Laser spot welding of SPCC steel to NdFeB magnets

Mechanical fastening or adhesive bonding is generally used to join NdFeB permanent magnets to steel components, with no research on the welding of magnets to steel. Here, laser spot welding was used to join a NdFeB permanent magnet to SPCC (steel plate cold commercial) steel in a high speed, high quality joining of dissimilar magnet and steel materials. The joint formation mechanism, hardness, strength, and fracture behavior are analyzed. The results show that during the welding process, the two base metals quickly melt, mix and then solidify to form a weld that joins the two specimens together, but that the joint hardness is not uniform with the heat affected zone having lower hardness than the NdFeB base metal. Within the nugget, the region adjacent to the fusion line has the highest hardness while the middle part of the nugget has the lowest hardness in the joint. The maximum fracture stress of the joint is about 75% the strength of the magnet. Hot cracks tend to occur at the interface between the nugget and the magnet base metal, with the cracks propagating and leading to joint failure during shear tests. The fracture is a typical intergrannular brittle fracture.