Research On Magnetic Properties Of Melt-spun NdFeB Powder And Their Bonded Magnets

In recent decades, the market demand of the bonded NdFeB magnets has grown notably because of high magnetic and mechanical performance and good machinability, thus ushering the result that the annual output of NdFeB powder is increasing remarkably. So it's necessary for us to explore the effects and effecting mechanism of alloying component and processing parameters on magnetic properties and microstructure of NdFeB powder. On the basis of modification of the arc-melt spinning wheel, we systematically researched the effects and effecting mechanism of alloying component on magnetic performance and that of technique parameters on magnetic properties. Lots of theoretic analysis had been carried out by use of modern instruments, such as SEM, XRD and DSC. Moreover, some bonded magnets were prepared with Nd10(FeCoZr)83.5B6.5 powder produced by ourselves. We have researched the effects of technique parameters on magnetic properties of these bonded magnets. The main conclusions are achieved as follows:(1) Due to the optimization of alloying component, it proves to be a fact that the magnetic performance of (Nd, Zr)FeB powder is optimal with Nd content 10.5% and B content 6.5%. However the addition of Co doesn't markedly influence the Br and Hcj of Nd10(FeZr)g3.5-xCoxB6.5 alloy. As a result of Zr addition, spinning velocity of 27m/s and optimal annealing condition at 700 ℃ , the energy product of Nd10.5(FeZr)83B6.5 alloy comes up to 14.53MGOe.(2) The experimental results show that partial Zr atom enters the Nd2Fe14B lattice and is behaved as Nd atom. So the addition of Zr can increase practical Nd2Fe14B content, thus ushering the results that Nd10.5Fe81B6.5Zr2.0 alloy mainly consists of Nd2Fe14B single-phase, Br, Hcj and (BH)max are all increasing with the increase of annealing time. On the other hand, the addition of Zr can increase the crystallization temperature of a-Fe and make Nd2Fe14B and α-Fe phases precipitate simultaneously, avoiding the first precipitation and excessive growth of α-Fe. So the magnetic properties remarkably improved with the refined grains and increased exchangecoupling interaction between soft and hard magnetic phases.(3) For the Mo wheel with grooves, the change of melt spinning velocity in a large interval has little effect on magnetic properties, which resolves a technical problem of the performance fluctuation resulting from the fluctuation of melt spinning velocity and the flux of alloy solution.(4) Taking into account the magnetic performance and mechanical properties of the bonded magnets, the optimal mixture ratio of NdFeB powder and adhesive reagent should be 2.5:100, and the optimal powder granularity is 100-120 mesh. With increasing the compressing stress, the Br of the bonded NdFeB magnets is increasing, but the Hcj is declining. So the effect of the value (BH)max on the compressing stress approximates to anti-parabola. The maximal energy product is achieved with the compressing stress at l000MPa.