优化主合金铸片结构制备高性能烧结钕铁硼磁体

Preparation of High Performance Sintering Nd-Fe-B Magnet by Optimizing Strip Cast Microstructure of Master Alloy

在工业化生产线上采用双合金法，通过优化主合金铸片结构制备了最大磁能积415kJ·m^-3，内禀矫顽力1027kA·m^-1的高性能烧结钕铁硼磁体，磁体具有高抗腐蚀性，在121℃，0．27MPa，相对湿度100％的环境中，经过168h后磁体单位面积失重为2．08mg·cm^-2。重点研究了主合金铸片结构对磁体组织及性能影响：由于稀土含量低，采用一般速凝工艺时主合金Nd28．0Fe70Co1.0B1．0铸片的自由面附近出现大量树枝状α-Fe，最终制备的磁体中存在大尺寸富Nd团聚，晶粒边界不平整，磁体密度较低为7．45g·cm^-3矫顽力只有870kA·m^-1；通过改进速凝工艺，Nd280Fe70C01．0B㈨铸片结构优化，铸片中α-Fe相析出基本被抑制，柱状晶厚度为3—4，连续生长。最终制备磁体富Nd相团聚减少，晶粒边界平直、光滑。最终制备的磁体密度提高到7．57g·cm^-3，矫顽力大幅提升到1027kA·m^-1。

The high performance sintering Nd-Fe-B magnet with intrinsic coercivity 1027 kA -m ^-3 and maximum energy product 415 kJ .m^-3 was prepared by a binary powder blending technique on the industrialization product line. The magnet had strong corrosion resistance; the mass loss of the magnet was only 2.08 mg.cm^-2 after 168 h under the condition of 121 ℃, 0.27 MPa and 100% relative humidity. The effects of main alloy strip structure on sintering magnet microstructure and magnetic performance were investigated. Owing to the low rare earth concentration of the master alloy, there were a lot of α-Fe phases near the free surface of Nd25.0FeToC1.0B1.0 strip cast flakes, subsequently the magnet had much aggregation of Nd-rich phase, the grain boundary was unsmooth, and then the magnet had low density of 7.45 g.cm^-3, the coercivity was only 870 kA.m^-1 After optimizing the strip cast flakes structure, the α-Fe phases in the strip cast flakes were suppressed and Nd2Fe14B columnar grains of about 3 -4 μm were formed along the solidification direction. There was less aggregation of Nd-rich phase in the magnet, the distribution of Nd-rich phase was uniformity and the grain boundary was straight and smooth. At last, the magnet density was enhanced to 7.57 g.cm^-3, the coercivity was increased to 1027 kA.m^-1.