中文摘要
鎂合金具有高比強度、低比重、高傳熱性、無電磁性，同時具有高振動 減衰性及優良的電磁波干擾（EMI）防護等特性已廣泛的被應用於通訊、 電子及資訊等各類產品。其中筆記型電腦的主要結構（chassis）已有許 多也是以鎂合金為主要的材料。用於筆記型電腦主結構的鎂合金屬於薄 壁大平面的設計在製造上面臨許多困難，工業上目前常使用來生產鎂合 金薄壁件的方法則是壓鑄法（DieCasting）和半融溶射出成形居多。
為了解決鎂合金在壓鑄技術方面所面臨的困難，提升壓鑄件的良率，本 研究以模流分析軟體FLOW-3D為分析工具，以鎂合金薄壁鑄件為研究對象 ，探討鎂合金AZ91D在不同壓鑄條件下金屬熔液流動模式及凝固的現象， 並結合多澆口式扇形澆口澆流道系統模擬分析，預測並解決壓鑄件在充 填過程中可能發生的缺陷。以找出最佳化的壓鑄條件參數的組合。最佳 化的壓鑄條件為case16(100Mpa、110m/s、630℃、240℃），因其充填完 畢時固相率及溫度差皆較低使得在凝固過程中，模穴內金 液的凝固速率 可以十分的接近，避免冷卻速率不同與溫差過大所造成的熱變形及縮孔 。而經由充填過程順序的比較與壓力分佈、溫度分佈的模擬結果來判斷 ，扇形長度對寬度比值為1面積縮減率為30﹪時，可得較佳的壓鑄成品。
ABSTRACT
Magnesium alloys are metals which have high specific strength, low density and high thermal conductivity.They are non-magnetic materials with very good damping and EMI shielding capacities. These characteristics enable the magnesium alloys to be used in the communication, electronic devices and many other computer components. Among these applications, the chassis of notebook computer becomes one of the prominent usages in recent years. The chassis are usually thin-walled plate constructions, manufactured by die casting or semi- solid forming process which encounters many difficulties.In order to increase the yield of magnesium alloy in die casting, this study simulate the thin-walled plate in die casting process with a commercial code FLOW-3D, investigates the material flow in the die cavity, its solidification in the mold and their relations to defects of the products. The gate system effects on the results of the die casting products are also discussed. From the simulation, it is found that for AZ91D magnesium alloy, the best die casting parameter combination is: casting pressure 100 MPa, liquid flow speed 110 m/s, casting temperature 630℃ and mold temperature 240℃. This die casting condition promotes lower temperature variation in mold cavity,which in turn may lead to better yield.