Grain refinement during solidification of Mg-4Y-0.5Zr (wt.%) alloy was both experimentally and numerically studied. A two-dimensional cellular automaton model is adopted. A LGK (Lipton–Glicksman–Kurz) analytical model is solved to predict the variation of dendrite tip velocity with undercooling under the conditions with and without Zr. With addition of 0.5 Zr, the growth velocity of dendrite tip is approximately one sixth of that without Zr. Experimental characterizations showed that the addition of Zr resulted in a significant grain refinement. The effects of cooling rate, initial nucleation density and Zr addition were numerically examined. A high cooling rate is important to the grain refinement, because it effectively increases the degree of effective undercooling and nullifies the effect of latent heat on stopping the heterogeneous nucleation. For Mg-4Y alloy, solute suppressed nucleation is magnified with the increase in initial nuclei density. Since a large portion of nuclei is depressed due to the fast overlap of solute diffusion layers, the grain refinement is not as desirable as expected. The mechanism of grain refinement with addition of Zr is that a reduced growth rate is accompanied with a slowed release rate of latent heat. Without much temperature interference from the neighboring developing dendrites, more nuclei can achieve enough undercooling for nucleation and become grains. A high cooling rate promotes multi-step nucleation and significantly refines the grain structure, which cannot be achieved at a low cooling rate.

Mg-4Y-0.5Zr (wt.%) 合金凝固过程中的晶粒细化进行了实验和数值研究。采用二维元胞自动机模型。解决了 LGK（Lipton-Glicksman-Kurz）分析模型，以预测在有和没有 Zr 的条件下枝晶尖端速度随过冷的变化。添加0.5 Zr后，枝晶尖端的生长速度约为无Zr的六分之一。实验表征表明，添加 Zr 导致显着的晶粒细化。数值研究了冷却速率、初始成核密度和 Zr 添加量的影响。高冷却速度对晶粒细化很重要，因为它有效地增加了有效过冷度并抵消了潜热对停止异相形核的影响。对于Mg-4Y合金，随着初始核密度的增加，溶质抑制形核被放大。由于溶质扩散层的快速重叠，大部分晶核被压低，晶粒细化并不如预期的那样理想。添加 Zr 的晶粒细化机制是生长速率降低伴随着潜热释放速率减慢。在没有来自相邻发展枝晶的太多温度干扰的情况下，更多的晶核可以达到足够的过冷度以进行成核并成为晶粒。高冷却速度促进多步形核并显着细化晶粒结构，这是低冷却速度无法实现的。由于溶质扩散层的快速重叠，大部分晶核被压低，晶粒细化并不如预期的那样理想。添加 Zr 的晶粒细化机制是生长速率降低伴随着潜热释放速率减慢。在没有来自相邻发展枝晶的太多温度干扰的情况下，更多的晶核可以获得足够的过冷度以进行成核并成为晶粒。高冷却速度促进多步形核并显着细化晶粒结构，这是低冷却速度无法实现的。由于溶质扩散层的快速重叠，大部分晶核被压低，晶粒细化并不如预期的那样理想。添加 Zr 的晶粒细化机制是生长速率降低伴随着潜热释放速率减慢。在没有来自相邻发展枝晶的太多温度干扰的情况下，更多的晶核可以获得足够的过冷度以进行成核并成为晶粒。高冷却速度促进多步形核并显着细化晶粒结构，这是低冷却速度无法实现的。在没有来自相邻发展枝晶的太多温度干扰的情况下，更多的晶核可以达到足够的过冷度以进行成核并成为晶粒。高冷却速度促进多步形核并显着细化晶粒结构，这是低冷却速度无法实现的。在没有来自相邻发展枝晶的太多温度干扰的情况下，更多的晶核可以获得足够的过冷度以进行成核并成为晶粒。高冷却速度促进多步形核并显着细化晶粒结构，这是低冷却速度无法实现的。