Surface Modification Of NdFeB Rare Earth Permanent Powders And The Preparation Of Bonded NdFeB Magnets

Bonded NdFeB composite magnets exhibit unique working characteristics that encompass many excellent properties such as highly precise dimension that can be integrally formed with an implemented central axis,cast into various intricate shapes.However,during the preparation of bonded magnets liquidity and oxidation resistance,and adhesive properties of rare earth magnetic powder is the key to improve the magnetic properties.The way of passivation ball milling has been adopted in the process of refining flake NdFeB magnetic powders for the surface passivation membrane,to improve the high temperature oxidation resistance of magnetic powders.The effects of passivation and ball milling process on the magnetic properties and the oxidation resistance of the magnetic properties are studied.At the same time,the influence of the process of preparing the composite bonded magnets with low melting point metal Sn/Zn as binder,and the properties of the composite are studied.The tin/zinc plating layers of the Nd-Fe-B magnetic particles were observed by SEM.The magnetic properties of the coated and uncoated powders were examined by VSM,respectively.Furthermore,both the compressive strength and magnetic properties of bonded magnets were measured.The influence of the magnetic particle content,electric deposition time,current density and passivation agent on the properties of the composite material of the magnetic particle and its composite material were analyzed.For Sn/NdFeB composites,the results indicate that not only the plated-tin and magnetic powders were bonded closely,but also the content of plated-tin can be controlled by the electrical current;The(BH)_max and B_r value of magnetic powders decrease with the increasing content of plated-tin;An increase in the plated-tin content results in an elevation in magnetic properties of composite magnets by warm-pressing preparation.The composite magnets exhibit excellent integrated magnetic property when the content of Sn was 5.079 wt.%,at(BH)max=113.7 k J·m^-3,Br=0.821T,Hcj=732.6 k A·m^-1.The results indicate that the required electrodeposited tin is less than 5 wt.%achieving the same magnetic properties and compressive strength which demands 10 wt.%tin in mechanical mixing method.For Zn/NdFeB composites,the results indicate that electrodeposition of zinc on the surface of the magnetic particles can prevent the oxidation of the magnetic particles at high temperature,thereby improving the magnetic properties of the Zn/NdFeB composite.But zinc is a non magnetic material,the magnetic properties of the magnets can also be reduced.The cathode current density is 2A/dm² and the power deposition time is 30min the magnetic particle can keep its magnetic properties at high temperature.The study found that at elevated ambient temperature with magnetic powder obtained by blank milling will quickly burning compare to other NdFeB magnetic powder coated with different treating agents milling.The use of phosphoric acid,titanate powder treatment agent treatment do its maximum energy product than oxalic acid and a silane coupling agent.Key comparative magnetic energy and oxidation resistance of the phosphoric acid and titanate were treated as a single agent or co-milling process.NdFeB powder with single titanate treatment temperature of100?when the antioxidant properties of the magnetic powder decreased.The description was that titanate film is coated with molecules formed against oxidation at low temperatures more effectively.Phosphate treatment alone,phosphoric acid,and co-processing milling titanate powder can optimize the size and uniformity of dispersion,improved oxidation resistance in magnetic powder after 100?.And after the co-processing of phosphoric acid and titanate powder oxidation resistance better than single phosphate treatment process.Phosphoric oxide film on the surface of powder is more resistant to high temperature oxidation.Phosphoric oxide film titanate molecular film together to make the surface of the protective film magnetic denser.Different milling process resulting powder with increasing temperature magnetic properties has declined.Magnetic powder can decrease the minimum when phosphoric acid and titanate interaction.Especially after 150?,magnetic co-processing of its maximum energy product decline than either phosphoric acid(15%decline)or titanate(down 40%)treated less 10%.When 0.6mol/L phosphoric acid and 0.03mol/L titanate co-processing,optimal oxidation resistance of the magnetic powder.