Research On The Preparation And Performance Of Bonded Nd-Fe-B Composite Magnets

As an essential electronic component,the bonded magnets with the advantages of fast forming,low cost,and a high degree of shape freedom have attracted wide attention influenced by the rapid development of new energy vehicles,wind power generation,and electronic technology products in recent years.However,the existing bonded magnets have the disadvantages such as poor temperature resistance,poor corrosion resistance,and low mechanical properties,which limit their wide application in high-end fields.We first prepared the binders with high-temperature resistance,high mechanical properties,and strong corrosion resistance.We then fabricated various high-performance bonded Nd-Fe-B magnets by molding method and revealed the bonding mechanism with different binders and the performance enhancement mechanism of the corresponding bonded magnets.This paper explored the innovative application of 3D printing technology to prepare bonded Nd-Fe-B magnets based on the traditional preparing process.The 3D printed high-performance isotropic and anisotropic magnets were realized using different polymer-based binders to adjust melt viscosity suitable for 3D printing.In this paper,two kinds of high-performance epoxy resin(EP)/sodium silicate(SS)composite binders were prepared by physical blending and chemical modification methods.The performance enhancement mechanism of composite binders on the properties of bonded Nd-Fe-B magnets was studied.The results show that the magnet prepared by EP/SS physical blending binder has better moisture resistance than that of SS bonded magnet due to EP's excellent hydrophobicity in the EP/SS binder.The SS can effectively enhance the heat resistance and corrosion resistance of the EP binder.Therefore,EP/SS binder can endow better overall performance for the bonded magnet.However,EP/SS bonded Nd-Fe-B magnets still exhibit corrosion behavior after exposure to a moist environment for a long time due to the poor compatibility between EP and SS.Therefore,W-EP/SS binder with excellent compatibility was prepared by chemical modification of EP monomer.The results show that coercivity,remanence,and magnetic energy products of the W-EP/SS bonded magnets are 9.73 k Oe,6.28 k G,and 8.42 MGOe,respectively.W-EP/SS bonded magnet's magnetic performances are higher than those of EP,SS,and EP/SS bonded magnets.Simultaneously,the W-EP/SS chemical composite binder can also obtain stable temperature resistance and corrosion resistance,which plays an essential role in resisting 200?high temperature and humidity working conditions.Besides,the compressive strength of the W-EP/SS bonded magnet at 20?and 200?reaches 95 MPa and 40.6 MPa,respectively,which are significantly higher than that of EP/SS bonded magnet.The microstructure analysis shows that W-EP/SS binder can form a dense anticorrosive film on the magnet's surface,which can prevent the corrosion behavior of the magnet.Meanwhile,Si-O-Si and C-O-C's higher chemical bond energy in the W-EP/SS binder can effectively improve the magnets'compressive strength and high-temperature resistance.In this paper,two kinds of liquid binders,Phenolic Resin(PF)and 4,4diaminodiphenylmethane epoxy(DDM-EP),were used to prepare bonded Nd-Fe-B magnets with excellent high-temperature resistance and high mechanical properties.The results show that a liquid binder with a rigid chemical structure and good fluidity is an essential factor in improving magnets'temperature resistance and mechanical properties.For PF/Nd-Fe-B bonded magnets,although the coercivity is slightly lower than that of conventional EP bonded magnets at room temperature,PF bonded magnets can maintain good dimensional stability,obtain functional magnetic properties at 200?.At the same time,this bonded magnet can get higher mechanical properties.The compressive strength of bonded magnet with 4 wt.%PF content can reach 253.6 MPa,which is more than 10 times of EP bonded magnets.Besides,the thermal resistance and mechanical properties of the DDM-EP bonded magnet were significantly improved by introducing DDM with a rigid structure.The results show that the EP binder with 20 wt.%DDM can be fully cured to enhance the temperature resistance and high temperature dimensional stability of the DDM-EP bonded magnet.Simultaneously,the compactness and uniformity achieved the best,and the maximum compressive strength can reach 138.4 MPa,which is much higher than that of the commercial EP bonded magnet.The liquid binder bonding mechanism was revealed by analyzing PF/Nd-Fe-B and DDM-EP/Nd-Fe-B bonded magnets'internal structure and fracture morphology.During pre-pressing and isostatic pressing densification,the magnetic powders can be stacked in sheets perpendicular to the pressure direction due to the liquid binder's hydrophobic and permeable action,which can increase the structural regularity of the magnet.Simultaneously,the binder with rigid structural groups forms a solid cross-linking network structure during the curing process,which improves the temperature resistance and compressive strength of the magnet.Besides,liquid adhesives can also significantly reduce the forming pressure of the bonded magnet,which is conducive to saving the mold's cost and having a reasonable prospect of industrial application.Based on the traditional molding process,a systematic study has been carried out around the 3D printing technology for new boned permanent magnet materials,involving the anti-oxidation modification of magnetic particles,preparation of isotropic and anisotropic 3D-printed Nd-Fe-B magnets.Under the conditions of400?-3 h,a layer of Zn shell structure with a thickness of 1-2?m was formed on the surface of MQP-S Nd-Fe-B magnetic powders by a rotational diffusion process,which effectively reduced the oxidation degree of magnetic particles based on maintaining the original excellent magnetic properties.Subsequently,the Zn-MQP-S particles and polylactic acid(PLA)resin binder were used to prepare the 3D-printed isotropic magnet with magnetic particle content of 86 wt.%.The magnet's density and the maximum magnetic energy reached 4.08 g/cm~3 and 2.8 MGOe,respectively.To further improve the magnetic properties of 3D-printed magnets,small-sized Sm Fe N and large-size HDDR composite magnetic powders were used to prepare 3D-printed anisotropic magnets with excellent performance.When the content of composite Sm Fe N/HDDR magnetic particles with the ratio of 6:4 was 90 wt.%,the coercivity,remanence,and maximum magnetic energy product of the anisotropic 3D-printed magnet reached 13.50 kOe,4.37 kG,and 4.37 MGOe,respectively.