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Abstract Cast aluminum alloys are widely applied in aero and
auto industries because of their good mechanical properties,
light weight and high strength to mass ratio. The castability
and mechanical property of aluminum alloy degrade due to the
porosity defect. In order to decrease the porosity of cast
aluminum and improve casting quality, researchers engage in
knowing the mechanism of porosity formation by experiments and
physical modeling.The main purpose of this study is to introduce
kinetic effect of hydrogen diffusion to the previous model of
interdendritic fluid flow based on the Darcy''s law as well as
surface tension in porosity formation. The volume percent of
porosity (Vp%) is formulated in this study. Previous data
from Chieu''s plate sand castings and Jain''s cylindrical metal
mold were used to verify this theory. It is found that local
pressure drop, thermal gradient and pressure of surface tension
effect are important factors in porosity formation. In this
study the hydrogen content exerts the influence on the porosity
formation, and it is assumed that the diffusion coefficient of
hydrogen is a function of the solidus velocity. Since hydrogen
solubility in the solid is much less than it is in the liquid
phase, it is proposed that hydrogen concentration increases in
the remaining liquid because of the rejection of hydrogen in the
liquid. When the dissolved hydrogen overcomes the atmospheric
and hydrostatic pressures, and the pressure of surface tension
effect, porosity will form.
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