研究了微量Sr（0.01-0.1%，质量分数）对AZ91D镁合金枝晶生长和相析出的影响. 结果表明，加入微量Sr可明显细化AZ91D合金晶粒；随着添加量增加，初生相α-Mg枝晶逐渐球化，非平衡析出相β-Mg17A112增多；加入0.1% Sr后，在枝晶间β-Mg17A112相上依附析出针状或杆状Al4Sr新相. AZ91D合金凝固过程中Sr在固液界面前沿富集，并且优先在曲率较大的枝晶端面富集，抑止晶粒长大，从而增加允许形核时间，提高了形核数量，同时Sr的尖端富集降低了初生相α-Mg的尖端生长优势，球化了枝晶组织.
Effects of Sr addition on dendrite growth and phase precipitation of AZ91D alloy was studied. The experimental results showed that addition of 0.01-0.1wt%Sr to AZ91D alloy decreased the grain size obviously and promoted formation of globular grains. With the increase of Sr content the morphology of β-Mg17A112 phase in the alloy was changed and the amount of the phase increased. Meanwhile, the needle-like or pole-like Al4Sr phase adhering to the β-Mg17A112 phase at grain boundaries was observed. 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 results in the grain refinement and modification of α-Mg dendrite.
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