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標題: 過 共 晶 Al-Si 合 金 之 快 速 凝 固 組 織 研 究
A Study on the Rapidly Solidification Structure of Hypereutectic Al-Si Alloy
作者: 魏伯州
關鍵字: Rapidly Solidification;快 速 凝 固
出版社: 材料工程學研究所
實驗結果顯示,電弧放電製程參數中,材料選用真空熔煉Al-Si合金重熔層(Remelted layer)孔洞數量明顯少於一般鑄造Al-Si合金;以去離子水(Distilled water)為絕緣液產生之重熔層厚度較煤油(Kerosene)大;峰值電流(Peak Current; Ip)越大,放電脈衝時間(Pulse Duration;τp)越長,電極極性(Polarity)為正,且在適當範圍內(15~45μsec)的放電休止時間(Pulse-off time;τr)時,可得到較大的重熔層厚度。
隨著熱處理溫度升高,重熔層內Si顆粒晶出有粗大化的現象;重熔層之硬度值隨熱處理溫度升高而有明顯的下降趨勢。重熔層之快速凝固組織為胞室結構(Cellular structure),晶胞室大小約200~400nm,晶胞與晶胞之的Si共晶胞界(Inter-cell Boundary)大小約10nm;在2000C-10hr熱處理條件下,重熔層內的晶胞中有Si顆粒晶出(約10nm)。重熔層經濕式蝕刻鋁後,以X光能量散譜儀(EDS)分析,發現共晶胞界組織為Si元素所組成。

This research is to obtain fine structures for hypereutectic AI-Si alloy by using Arc Electro Remeling Method. Since Si atoms are supersaturated in the solid solution due to rapid solidification, heat treatment processes were carried out in order to change the remelted structure. TEM, SEM as well as XRD were used to characterize the microstructure.
The experimental results show the Al-Si alloy which was melted and casted in vacuum contains less voids in the remelted layer, as compared to the remelted layer of the Al-Si alloy benig casted in air. The thickness of remelted layer depends on the characteristics of insulated solution, peak current(Ip), pulse duration(τp), electrode polarity as well as pulse-off time(τr). By selecting positive electrode polarity, longer τp and τr being in the range of 15~45μsec, a thicker remeled layer can be achieved.
Si phase will recrystallize from the remelted layer. The size of the Si particle become coarse with increasing heat treatment temperature. According to the TEM examination, solidification structure is cellular structure. The Cell's size is about 200~400nm. Inter-cell boundary size is about 10nm. Fine Si precipitates were observed in the specimen that was heat treated at 2000C for 10hr. When wet etching the remelted layer out of aluminum, we successfully obtain an Inter-cell boundary structure which is totally Si intercell network.
Appears in Collections:材料科學與工程學系

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