| In recent years,bonded NdFeB magnets have become the most attractive rare earth permanent magnet material due to their advantages of lightness,thinness,precision,high efficiency,and energy saving,which widely used in various types of micro motors and sensors such as automobiles,storage media,smart home appliances,etc.Especially,with the development of new energy vehicles,more requirements are put forward for the development of high magnetic and high corrosion resistance NdFeB magnets.In this paper,a high-precision bonded NdFeB magnetic ring is prepared by the compression molding method,and ZnAl coating and ZnAl/epoxy resin coating are prepared on the surface by high-pressure spraying process.This provides a useful exploration for the industrial development of bonded NdFeB magnets with high corrosion resistance.A kind of high-precision bonded NdFeB magnetic ring was prepared by the processes of component design,magnetic powder pretreatment,mixing and granulation,molding and solidification.The surface accuracy and surface morphology of the bonded NdFeB magnetic ring were characterized,and the magnetic properties and mechanical properties were tested.The results show that the optimal content of the binder is 3 wt%,which is consistent with the theoretical model calculation.The particle size of the magnetic powder is adjusted by mixing magnetic powder,and its magnetic performance is the best.The size of the magnetic ring made by the best technology:outer diameter is 22.2±0.05mm,inner diameter is 19.7±0.06mm,height is 12.3±0.03mm,parallelism is 0.03mm,roundness?0.03mm,concentricity?0.03 mm,full-size CPK?1.33 the magnetic properties of the magnetic ring are:remanence Bris 6.72 k Gs,intrinsic coercivity Hcj is11.38 k Oe,and maximum magnetic energy product(BH)max is 9.49MGOe(75.57KJ/m3),The magnetic flux is 4.72 m Wb the density of the magnetic ring is about 5.9g/cm3,and the compressive strength is 65N.By means of high-pressure air spraying,the bonded NdFeB magnetic ring showed that a ZnAl coating was prepared.The surface and cross-sectional morphology and element composition of the ZnAl coating were characterized.ZnAl was studied through electrochemical experiments and neutral salt spray experiments.The corrosion resistance and corrosion resistance mechanism of the coating were tested,and the magnetic flux changes of the magnetic ring before and after the ZnAl coating were tested.The results show that the ZnAl coating is aluminum white,and the thickness of the coating is about16.7?m.Zn flakes and Al flakes exist in the coating in the form of simple metal,and they are uniformly and densely coated on the NdFeB bond magnet in the form of fish scales.On the surface of the ring,the cross-section of the coating is a sheet-like stacked structure.After the ZnAl coating is applied,the self-corrosion current density of the bonded NdFeB magnetic ring exposed to 3.5wt%Na Cl solution is reduced by at least one order of magnitude,the neutral salt spray test time is extended by about 264 hours,and the corrosion resistance is greatly improved improve.After the ZnAl coating is applied,the magnetic flux of the NdFeB magnet is only reduced by 0.15%to 0.55%,indicating that the ZnAl coating and its preparation process will not damage the magnetic properties of the NdFeB bonded magnetic ring.The ZnAl/epoxy composite coating system was prepared on the surface of NdFeB bonded magnetic ring to achieve the purpose of long-term effective corrosion protection of NdFeB bonded magnetic ring.The surface and section morphology and profile of the composite coating were characterized,the corrosion resistance was tested,and the corrosion mechanism was studied.The results showed that:The epoxy resin coating penetrates into the holes of ZnAl coating and plays a good sealing role.There is no obvious dividing line between coating and coating or between coating and substrate,which proves that it has a strong binding force.The decrease of the surface roughness of the composite coating is beneficial to decrease the activity of the coating.After coating with ZnAl/epoxy resin composite coating system,the self-corrosion current density of bonded NdFeB magnetic ring in 3.5wt%Na Cl solution decreased by about 4 magnitude,and the neutral salt spray test reached 1800 h.The ZnAl/epoxy composite coating can play a double superposition effect of preventing the movement of corrosive medium and electrochemical protection.Among them,the co-penetration of epoxy resin particles,the passivation of Zn-Al and the sealing and blocking of corrosion products are synergistic factors,which make the corrosion resistance of the coating far better than that of the traditional single coating.The ZnAl/epoxy composite coating was prepared on the surface of the NdFeB bonded magnetic ring to achieve the purpose of long-term effective corrosion protection for the NdFeB bonded magnetic ring.The surface and cross-sectional morphology of the composite coating were characterized and tested.Corrosion resistance,and its corrosion mechanism has been studied.The results show that the epoxy resin coating penetrates into the ZnAl coating hole and plays a good sealing role.There is no obvious dividing line between the coating and the coating or between the coating and the substrate,which proves that it has a strong bonding force.The surface roughness of the ZnAl/epoxy resin coating is reduced,which is beneficial to reduce the activity of the coating.After coating the ZnAl/epoxy composite coating system,the self-corrosion current density of the bonded NdFeB magnetic ring in 3.5wt%Na Cl solution decreased by about 4 orders of magnitude.The neutral salt spray test reached 1800 h,and the ZnAl/The epoxy resin composite coating can exert the dual superimposing effect of hindering the movement of the corrosive medium and electrochemical protection,including the co-permeation of epoxy resin particles,the passivation of Zn-Al,and the sealing and blocking of corrosion products.So that its corrosion resistance is far better than the corrosion resistance of the traditional single coating. |
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