Molten Al-12%Si alloys modified with Sr 0.05%, Ba 0.05%, Ca 0.1%, Mg 0.1%, Sb 0.2% and Sr 0.05%+ Be 0.004% were held up to 6hrs and cast in a permanent mold. The alloys Sr, Ba and Ca-modified have an incubation period of modification effect, but ones Mg and Sb-modified don't have. The modification effect of Sr is weak just after Sr introducing and attains a maximum after holding for 2hrs. When P 0.001% is introduced to the melt in which Sr modification effect attains its maximum, the effect once lowers to the level just after Sr addition and attains the maximum again after holding for 2hrs. The incubation period is a period for a neutralizing reaction of aluminum phosphide, nucleus of Si, to another phosphides such as Sr phosphide.
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