(1. 南昌航空大学 江西省金属材料微结构调控重点实验室，南昌 330063；
2. 南昌航空大学 轻合金加工科学与技术国防重点学科实验室，南昌 330063)
摘 要: 采用真空感应熔炼与阶梯铜模喷铸相结合，制备出微米/纳米SiC参与下快冷镁合金，研究SiC尺寸对非平衡凝固镁合金异质形核及组织细化的影响。结果表明：冷速的提高与SiC的添加共同促进镁合金的复合细化，其中铜模喷铸条件下微米SiC的细化效果更佳。当铜模内径di=4 mm，添加2%的微米SiC(质量分数)后快冷镁合金平均晶粒尺寸减小到5 μm以内。经(400 ℃, 2 h)等温固溶处理后，快冷合金晶界处的离异共晶β-Mg17Al12相消失，初生α-Mg晶粒由细小蔷薇状向多边形组织发生转变。通过枝晶生长与溶质截留模型的理论计算，铜模喷铸条件下获得的过冷度范围为67~80 K，所对应的临界形核半径为0.115~0.116 μm，因此，更有利于微米SiC对镁合金的组织细化。
关键字: 非平衡凝固；异质形核；枝晶生长；组织细化；镁合金
（1. Key Laboratory for Microstructural Control of Metallic Materials of Jiangxi Province, Nanchang Hangkong University, Nanchang 330063, China;
2. National Defence Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:With the combination of vacuum induction melting and spray casting by step copper mould, rapid cooled magnesium alloys containing micro/nano SiC were fabricated, and then the influence of particle size of SiC on heterogeneous nucleation and microstructure refinement was investigated. The results show that both the increase of cooling rate and the addition of SiC promote grain refinement of magnesium alloy, whereas, the effect of SiC with micron size is better than that with nano under spray casting condition. As for the copper mould with inner diameter di=4 mm, the addition of 2% micron SiC generates the reduction of average grain size within 5 μm. After solid solution treatment at 400 ℃ for 2 h, the grain morphology of primary α-Mg phase transits from fine rosette to polygon, accompanied by the disappearance of divorced eutectic β-Mg17Al12 phase at grain boundary. According to the theoretical calculation of dendrite growth and solute trapping model, the obtained undercooling range for spray casting is 67-80 K，which corresponds to the critical nucleation radius with 0.115-0.116 μm. Consequently, SiC particle with micron size is advantageous for microstructure refinement.
Key words: non-equilibrium solidification; heterogeneous nucleation; dendrite growth; microstructure refinement; magnesium alloy
