A classical rigorous solution of solidification of pure metals as modified for alloys with a finite solidification temperature range was used to examine the behavior of temperature gradient G (K·m-1) at the solidus in the mushy zone and solidification velocity V (m·s-1), assuming an infinitely thick mold and casting. The ratio G/V, which controls porosity formation, constitutional supercooling or columnar crystal growth, is constant independent of time. The ratio increases by slow cooling through the use of a poor conducting mold material or at a high mold temperature. The relation among G, V and other major thermal variables was presented in dimensionless forms. Since the discussion is based on the assumption of infinite thickness, the results are applicable to real castings only in the early stage of solidification.
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