The effect of magnesium loss on the kinetics of infiltration of cylindrical SiC_p porous preforms by an Al–Si–Mg alloy was investigated. Infiltration of SiC_p preforms is preceded by an incubation period, which is significantly dependent on temperature, with incubation time decreasing as temperature increases. The activation energy required to initiate infiltration is 637.2 kJ/mol. The cross-sectional area of the cylindrical preform infiltrated can be predicted by a linear regression equation. Results also show that temperature is the process parameter that most significantly affects the degree of infiltration and that the combined effect of the parameters, time and temperature, is negligible. Magnesium is lost in significant amounts during the infiltration process; a plateau or arrest observed in the infiltration kinetics curves is attributed to Mg depletion at the infiltration front. At temperatures above 1050 °C, the beneficial effect of magnesium is diminished and the reactivation of infiltration in the final step is attributed only to the increase in temperature.