合金成分与制备工艺对Nd-Fe-B铸片显微组织的影响

Effects of composition and preparation process on the microstructure of Nd-Fe-B strip cast alloys

在工业生产线上，选择不同条件下制备的Nd．Fe．B合金铸片，分析了成分设计、浇注工艺以及铸片厚度对Nd-Fe-B合金铸片显微组织的影响。成分设计中较高的重稀土元素含量增大熔液结晶时的过冷度，使铸片显微组织中产生较多细小等轴晶。当平均厚度为0．3～0．4mm时，铸片具有较好的显微组织，即主相以片状晶方式沿垂直贴辊面的方向生长，富Nd相呈薄层状均匀分布在主相内部及晶界处，薄层间距约为3-5μm；厚度偏大时，在铸片自由面附近存在少量α-Fe相，而厚度偏小时，其显微组织中富Nd相薄层间距偏小，仅为2μm左右。合适的浇注工艺可以获得理想的铸片显微组织，浇注温度偏低导致细小等轴晶出现，而且浇注温度偏低和熔液浇注速度偏慢均不利于片状晶生长。

Nd-Fe-B strip cast alloys were prepared under different conditions in industrial production line. The effects of heavy rare earth element content, pouring process and thickness on the microstructure of Nd-Fe-B strip cast alloys were analyzed. A higher heavy rare earth element content in the alloy composition increases the supercooling degree of alloy melt crystallization, resulting in the formation of many over-small equiaxial grains. The strip cast alloys with an average thickness of 0.3-0.4ram have a good microstructure with lamellar main Nd2Fel4B phase growing along the direction perpendicular to the wheel surface, and the Nd-rich phase with a interlamellar spacing of 3-5pro evenly distributing in the main phases and grain boundary. A small amount of ct-Fe exists near the free surface of strip cast alloys with bigger average thickness. However, the interlamellar spacing of Nd-rich phase is only about 2pm for strip cast alloys with smaller average thickness. The strip cast alloys with desired microstructure can be prepared using appropriate pouring process. Too low melt pouring temperature leads to formation of many over-small equiaxial grains, and both lower melt pouring temperature and slower melt-pouring speed inhibites the growth of lamellar grains.