Modification of Solidification Structures by Pulse Electric Discharging

A new process using pulse electric discharging for modification of solidification structures was investigated. If an extremely high voltage or high current is applied to solidifying metallic alloys by discharging a capacitor bank, large pressure gradients result, which produce strong local shear, and can be expected to significantly modify structures. Experiments were conducted on Sn-15wt%Pb alloy and the appropriate conditions to modify solidification structures were examined, including cooling rate, initial capacitor bank voltage, and time to discharge after onset of solidification. Solidification structures were modified from dendritic to globular (with fine grain size) under appropriate operating conditions. The critical conditions to attain the globular structures in these experiments can be expressed in terms of initial capacitor bank voltage and the fraction solid when discharging was carried out.