本實驗試以電弧放電於AC8A鋁合金表面進行重熔，針對由電弧放電產生重熔層的優劣性(依氣孔的多寡及重熔層的均勻度判斷)下探討，因此如何在實驗中以不同的加工參數及絕緣液得到較佳重熔層為首要工作；重熔層再以時效處理來加以提升其機械性質，以最傳統及步驟簡單的方式來加以解決。 實驗結果得知最佳參數為低壓電流(AP) 21A、on time放電參數(PA) 400µs、off time放電休止參數(PB) 4及間隙電壓參數(GA) 50V。在絕緣液選擇方面為去離子水，電極極性為正。經適當的加工參數可以得到氣孔數少且平均厚度約100µm的重熔層；重熔層在未經任何時效時，結果顯示其平均硬度值Hv 138.43比經過時效處理的鋁基地還高，強化型式主要以固溶強化為主。將重熔層進行時效處理(溫度在170℃時間為7小時)得到一最大平均硬度值Hv 168.25，由TEM中發現重熔層內存在cell結構及微小析出物，分別造成晶胞界強化及析出硬化的效果。 AC8A鋁合金可藉由電弧重熔於表面形成重熔層，結果顯示重熔層可藉由不同的強化機構提升硬度值，不同強化機構正是提升重熔層硬度的主要原因。 The process of surface remelting for AC8A Al-Si-Ni-Mg alloy by arc remelting method and the characterization of the remelted layer were in-vestigated. The number of voids in remelted region and the uniformity of the layer strongly depend on experimental working parameters such as peak current, pulse duration and pulse-off time, etc. Two insulations kerosene, distilled water were used in this study. Aging treatments were performed, focusing on the improvement of hardness for remelting layer. The experimental results show that the AC8A alloy which was melted and casted in vacuum contains a little less voids in the remelted layer, as compared to the layer of the alloy being casted in air. Hence, vacuum casting process, which can apparently reduce the hydrogen con-tent in AC8A, does not have significant effect on voids reduction in remelted layer. In this work, by using suitable working parameters such as peak current 21A, pulse duration 400s, pulse-off time 15s and main power supply voltage 50V, the number of voids in the remelted layer can be reduced to a much lower limit. Aging treatment performed at 170oC for 10 hours can effectively improve the hardness of remelted layer from Hv 138 to Hv 168, though the hardness of AC8A substrate has only Hv 90. Results of TEM examinations show cell structure is very fine with cell size about 100~200nm. After aging, nano-size precipitates distrib-uting in the interior of cells as well as in the cell boundary were observed. The precipitation which occurs not only in cell but cell boundary causes the hardness of remelted layer increased.