Research Of Problems In Preparing The Sintered NdFeB Permanent Magnets

This paper presents comparatively systematic research of Problems met in preparing the Sintered NdFeB Magnets, including the optimization of the micro structure of sintered NdFeB magnets, impact of the powder-fabricating and sintering techniques to the magnetic properties; so as to explore the feasibility of adjusting the strip casting techniques to achieve sintered NdFeB magnets with high performances.The result shows good cast bar structure is one of the key issues to achieve sintered NdFeB magnets with high performances. The good cast bar structure is determined by the preparing techniques of the cast bars. Strip casting structure is completely satisfying the request of making excellent cast bar structure.Hydrogen decrepitation powder-fabricating technique must be used to substitute classical shell-like alloy cast bar with strip casting. Most ball-grinding powders, which are get from hydrogen decrepitation powder-fabricating technique are polycrystalline, which we assume will affect tropism so as to get low magnetic properties. Further research of powder-fabricating technique to make sure most powders are single crystals and uniform is needed to improve magnetic properties.Excess growth of majority crystal should be avoided while accomplishing compactsintered magnets. Best sintering temperature for impacted blank is affected by the powder size. The lower the proper sintering temperature, the finer the powder size. Sintering heat preservation time is relative to sintering temperature. Remanence and (BH)m increase with the increase of temperature when the sinter temperature is lower than the proper ones. Remanence and (BH)m decrease with the increase of temperature when the sinter temperature is higher than the proper ones. Coercive force decreases with the increase of the sintering temperature. Tempering treatment will drastically increase the sintering coercive force of the sintered NdFeB magnets.