| Injection Molding (IM) has great advantage to manufacture magnets with thin wall, complex shape, high tolerances, radial alignment, and assembly forming. Meanwhile, it has high materials utilization and productivity. IM bonded magnet meets the trends of electronic devices to small volume, light weight, integration assembly, high efficiency and energy-saving. Therefore, it attracts extensive attention and is undergoing rapid development and industrialization. However, its development in China is lagged behind, and there is a long way to reach the international level. In order to make full use of the sufficient domestic supply of rare-earth resource and develop Nd-Fe-B permanent magnets industry, this dissertation is focused on the research of manufacturing IM Nd-Fe-B bonded magnet with high performance, and some analytic techniques including DSC, SEM, IR and XRD are performed to investigate the surface modification of powder, the preparation of new binder, influence of process factors such as mixing, injection, magnetic field alignment.The coating method combined organic solvent phosphatisation and complex silane coupling agent were utilized to modify HDDR Nd-Fe-B magnetic powder. Because of the forming of double protecting film composed of passive phosphate and silane coating, the oxidation resistance of magnetic powder is improved remarkably. The oxidation activation energy and oxidation temperature of Nd-Fe-B powder is increased from 45.7kJ/mol to 88.9 kJ/mol and 179.7℃ to 326℃ respectively, and the surface properties of magnetic powder and interfacial adhesion between powder and binder are improved, which is believed to be due to chemical bonding and physical adsorption of the present polar groups in the silane. Therefore, dispersibility and compatibility of magnetic powder with binders are improved. As a result, the flowability of feedstock, magnetic properties, compressive strength, corrosion resistance of bonded magnet are enhanced, and the effect is best when powder adhere with silane in monolayer.Particle size of Nd-Fe-B powder has a great effect on the alignmentdegree, remanence, intrinsic coercivity and maximum energy product of IM bonded magnet as well as its density and heat resistance. The optimal particle size of the magnetic powder with better properties is in the range of 80 μ m~100 μ m. Appropriate particle size distribution can reduce the apparent viscosity of the feedstock and increase its tap density, powder volume fraction and flowability. The best particle sizes distribution was obtained, which is composed of 8mass% 106~150 μ m powder, 58mass% 75-106 μ m powder, 25mass% 45-75 μ m powder, and 9mass% <45 μ m powder.An advanced injection machine was developed, which has a powerful magnetic alignment device. Hollow copper wire was adapted instead of flat wire to form multi-units coil. Therefore, the increase of temperature of the electromagnetic coil is avoided, and magnetic field becomes stable and its intensity is also improved. Moreover, combining the two magnetic yokes in the coils with central yoke in die, transition between axial alignment and radial alignment can be realized easily, so that the appliance range is broadened.Through investigating the influence of mixing, injection and alignment magnetic field process on the properties of Nd-Fe-B bonded magnet, the optimal process parameters are obtained as follow: injection temperature 280°C, die temperature 90°C, injection pressure 70~120MPa, injection velocity 60%~80%, alignment current 75A and alignment time 4s.Based on the compatible theory and acting mechanism of addition agents, p-toluene sulfonamide, compound of 50mass% octadecanamide and 50mass% methyl polysiloxane fluid, compound of 30mass% 1010 and 30mass% DLTP and 40mass% MD1024, and MoS2was adapted as plasticizer, lubricant, antioxidant, nucleator for polyamide resin respectively. When their dosages in PA12 resin are 8mass%, 10mass%, 4mass%, 0.4mass% respectively, the binder is of lower viscosity, better flowability, and high mechanical properties. The binder is more sensitive to temperature than shear rate, and its fluid exponent and activation energy are 0.64 and 69 kJ/mol respectively at 280°C and shear rate 1619s"1. The injection molding Nd-Fe-B bonded magnet with highperformance which reach international advanced level was obtained with the powder volume fraction of 65vol%. Its remanence Br, intrinsic coercivity Hq, the maximum energy product (BH),^ and compressive strength o bb are 878mT, 1212.3kA/m, 128kJ/m3, 73MPa respectively.Influence of aging temperature(T), height diameter ratio(H/D), intrinsic coercivity(Hcj) and powder volume fraction (?) on irreversible magnetic flux loss of the bonded magnet (hjn) was investigated. In order to present their relationship, a mathematical model is established by regression method, which is shown in the equation as hirr=-12.54-0.035H/D-0.0088D-0.017Hcj+0.4T+0.072O.The bonded magnet composed of the coarse Nd-Fe-B powder with high magnetic properties and the fine ferrite or Nd-Fe-N powder with low magnetic properties exhibits good properties and produce complex effects caused by the magnetic dipole field of anisotropic powder. In the course of Nd-Fe-B/Fe3O4 magnet with Fe3C>4 of less 70mass%, the magnetic properties are more than the average and reach the maximum when two kind of powder have equal volume fraction. However, when Fe3C>4 fraction more than 70%, its magnetic properties is less than average. For Nd-Fe-B/Nd-Fe-N bonded magnet, the complex effect don't depends on the volume fraction of Nd-Fe-N powder. Its intrinsic coercivity is always less than the average, meanwhile its remanence is more than average.In order to decrease the oxidation of Nd-Fe-B magnetic powder, a new type of thermoplastic-thermosetting binder was developed ,which can be injected at temperature 115°C. This binder is composed of 74mass%EP, 6mass%DICY and 20mass%PA12-6. The binder exhibit thermoplastic behavior during injection, and its compact can be easily to be removed from the die and can produce automatically. In addition, it exhibits high strength due to curing of thermosetting resin. The activation energy and fluid exponent of feedstock at powder volume fraction of 60vol% are 34.3kJ/mol for 1619s'1 and 0.44 at 135°C. The optimal cured process of its bonded magnet are as follows: cured temperature 190°C, nitrogen atmosphere, and curing time 120 min. The best properties of magnet are (BH)max84.5kJ/m3, Br 730mT> Hcj949kA/m> o bb105MPa.When compared with PA12-based magnet with same volume fraction, its magnetic properties are almost the same, but the mechanical properties are better. Even at 180°C, its compressive strength can maintain 65MPa, so it can be applied in the manufacture of high temperature bonded magnet.By adding PA66 into PPS to form 80PPS/20PA66 blends, there was no unfavorable effect, moreover its flowability and impact strength are improved remarkably. By replacing PPS by 80PPS/20PA66 blends as the binder, high temperature Nd-Fe-B bonded magnet produced by injection molding exhibits better magnetic properties and higher powder volume fraction.
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