(1. 上海交通大学 材料科学与工程学院，
上海 200030；
2. 南通工学院 机械工程系，南通 226007)
摘 要: 将含有稀土的熔剂JDN-Ⅰ用于覆盖处理A356合金。实验结果表明，该稀土熔剂对A356合金的二次枝晶臂间距dDAS值有着较大的影响。无熔剂覆盖时，水淬获得的dDAS值比空冷下降30.8%；有JDN-Ⅰ熔剂覆盖时，水淬获得的dDAS值比空冷下降88.2%；水淬时，有熔剂覆盖的dDAS 值比无熔剂覆盖低77.7％；空冷时，有熔剂覆盖的dDAS 值比无熔剂覆盖高23.3％。分析认为，存在2个临界冷速v1和v2：当冷速v<v1时，dDAS值由液相线斜率决定；当v>v2时，dDAS值由JDN-Ⅰ熔剂中的稀土含量决定；当v1＜v＜v2时，dDAS值由凝固时间稀土含量和液相线斜率三者共同决定。
关键字: 稀土熔剂；A356合金；二次枝晶臂间距
secondary dendrite arm spacing
of A356 alloy
（1. School of Materials Science and Engineering，
Shanghai Jiaotong University， Shanghai 200030， China;
2. Department of Mechanical Engineering，
Nantong Institute of Technology，Nantong 226007，China）
Abstract:A rare earth flux—JDN-Ⅰ was used for A356 alloys by covering on the surface of the melt. The experimental results indicate that the rare earth flux affects the secondary dendritic arm spacing (dDAS) of A356 alloy. The dDAS obtained by water-quenching decreases by 30.8% in comparison with that by air-cooling without the covering of the flux，while the dDAS obtained by water-quenching decreases by 88.2% in comparison with that by air cooling with the covering of JDN-Ⅰ flux. It is suggested that there are two critical cooling rates，v1 and v2. If the cooling rate v<v1，the dDAS is primarily determined by slope of liquidus(/M/) which is determined by the compositions， diffusion coefficient of the alloy. If v>v2，the dDAS is determined by the ［RE］ of JDN-Ⅰ flux and solidification time tf. If v1＜v＜v2，the dDAS is determined by tf ，[RE］ and M together.
Key words: rare earth flux; A356 alloy; secondary dendritic arm spacing
