The Research Of Hot-deformed Bulk And Radial Ring Magnets

Die-upset is an effective method to produce anisotropic Nd-Fe-B magnets with nanostructure and full density.The grain texture of hot-deformed magnets is along the pressure direction,which helps to prepared radial ring magnets.Although the grain size of hot-deformed magnets reaches nanascale,the coercivity of the magnets is far from the theoretical value,which limits the wide use of the hot-deformed magnets.So it is necessary to research the coercivity mechanism and enhance the magnets coercivity.In this paper,the hot-deformed magnets were prepared by adjusting the temperature,strain rate and mixed the Pr-Cu with Nd-Fe-B powder.The coercivity mechanism of hot-deformed magnets were also researched.And the anisotropic Nd-Fe-B radial ring magnets with no crack and thick wall were prepared by backward extruded process.The following is the main content and conclusion of this paper:(1)The magnetic properties of hot-deformed bulk magnets show the tendency of increasing and then decreasing with the strain rate increased,and exhibiting the best properties when the strain rate is 0.0050s-1.The scanning electron microscopy(SEM)shows that the grains have good alignment when the strain rate is 0.0050s-1,which coincides with the XRD patterns and magnetization results.(2)A small amount of Pr-Cu addition enhances the coercivity obviously.It is observed that the grain size is getting smaller and grain boundary phase is getting thicker after Pr-Cu addition.The angular dependence of coercivity for hot deformation Nd-Fe-B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning.The domain wall pinning is weakened while the nucleation is enhanced after Pr-Cu addition.(3)The ring magnets with no crack and thick wall were prepared by adjusting the backward extruded process.The magnetic properties can be more uniform by designing the mould and some other methods.The maximum energy product((BH)max)and remanence(Br)show a tendency of increasing and then decreasing from the upper end of the ring to the bottom,and exhibit the highest properties in the three-quarter position.And the the magnetic properties increase with strain rates changing from 1.33mm/s to 1.03mm/s for the relative same position.The magnetic properties with 1.03 mm/s in the the three-quarter position are Br=12.83kGs,Hcj=16.39 kOe,(BH)max=36.00MGOe respectively.The SEM shows that the grains have good alignment in a low extruded rate comparing to the higher rate.(4)The remanence of rings from the outer to inner position along the radial direction increased while the coercivity decreased.The SEM shows that the grain have good alignment near the inner surface comparing to the outer surface of the ring magnets.