鑄造在工業史中的應用可追朔至數千年前，為一歷史悠久、發展純熟的製程技術。依加工材料的不同，因應發展出不同的鑄造方法和模具，可用於大量製造，也能處理表面複雜的精密模型。隨著技術的進步，對鑄件品質與製程條件的要求越來越高，在金屬凝固過程中溫度場與濃度場即為影響鑄件品質的重要關鍵。一般鑄造模式不易控制其凝固結構之型態，而使用方向性凝固所產生之微結構則可沿著固定方向成長，並控制晶粒大小，提高材料之機械性質與物理特性。
針對方向性凝固，本研究使用錫鉛合金(Sn-15wt%.Pb、Sn-20wt%.Pb
、Sn-37wt%.Pb)為材料，透過不同的實驗參數與鑄造方法，探討凝固模式對於微結構之影響。並觀察微觀(Microscopic)顯微組織及巨觀(Macroscopic)顯微組織，比較其優選方向控制情形、晶粒尺寸與型態、晶體成長的束縛控制和溫度梯度、成長速率之間的關係。
由不同濃度之實驗結果可得知，晶體成核與成長過程主要受溫度梯度所控制，且晶體的成長型態與大小和合金成分有密切的關係，透過此研究分析結果，可對於方向性凝固之控制機制有更進一步的掌握。

Foundry engineering has been widely applied in industrial manufacturing for hundred years. Especially for the casting technology, it still leaves a lot to be concerned. To improve the mechanical properties of the metal materials, directional solidification is recommended for controlling the grain morphology and the microstructure.

In this study, tin-lead alloy is used as the casting material in directional solidification and sand casting experiments while the alloy concentration and cooling media are set to be the independent variables of different experiment groups. The solidified macrostructure and microstructure including the grain size, equiaxed zones and columnar areas are investigated among the different experimental parameters. Furthermore, the transient temperature field and the growth rates of the grains are also analyzed from the experimental data to discuss their effects on the directional solidification process.

The result shows that the nucleation and growing process of grains are controlled by the temperature gradient while the grain morphology and size are closely associated with the concentration fields of the alloy. In other words, the macrostructure and microstructure of the castings are affected by the experiment temperature, cooling chills, casting molds and the initial concentration of the alloy. The differences of the solidified structures among the experiment groups can be observed by eyes or through the optical microscope,

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