The influences of superheating, cooling rate, repetitive melting and solidification cycles, and addition of some types of oxides on the undercooling of zone refined aluminum were studied. A 20 grams sample of molten aluminum was first passed through a graphite filter in order to remove oxide films from the sample and then remelted and solidified in an extra high grade graphite crucible under vacuum conditions. The larger the degree of superheating of the sample, the larger is the degree of undercooling. The maximum degree of undercooling is 82K. When the sample is superheated by 300K above the melting point, no undercooling occurrs. Larger undercooling is obtained through air-cooling than through furnace-cooling. Further, while the addition of SiO2 powders eliminates undercooling in the sample, the addition of Al2O3 powders does not affect the degree of undercooling.
