The Study Of High Performance Sintered Nd Fe B Magnets

The Nd FeB magnet is divided into two kinds according to its Manufacturing technology,one is sintered Nd-Fe-B and the other is bonded Nd-Fe-B.As the third-generation permanent magnet,NdFeB magnet has the highest magnetic performance,rapid development and wide application.It is mainly used in the various fields,for example,wind power generation,transportation,aerospace,computer,household appliances,medical treatment,etc.Wind power generation is a kind of cheap and abundant new clean energy,the market prospect is broad.However,the poor operating environment with high temperature,severe cold,wind erosion and dampness cause a short working life,the higher requirements for the comprehensive performance of magnets is needed.The theoretical magnetic energy product of the NdFe B magnet reaches 64 MGOe,and laboratory samples reached 59.6 MGOe in 2006[1].The sintered Nd-Fe-B magnets used in wind power generation are 38H,45H and 52H magnets,of which 38H and 45H magnets have been mass production.Few companies can produce high performance 52H magnets,because of obsolete production equipment and poor technology.In order to further develop the market of sintered Nd-Fe-B magnet applied to the high fields,we studied the new technology of making high performance magnet.The thesis focuses on using advanced production equipment,double alloy technology and optimizing alloy composition to satisfy requirements of high performance52H magnet.Taking the 52H product as an example,the sintered Nd-Fe-B magnets were prepared by using the strip casting technology,hydrogen decrepitation,jet milling process,pressing process and vacuum sintering technology.The main parts of smelting furnace,especially the width and height of the tundish outlet and the speed of the copper roller were improved and adjusted.The consistency of alloy thickness has been improved and the majority of alloy thickness is controlled between 0.2 and 0.4 mm.The melting technology of alloy was optimized,including the melting temperature and pouring temperature which were suitable to 52H magnet.The microstructure of the main phase and the grain boundary phase were improved by using dual-alloys technology and the multiple elements adding methods and microstructure control technology.The metal elements Dy,Ga,Cu,Al were added during the melting process,the influences of different cooling rates on the microstructure of the alloy were investigated.The prepared alloy appeared the uniform columnar crystalline structure without crystal defects,such as isometric crystal,amorphous phase andα-Fe phase.The Nd-rich phase of the prepared alloy was distributed uniformly without Nd-rich phase agglomeration phenomenon.Therefore,the prepared alloy provides the basis of manufacturing high-performance 52H magnets.The microstructure of the magnets was optimized by adjusting sintering temperature,heating rates and vacuum degree during the sintering process.At the same time,oxygen levels were controlled strictly to prevent the decrease of magnetic properties during the production process.Finally,the performance of the produced columnar magnet sample at 20℃（D10*10 mm）satisfies:B_r≧14.2 kGs,H_cj≧17.5 kOe,and H_K/H_cj≧0.97.