凝固為相當重要之材料製程技術。材料的微觀組織會在凝固過程，決定各項性質之優劣，故凝固學為重要的研究領域。
方向性凝固，又稱定向凝固，對於金屬材料，就是人為地控制融熔金屬的結晶生長方向，以獲得結晶方向相近的柱狀晶，甚至單晶結構的凝固方法。電磁凝固是以電場或磁場控制凝固過程，為較新的研究領域。
本研究以錫-鉛合金不同濃度及磁場為研究材料，錫-鉛合金系統是典型的共晶系統，共晶系統中，加入另一成分金屬，熔點會降低，液相線經過最低溫度點成為共晶點。
鉛的濃度越高時，晶粒尺寸小，鉛的濃度越低，晶粒尺寸大。施加線性相斥磁場，中間的部分晶粒尺寸小，邊緣的部分晶粒尺寸大。施加線性相吸磁場，中間的部分晶粒尺寸大，邊緣的部分晶粒尺寸小。
本研究主要之研究方法有巨觀金相組織與微觀金相組織觀察。根據實驗結果，在不同磁場作用與濃度下凝固確實會影響材料的微結構。

Solidification is an important technique in material manufacturing. Solidification affects the morphology control of microstructures, which directly influence all properties.
The directional solidification process enables grain orientation to put in order along a specific direction. This process would decrease grain boundary (G.B.), which could improve mechanical properties of materials.The electromagnetic solidification process means the solidification process with the magnetic field or electric fields.
In our study of directional solidification, lead-tin alloy is used as the casting material with different initial concentrations and magnetic fields. To analyse the solidification processes, we used metallographic observation, including macrostructure, microstructure, and calculate average grain size. The metallographic procedures are cutting specimen, specimen mounting, abrasive grinding, polishing, etching and microscopy. We observe macrostructure by eyes and ruler, observe the microstructure by optical microscope, and calculate the average grain size in lateral morphology.
We find that when the concentration of lead is smaller, the grain boundary is more difficult to observe. The bottom of casting sample is the chill zone. The middle of casting sample is the columnar zone. The top of casting sample is the air-affected zone. Each case has different sizes in three regions with different concentrations of lead and magnetic fields. Chill zone are small equiaxed grains. Columnar zone are columnar grains. Air-affected zone are large equiaxed grains. When we put magnet attraction in linear magnetic field, we can find out large grain size in the middle,small grain size in the edge. When we put magnet repulsion in linear magnetic field, we can find out small grain size in the middle, large grain size in the edge. According to the experimental results, the concentration of lead and the magnetic field actually influences the material microstructures of directional solidification.

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