| Bonded magnets have been widely applied in information, automotive, computer andother fields, because of their advantages such as low cost, large freedom of shape and simpleprocess. Currently, the most widely used bonded magnets are mainly bonded ferrite andbonded NdFeB. Bonded NdFeB magnets have good magnetic properties and poor temperaturestability and corrosion resistance. While bonded ferrite magnets are low cost and goodthermal stability but have relative low magnetic properties. The bonded magnets withmoderate magnetic properties, relative high temperature stability and low cost will beobtained if ferrite and NdFeB is compounded together. New preparation process is adopted toprepare isotropic bonded NdFeB/ferrite composite magnet has become one of the researchfocuses of the magnetic material.In this work, the isotropic bonded NdFeB/Sr-ferrite hybrid magnets were prepared bywarm flow compaction (WFC) technology. The starting materials are isotropic lean-neo,rich-neo, NdFeB/-Fe, HDDR-NdFeB powder and strontium ferrite. The influence of binders,coupling agent, lubricant and WFC process on the microstructure and properties of thebonded hybrid magnets have been investigated in detail. The effects of different mass fractionof Sr-ferrite and different types of NdFeB powders on the magnetic properties and exchangecoupling interaction of the bonded NdFeB/Sr-ferrite hybrid magnets have also been studied.By adding0.5wt%coupling agent, the interfacial bonding force between the binder andmagnetic powder can be improved, the corrosion resistance of NdFeB in the mixed magneticpowder is increased, and the mechanical and magnetic properties of the bonded magnets areenhanced. The content of epoxy resin E-20binder is3wt%of the bonded magnet is best forthe magnetic properties. Zinc stearate lubricant can reduce the friction of the magnetic powderand binder with the mold wall.The process of WFC (temperature, time, and pressure) has a great impact on themicrostructure and magnetic properties of bonded lean-neo/Sr-ferrite hybrid magnets. Themagnetic properties of the hybrid magnets increased firstly and then decreased withincreasing WFC temperature, pressure and holding time. The optimum parameters are90℃ -1100MPa-10min, and the optimal properties obtained by WFC are Br＝0.39T, Hcj＝524kA/m,(BH)max＝21.9kJ/m3.The bonded hybrid magnets with low price and high temperature stability can befabricated by adding appropriate strontium ferrite in lean-neo powder. When the dopingquantity of the strontium ferrite is80wt%, the coercivity temperature coefficient of the hybridmagnets is positive. The bonded hybrid magnets have coercivity enhancement effect withadding strontium ferrite. The bonded strontium ferrite magnets have a strong exchangecoupling interaction at lower magnetic field. However, the md(H) value of the bonded NdFeBmagnets is almost entirely under the curve of the Stoner-Wolhfarth, it shows the staticmagnetic exchange interaction. The md(H) value of the composite magnets prepared by themixing magnetic powders is S-shape due to the dilution effect.The warm flow compaction process has no effect on the coercivity of the bondednano-duplex NdFeB/Sr-ferrite magnet.The bonded nano-duplex NdFeB/Sr-ferrite hybrid magnets have the highest ration ofperformance to price, but lower coercivity. And they are only suitable to fabricate the magnetswith lower coercivity. The over-all magnetic properties of the bonded lean-neo/Sr-ferritehybrid magnets are best, and they are suitable for preparing magnets with higher intrinsiccoercivity and maximum energy product. The bonded rich-neo/Sr-ferrite hybrid magnets havethe same coercivity as the sintered isotropic NdFeB magnets, but the remanence andmaximum energy product is lower, which are suitable for producing the complex shapemagnets with the requirements of high coercive force and low value of high maximum energy.HDDR-NdFeB powder is not suitable for the production of bonded NdFeB/Sr-ferrite magnets.The Henkel plots of bonded lean-neo/Sr-ferrite and bonded HDDR-NdFeB/Sr-ferritehybrid magnets are the typical S shape. The M>0part in Henkel curve of the bondedrich-neo/Sr-ferrite hybrid magnet has two peaks. The exchange coupling interaction ofbonded nano-duplex NdFeB/Sr-ferrite hybrid magnets is almost disappeared and is mainly thestatic magnetic exchange interaction. |
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