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Mg_2Si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Mg_2Si初晶的重要因素;在未变质的过共晶Mg-Si合金中,Mg_2Si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,Mg_2Si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Mg_2Si初晶,且Mg_2Si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Mg_3Sb_2粒子作为Mg_2Si初晶的形核核心有关.
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 Mg_2Si 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 Mg_2Si crystals. The primary Mg_2Si crystals are mainly coarse dendritic for the unmodified hypereutectic Mg-4.8%Si alloy. The morphologies of primary Mg_2Si crystals can not be effectively modified by Sb under the condition of Sb content less than 0.8%. The average sizes of primary Mg_2Si crystals slightly decrease. With the Sb addition increasing to 1.2%, the primary Mg_2Si 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 Mg_2Si crystals for the modified Mg-4.8%Si alloy by 1.2%Sb addition drastically decrease. The modification mechanism should be associated with the Mg_3Sb_2 particles remained in the hypereutectic Mg-4.8%Si meld modified by Mg-20%Sb master alloy. The Mg_3Sb_2 particles should act as nucleating substrates of the primary Mg_2Si crystals during solidification.
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