中文摘要：

　加入微量Sr（0．01％～0．1％，质量分数）可明显细化AZ91D镁合金晶粒，随Sr含量增加，初生相α—Mg尺寸逐渐减小，而二次枝晶间距变化不大，同时β—Mg17Al12析出相增多．Sr添加量为0．1％时，针状或块状Al4Sr相依附在枝晶间的β—Mg17Al12相上析出．Sr在AZ91D合金凝固固-液界面前沿富集，并且优先在曲率较大的枝晶端面富集，从而抑制晶粒长大，细化了合金中初生相α—Mg；同时，Sr在枝晶的尖端富集降低了初生相α-Mg的尖端生长优势，改变了初生相形貌．

英文摘要：

The addition of 0.01%-0.1%Sr （mass fraction） to AZ91D alloy decreased the grain size obviously and changed the morphology of the primary phase α-Mg. With the increase of Sr content the morphology ofβ-Mg17Al12 phase in the alloy was changed and its amount increased. Meanwhile, the needle-like or block-like Al4Sr phase adhering to theβ-Mg17Al12 phase distributes among interdendrities. The enrichment of Sr element at solidification interface front, especially at the tip of α-Mg dendrite, restricts the growth of α-Mg dendrite and changes the preferential growth of α-Mg, which resulted in the grain refinement and the blunting of α-Mg dendrite.