Microstructure and Properties of Soldering Sintered NdFeB Permanent Magnet to DP1180 Steel Using Zn-based Alloy

Sintered NdFeB permanent magnet (NdFeB) was firstly soldered with DP1180 steel using Zn-5Sn-2Cu-1.5Bi (ZSCB) solder. Soldering was performed in an inert atmosphere control high-frequency induction furnace, and then the microstructure, magnetic properties and shear strength were investigated by optical microscope, scanning electronic microscopy, energy dispersive X-ray analysis, NIM-2000H magnetic tester and mechanical testing machine. Results show that the interface between NdFeB/ZSCB solder forms metallurgical bonding with Nd-Fe-Zn and Fe-Zn. FeZn13, FeZn10 and Fe3Zn10 phases form in steel side of the joints. Besides, the soldering temperature has slight influence on the magnetic properties of NdFeB. Finally, compared with adhesive bonding in traditional method, the shear strength of the soldering joints is dramatically improved by 35.38%, from 32.50 MPa to 44.00 MPa. The shear strength is high enough to cause failure in NdFeB side of the joints. Fracture of the joints is caused by large difference of thermal expansion coefficient between NdFeB and ZSCB solder as a result of high stress at the reaction layer close to NdFeB.