鑄態鎂鋁合金鑄件微結構的研究與發展，取決於鑄造人員的知識與能力，目前關於鎂合金鑄態凝固過程和其微結構的完整資料較少，因此，本研究的目標係建立鎂鋁合金於凝固過程的製程參數與描繪相關之微結構。 本研究主要利用CA-CCA(computer aided – cooling curve analysis)與金相量化分析(quantitative metallography analysis)探討鎂鋁合金於凝固過程之行為，使用的材料有商用鎂鋁合金AZ91與本實驗利用純鎂(3N)與純鋁(3N)調配之鎂鋁合金：Mg-3Al, Mg-6Al, Mg-9Al and Mg-15Al，微結構則使用光學顯微鏡、掃描式電子顯微鏡與EDS line scan 觀察與辨別各種不同析出相的形態與成分。 本實驗的冷卻速率範圍約為10-40 ，冷卻速率提高使得鎂鋁合金之鋁的固溶度降低，造成二次相(Mg17Al12)析出比率減少，金相量化分析顯示冷卻速率越快而析出物尺寸與析出比率越低，金相量化分析也可定義二次相(Mg17Al12)存在的臨界尺寸。藉此研究應可提供未來鑄態鎂鋁合金相關之製程參數與參考資料庫。 Research and development of magnesium casting alloy depends largely on the metallurgist’s understanding and ability to control the microstructure of the as-cast part. Currently few sources of magnesium solidification information and as-cast microstructure exist. Therefore, the purpose of this research is to create the general database of magnesium solidification behavior and to characterize the resultant microstructures. Experiment has been development and constructed to study the solidification behavior of magnesium-aluminum alloy casting alloys via CA-CCA(computer aided – cooling curve analysis) and quantitative metallography analysis. These analyses have been performed on five kinds of magnesium-aluminum alloys, including commercial AZ91 magnesium alloy, and experimental alloys which was mixed with pure magnesium (3N) and pure aluminum (3N) such as Mg-3Al, Mg-6Al, Mg-9Al and Mg-15Al. The resultant microstructure has been characterized for microstructures and the various phases were analyzed using optical and scanning electron microscopy, as well as energy dispersive x-ray spectroscopy. The measurement were performed using a cooling rate on the order 10-40 , and results of these analyses show the higher cooling rate, the lower volume fraction of Mg17Al12 precipitation, and this is because the solid solution of Al in Mg-Al is controlled by cooling rate. Quantitative metallography analysis reveals the relationship between cooling rate and as-cast microstructure. It also can be used to define critical conditions for existing partially divorced and fully divorced precipitation. Finally, these results should provide useful knowledge for research towards develop casting procedure of magnesium alloys.
