A Study Of Key Techniques For Mass-production Of High-performance Sintered Nd-Fe-B Magnets

Effects of Gd, Ho or Dy2O3 additions on the microstructure and magnetic properties of sintered Nd-Fe-B magnets were investigated. Based on the analysis of the microstructure features of book-like and scale-like Nd-Fe-B alloy ingots, 42SH,38UH, and 35EH high-performance sintered Nd-Fe-B magnets have been successfully mass-produced by optimizing the compositions and key process parameters.There was a certain influence on the microstructure and properties of sintered Nd-Fe-B magnets when a certain amount of Gd or Ho was added. After adding the right amount of Gd or Ho, the formation ofα-Fe phase was inhibited in Nd-Fe-B alloy ingots, the growth of Nd2Fe14B column crystals was promoted, the Nd-rich phase was uniformly distributed. The magnetic grains were refined to some extent, the microstructure of sintered Nd-Fe-B magnets was fine and uniform, the defects, such as holes, were reduced so that sintered Nd-Fe-B magnets became more compact. Adding Gd or Ho could dramatically increase the intrinsic coercivity, slightly decrease the remanence and energy product, significantly improve the thermal stability and corrosion resistance. Addding Gd or small amount of Ho could greatly improve the squareness of J-H demagnetization curve, but adding excessive Ho could greatly decreaseed the squareness of J-H demagnetization curve.There was a certain influence on the microstructure, orientation degree, and magnetic properties of sintered Nd-Fe-B magnets when a certain amount of Dy2O3 was added. After adding the right amount of Dy2O3, Dy could enter the matrix phase, which enhanced the anisotropy field of the matrix phase, so the intrinsic coercivity was significantly improved, and the squareness of J-H demagnetization curve was greatly improved, but the remanence and energy product were slightly decreased. With the incresing Dy2O3 amount, the density of sintered Nd-Fe-B magnet was decreased, and the orientation degree of magnet was significantly improved with more than 1.2%Dy2O3 additions.With some experimental results obtained earlier, the raw materials and the equipment generally used in domestic industrial production of sintered Nd-Fe-B magnets, We produced three kinds of sintered Nd-Fe-B magnets-42SH, 38UH and 35EH by optimizing the compositions, improving the techniques of alloy ingots, preparation of alloy powders, magnetic field orientation and molding, and sintering. After being applied, they met the application requirements of user. At the same time, three high-performance sintered Nd-Fe-B magnets did not contain Tb so that they saved production cost and improved the market competitions.