(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: 采用铜模喷铸与真空感应熔炼相结合，研究了Y含量(质量分数)对快冷Mg-6Al合金非平衡凝固组织及力学压缩性能的影响。通过稀土相结构及形貌分析对合金晶粒细化规律进行阐述。结果表明：铜模喷铸Mg-6Al合金组织显著细化，平均晶粒尺寸由铸态时的200 μm降低到24.5 μm，同时初生α-Mg相形貌从粗大不规则花瓣状向细小等轴枝晶转变。随Y含量增加，快冷Mg-6Al合金组织出现先细化后粗化趋势，其中添加1%Y时合金中形成方块状或棒状Mg24Y5相，能够促进异质形核，细化效果最佳，平均晶粒尺寸仅13 μm，相应压缩强度高达404 MPa。当Y含量过多时，快冷Mg-6Al-1.25Y合金中Mg24Y5相易发生团聚，从而弱化组织细化效果。
关键字: 稀土；镁合金；快速凝固；组织细化；异质形核
（National Defence Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:Effects of Y content on microstructure evolution and compression strength of rapidly cooled Mg-6Al alloy were investigated by injection casting into copper mould under the protection of vacuum induction melting. Both the structure and morphology of RE-rich phase were identified to reveal the refinement mechanism. The results show that the microstructure of rapidly cooled Mg-6Al alloy is significantly finer than that of the as-cast state, as indicated by the reduction of average grain size from 200 μm to 24.5 μm. Moreover, the grain morphology varies from coarse irregular petal to fine equiaxed dendrite. With the increase of Y content, the microstructure of rapidly cooled Mg-6Al alloy appears to be refined firstly and then coarsened. Square block or rod-shape Mg24Y5 phase forms in the ingot with the addition of 1%Y, which promotes heterogeneous nucleation of primary phase and is beneficial to grain refinement. Consequently, the minimum average grain size is merely 13 μm and the corresponding compression strength reaches 404 MPa. As for the sample with higher Y content, apparent agglomeration of Mg24Y5 phase occurs in Mg-6Al-1.25Y alloy, which weakens the grain refinement of rapid cooled alloy.
Key words: rare earth; magnesium alloy; rapid solidifcation; microstructure refinement; heterogeneous nucleation
