The Study Of Rare Earh On Properties And Coercivity Mechanism Of Hot-deformed Nd-Fe-B Magnets

Neodymium iron boron permanent magnetic material can be used in a variety ofindustries since it has been found, especially in wind power generation, energy-efficientappliances, electric cars and clean energy for its excellent integrated magnetic properties. Itsproduction and consumption are increasing year by year. In recent decades, the marketdemand of hot-deformed NdFeB magnets has grown notably because of great environmentalstability and lower preparation cost, thus ushering the result that the market demand ofmelt-spun NdFeB powders and hot-deformed magnets is increasing remarkably. Restricted bythe equipment conditions and patent qualification, inland powders have no consequence inmarket because of low integrated magnetic properties. So it’s necessary for us to explore theeffects and effecting machanism of component on magnetic properties and microstructure ofNdFeB powders and magnets.In this paper, the melt-spun NdFeB ribbons with different rare earth content were madeand mechanically crushed, and then the anisotropic hot-deformed magnets were produced bydie upsetting the hot-pressed precursors. The influence of rare earth content on magneticproperties and microstructure of the melt-spun powders and hot-deformed NdFeB magnetshave been investigated. Coercive force of the melt-spun powders and hot-deformed magnetsalmost showed a monotonic increase with the increasing of RE content. The analysis ofmicrostructure of the melt-spun ribbons indicates that the average grain size is decreased withthe increasing of RE content. The influence of rare earth content on bending strength ofhot-deformed NdFeB magnets have been investigated. The result shows that bending strengthparallel to c-axis orientation increases with the increasing of RE content, while thatperpendicular to c-axis orientation exhibits decrease. The shape anisotropy of the grains and the distribution of RE-rich phase in hot-deformed Nd-Fe-B magnets should be related to themechanical anisotropy, and the anisotropy of bending strength is more obvious with theincreasing of RE content.The magnetization behaviors of different RE content are investigated. The shape of themagnetic domain of the remanence state is much different from that of the thermallydemagnetized state. This result is caused by the irreversible domain wall motion when theexternal magnetic field gets close to the coercivity of the sample. The samples show the largedegree of reversible and open recoil loops, which indicate that the hot-deformed magnets areinhomogeneous maybe resulted from the difference of microstruction or compositiondistribution. The inhomogeneity will result in the magnetic "harden" inhomogeneity. Inhot-deformed magnets the inhomogeneity maybe resulted from the difference of grains size orthe irreversible magnetization process. The opening size of the recoil loops in thedemagnetization process decreases while the content of rare earth increases from12.8to14.33at%, which indicates that the increase of rare earth content could optimize themicrostructure. Meanwhile, the intergrain exchange coupling becomes weaker and thedistribution of the irreversible nucleation field becomes narrower and the squareness of themajor demagnetization curve is finer with the increasing of the RE content. The mechanism ofthe coercivity is of a typical pinning type of the inhomogeneity domain wall and the effect ofpinning is more obvious with the increasing of RE content.