Improved Microstructure and Mechanical Properties for Sintered NdFeB Permanent Magnet/steel Soldered Joints by Nd Addition

Sintered NdFeB permanent magnets with excellent magnetic properties are widely used in electromagnetic devices. The effect of Nd addition on microstructure and mechanical properties of sintered NdFeB permanent magnet/steel soldered joints was investigated by computational thermodynamics approach and coefficient of thermal expansion. The formation of NdSn3 after doping minor Nd into Zn-Sn-Bi solder improved the mechanical properties of soldered joints. On the one hand, NdSn3, as a low Gibbs free energy phase, promoted the heterogeneous nucleation of the ? -Sn, resulting in the grain refinement. On the other hand, NdSn3 with lower coefficient of thermal expansion was beneficial for relaxing the residual stress.