| It is proved by experiments that electric pulse has an effect on solidification structure of alloy, but till now it has no consistent view about solidification reason, which impedes the application of electric impulse technique. In order to reveal the modification mechanism of electric pulse deeply, electric pulse's effect on Pb-Sn alloy molten structure is discussed in this dissertation in terms of Calorimetry(DSC), solidifying texture and activity.Experiments show that solidification structure has been dramatically refined with the treatment of pulse electric field and current. The number of grains in pulse current is increased by 1.6, while the number in pulse field is 1.4. By means of DSC technique, variation of solidifying point of Pb-Sn alloy is studied under pulse electric field and current. It is observed that the freezing point of Pb-Sn alloy is reduced in a various degree. This phenomenon is explained through classical nucleation theory. The mixing enthalpy of Pb-Sn alloy has been calculated based on Miedema Model. Through thermodynamic relations, other thermodynamic functions such as excess Gibbs energy, excess entropy and activity have also been deduced. Based on cluster structure assumption of liquid metal, the model of Pb-Sn liquid structure is established and electric pulse's effect on molten is evaluated by the model. The component's activity is correlated to the coefficient of distribution, so measuring the coefficient of distribution is important to understand the activity. Pb and Zn are not dissolved absolutely and mutually, so they are selected as parent phases to study distribution law of Sn in Pb and Zn. Results show that electric pulse can change partition coefficient, which further proves the modification effect of electric pulse.Liquid is the parent phase of solid state. Liquid structure has a direct impact on solidification structure. Electric pulse can modify molten structure, thus lead to alternation of component's activity in the alloy system, so activity may be a macro-parameter by measuring change of molten structure. |
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