shrinkages, that is, porosity, interior
and exterior shrinkages, was constant in the alloys
with the same composition although each kind of
shrinkage was affected by the gas in the melt. It
was also confirmed that the relations among the
three kinds of shrinkages were varied with the silicon
content. Furthermore, the change in the ratio of
the shrinkages with the amount of gas was found
to be dependent on the pore formation.
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