A356鋁合金鑄件有適當的強度，且可以鑄造複雜的鑄件，因此被廣泛的用於工業上。但由於鋁合金鑄件容易造成微縮孔的缺陷使得機械性質變差。本實驗研究晶粒細化對縮孔形成的影響，並與孔洞的生成理論比較。
實驗利用SKD61工具鋼金屬模鑄造25Φ×150L㎜試棒。將已調配好成分(無添加Ti及添加0.15%Ti)的A356鋁合金鋁錠熔融鑄造，控制模溫、固定鋁湯的初始氫含量，並以HP溫度量測器量測凝固時的溫度變化，以獲得實驗所需的熱參數。
實驗結果顯示，晶粒細化使鑄件的孔隙率減小，此減小的原因，主要是由於孔洞平均半徑減小。由理論推導孔洞半徑受到鑄件晶粒大小、凝固時間、金屬液中之氣孔壓力的影響；添加Ti的鑄件，具有較小的晶粒大小及較短的凝固時間，預測其孔洞半徑小於無添加Ti鑄件。此預測符合實驗。
孔洞平均距離越短反映孔洞數量越多。實驗結果顯示，添加Ti的鑄件其孔洞平均距離較短，因此Ti的添加使鑄件的孔洞數量上升。
添加Ti使孔洞的平均半徑減小，孔洞平均距離減小。而孔洞平均半徑減小是造成Ti鑄件孔隙率下降的主因，本研究顯示孔洞的生成理論對於鑄件孔隙率之預測，大致與實驗相符。

A356 aluminum alloy are being widely applied in the industry due to the material’s good castability and mechanical properties. However, the mechanical properties can be degraded by the formation of porosity. Grain refinement is considered as a required treatment to upgrade the mechanical properties of the alloy. In this study, we investigate the effect of grain refinement on the distribution of porosity in a permanent mold casting.
SKD61 permanent mold was used to cast 25Φ×150L㎜ sample. In the experiment, the mold temperature and the hydrogen content in the melt were fixed. Thermal measurements were used to obtain the thermal variables in the casting.
Grain refiner was found to reduce the porosity of A356 casting from the result of experiment. In the grain-refined condition, rp varies with Pg, grain size, and local solidification time. Because of the smaller grain size in the grain-refined condition, rp was found smaller than that in the non grain-refined condition.
The result of the experiment shows that there is a small re is smaller in the grain-refined condition. However, the reduced of porosity content is mainly due to the decrease of rp in the grain-refined condition. In this study, the prediction of porosity content by theoretical analysis generally agrees with the experiment.

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