Study On Processes Of High-Performance Sintered Nd-Fe-B Magnet Prepared By Dual-Alloy Method

Since sintered Nd-Fe-B alloys have been found in 1983, as the third generation of rare-earth permanent-magnet material, because of its high performance (the theoretical magnetic energy product is 64MOe)and the high cost performance ratio it has been developed rapidly. we are rare-earth rich country, which occupates 80 percents of the world storage capacity, and which is our biggest dominance in the development of rare-earth permanent-magnet material. However, the manufacturing technique in most of our industry fall behind of Japan and America, and the products quality is not so good, which leads to the disadvantage in the market competition. As a result, increasing the performance of sintered Nd-Fe-B magnets is a problem that many industry must face. On the base of the existing equipments, how to improve the performance of sintered Nd-Fe-B magnets is the departure point of this article.In order to obtain the best magnetic performance sintered magnets ,At beginning of this article the structure of Nd-Fe-B alloy cast ingots were analysied. Binary alloy technology ,controlling the technology parameter effectively and HD process were also empolyed.The analyse on the structure of Nd-Fe-B alloy cast ingots indicates that the cast ingots produced by existing melting equipments will precipitate muchα-Fe when the percentage composition of rare-earth depresses.The existence ofα-Fe in cast ingots,not only decreases the numerical measure of Nd2Fe14B phase in cast ingots,but also has bad influence on the latter powder-making and shaping process,especially disserves the performance of sintered Nd-Fe-B magnets severitily which expressed specificly in the departments that the remnant magnetism and magnetic energy product don't increase as the result of the decrease of the rare-earth content,and the intrinsic coercive force is also influenced.Therefore,adopting the manner of vacuum high temperature annealing can cancelα-Fe in cast ingots.By using the cast ingots after annealing to make sintered magnets directly ,the remnant magnetism and magnetic energy product increase significantly,but intrinsic coercive force is relatively low.Therefore, two composition metal technology is adapted to increase the coercive force of the magnets.the main alloy comopsition is close to Nd2Fe14B phase,the assistant phase is Nd-rich phase.The main phase eliminatesα-Fe by high temperature annealling. After HD process the main and assistant alloys are staved ,and then they are mixed according to determinate ratio ,made to powder by jet mill, magnetic orientationshaping ,sintered,backfired,and made to sintered magnets.Through the analysis of the powder after HD process and magnet structure,adapting HD staving can improve the character of the powder and increase the magnetic performance.After the invetigation of the sinter and backfire processes on binary alloy technology,the sintered temperature of binary alloy technology is higher than tradition magnets. Its best sintered temperature is 1105℃,and its best backfired temperature is 520℃.By analysing the influence of the mixed proportion of the main and assistant alloys on the magnet performance,when the proportion is 93:7 and the theoretic composition two phase alloys are Nd30.23Pr1.05Dy0.7B1.07Nb0.279Al0.186Cu0.07Fe66.415 ( wt% ) , two phase alloys achieves the best magnetic performance that the magnetic energy product is 45MGOe and the intrinsic coercive force is 13.8kOe.