Guan Tianyang, Zhang Zhifeng, Bai Yuelong, Li Bao, Wang Ping
General Research Institute for Non-Ferrous Metals, No.2, Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, No. 3-11, Wenhua Road, Shenyang 110004, China.
Materials (Basel). 2019 Jul 23;12(14):2337. doi: 10.3390/ma12142337.
There are two critical stages of grain refinement during solidification: above and below the liquidus temperature. The key to improve the refinement potential is ensuring the nucleation sites precipitate in large quantities and dispersed in the melt above liquidus. In this work, internal cooling with annular electromagnetic stirring was applied to an Al-Zn-Mg-Cu-Zr alloy at a temperature above liquidus. A systematic experimental study on the grain refining potential was performed by combining different melt treatments and pouring temperatures. The results indicate that internal cooling with annular electromagnetic stirring (IC-AEMS) had a significantly superior grain refining potency for the alloy compared to traditional electromagnetic stirring (EMS). In addition, homogeneous and refined grains were achieved at high pouring temperatures with IC-AEMS. The possible mechanisms for the enhanced grain refinement above the liquidus temperature are explained as the stable chilling layer around the cooling rod in IC-AEMS providing undercooling for the precipitation of AlZr nucleant particles and the high cooling rate restraining the growth rate of these particles. At the same time, forced convection promotes a more homogeneous distribution of nucleant particles.
液相线温度以上和以下。提高细化潜力的关键是确保形核位点在液相线以上大量析出并分散在熔体中。在这项工作中，对一种Al-Zn-Mg-Cu-Zr合金在液相线以上的温度下采用环形电磁搅拌进行内部冷却。通过结合不同的熔体处理和浇注温度，对晶粒细化潜力进行了系统的实验研究。结果表明，与传统电磁搅拌（EMS）相比，环形电磁搅拌内部冷却（IC-AEMS）对该合金具有显著优越的晶粒细化能力。此外，采用IC-AEMS在高浇注温度下可获得均匀细化的晶粒。液相线温度以上晶粒细化增强的可能机制解释为，IC-AEMS中冷却棒周围稳定的激冷层为AlZr形核颗粒的析出提供过冷度，且高冷却速率抑制了这些颗粒的生长速率。同时，强制对流促进了形核颗粒更均匀的分布。
