Low-pressure casting has been simulated by engaging pressure from 0 to 1 kg/cm~2 on the feeder of the A356 castings in a simply-made permanent mold. Thermal variables were obtained by thermal measurements and used to analyze the feeding behavior during solidification. The parameter of G~(0.38)/Vs~(1.62) for A356 alloy (G is the thermal gradient and V_s is the solidus velocity) is employed to estimate the value of local pressure drop during solidification and to explain the porosity distribution of the castings with gauge pressure. The result indicates that engaging pressure on the solidifying alloy lowers the solidification time and directional solidification as well as increases the local pressure drop. As the gauge pressure is not greater than the local pressure drop of the casting, the porosity forms and the quality of the casting with gauge pressure may be worse than that without gauge pressure. Contrarily, the porosity content decreases with the increase of the gauge pressure when the local pressure drop is overcome by the gauge pressure.
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