電流對鉛錫共晶合金凝固組織影響之研究

Abstract

改善鑄件凝固組織一直是大家努力的目標。本實驗嗜試於鉛錫共晶合金凝 固過程中，直接通以各種不同電流密度之直流電源(5V,400-4000mA/cm2), 來觀察電流對鉛錫共晶合金凝固組織的影響。利用熱分析的方法，量測鑄 件凝固冷卻曲線，由過冷度、再輝速率、凝固時間、及固相率變化等方面 實驗結果發現，通電流可改變鑄件之凝固組織。通電流後可降低鉛錫共晶 合金凝固前過冷度的大小，而改善重力偏析的情形，使得成份分佈較均勻 。在1200 mA/cm2電流密度下，過冷度5.9℃最小，其成分最為均勻。使用 直接通電流的方式較傳統改善鑄件的方法方便許多。 The purpose of this research is to improve the microstructure of castings by trying a new method. To study the effect of electric current density on the microstructure of the casting, we used different electric current density (5V, 400-4000 mA/ cm2, D.C.) through the casting during solidification process of Pb-Sn eutectic alloy. We measured the cooling curve of the Pb- Sn alloy to find the undercooling , the rate of recalescence, solidification time and the variation of solid fraction. The results showed that the electric current through the solidification process of Pb-Sn eutectic alloy could modify the microstructure of the alloy. The electric current could reduce the gravity segregation because of reducing the undercooling before solidification. In this study, the optimum condition is under 1200 mA/cm2 electric current density, which can obtain the least gravity segregation . It is a convenient method to modify the microstructure of the casting by passing electric current.