(华南理工大学 材料科学与工程学院，广州 510640)
摘 要: 利用Mg-20%Sb中间合金对过共晶Mg-4.8%Si合金进行变质处理，考察Sb的含量对Mg2Si初晶变质效果(主要包括形态和尺寸)的影响规律，并讨论其变质机制。结果表明：Sb的加入量是决定其能否有效变质过共晶Mg-4.8%Si合金中Mg2Si初晶的重要因素；在未变质的过共晶Mg-Si合金中，Mg2Si初晶以粗大的树枝晶状为主；当Sb加入量低于0.8%(质量分数)时，Mg2Si初晶形态无明显改善，其平均尺寸略有降低；当Sb加入量达到并超过1.2%后，Sb才能有效变质过共晶Mg-4.8%Si合金中Mg2Si初晶，且Mg2Si初晶呈细小的颗粒状弥散分布，其平均尺寸迅速减小；其变质机制应与残留在熔体中弥散分布的Mg3Sb2粒子作为Mg2Si初晶的形核核心有关。
关键字: 过共晶Mg-Si合金；Sb；变质；Mg2Si初晶
（School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China）
Abstract:The hypereutectic Mg-4.8%Si alloy was modified by using Mg-20%Sb master alloy. The effect of Sb addition on the modification of primary Mg2Si crystals and its modification mechanism were investigated. The results show that the Sb content is a significant factor that determines the modification effect of primary Mg2Si crystals. The primary Mg2Si crystals are mainly coarse dendritic for the unmodified hypereutectic Mg-4.8%Si alloy. The morphologies of primary Mg2Si crystals can not be effectively modified by Sb under the condition of Sb content less than 0.8%. The average sizes of primary Mg2Si crystals slightly decrease. With the Sb addition increasing to 1.2%, the primary Mg2Si crystals are effectively modified into small particles, which distribute uniformly. Compared with the unmodified hypereutectic Mg-4.8%Si alloy, the average sizes of the primary Mg2Si crystals for the modified Mg-4.8%Si alloy by 1.2%Sb addition drastically decrease. The modification mechanism should be associated with the Mg3Sb2 particles remained in the hypereutectic Mg-4.8%Si meld modified by Mg-20%Sb master alloy. The Mg3Sb2 particles should act as nucleating substrates of the primary Mg2Si crystals during solidification.
Key words: hypereutectic Mg-Si alloy; Sb; modification; primary Mg2Si crystal
