Study On The Solidification Structure And Magnetic Properties Of Nd-Fe-B Alloys By Suction Casting

The technology of using copper mold suction casting to prepare nanoscale magnetscontaining small amount of amorphous was used in this paper, at the same time, the effectof the addition of Ti, Zr, and C elements under different thickness on the microstructure ofthe magnets and magnetic energy were studied in this paper. Current people take little onattention on the sheet of Nd-Fe-B bulk alloys.But flaky chunk of alloy was easy to befacilitated than the rod-like alloy, so this experiment will focus on the sheet of Nd-Fe-Bchunk of alloy.Sample preparation process was as follows: firstly, meltedthe sample by electric arcunder the protection of argon atmosphere. Master alloy ingot should melted six times inorder to ensure the uniformity of melt and the stable use of performance; secondly, put thealloy ingot into a hemispherical slot and melted again; the last, Melted master alloy wasput into the suction casting room vacuumed, the master alloy melt wad inhaled into thewater-cooled copper mold by the role of different pressure. So the preparation of samplewas completed.The results showed that: the sample of Nd7Fe75Ti2B16of which the sickness was3mm had taken on the characteristics of directional solidification because of one-way heattransfer conditions on both sides of the mold, and then had formed forming a flake crystalstructure. The columnar grains had disconnected into several small piecees on the surfaceof sample and the center of transitional region, we can determined from the orientation thatthis should be part of the fuse to form the flaky crystal overheating caused. Nd7Fe75Ti2B16alloys of which the sickness was0.7mm had showed more strong c-axis preferredorientation than that of3mm. This was because the formation of texture along the fillingdirection was closely related to tensile deformation and cooling rate.To further investigate the impact of adding elements on the microstructure of suctioncasting samples, we also prepared Nd₆Fe_62-2xCo₁₀Zr_xC_xB₂₂（x=0,0.4,0.8,1.2,1.6） alloyof which the sickness were0.7mm and3mm. The study found that: with the increase of thecontent of （Zr, C）, the diffraction peaks of the samples of α-（FeCo） of which sickness was3mm gradually decreased indicating that the addition of composite elements （Zr, C） hadinhibited the precipitation of α-（FeCo） phase. However, when the content of （Zr, C）element was excessive, α-（FeCo） again increased, that was to say, Excess （Zr, C）had little effect on the inhibitory of the precipitation of α-（FeCo）. When the thickness was0.7mmand the x was0, the precipitation of α-（FeCo） inhibited was up to8.7wt%. In addition,amorphous phase was found in the sample when the thickness was0.7mm.In order to investigate the impact of thickness on the microstructure, we had alsoprepared Nd₆Fe_62-2xCo₁₀Zr_xC_xB₂₂（x=0,0.4,0.8） alloy, and the thickness were1.2mm,1.4mm,1.5mm. The study found that: the thickness of sample would have a major impacton the microstructure morphology and grain size of solidification, when the range of x was0,0.4,0.8and the thickness were1.2mm,1.4mm,1.5mm, the grain size of the sample was30.3nm、28.2nm、26.6nm, which was in contrast with that of sample of1.2-1.5mmthickness.Finally, we had taken on a test on magnetic property of Nd₆Fe_62-2xCo₁₀Zr_xC_xB₂₂（x=0,0.4,0.8,1.2,1.6） of which the thickness was0.7mm and Nd₆Fe_62-2xCo₁₀Zr_xC_xB₂₂（x=0,0.4,0.8） of which the thickness was1.2-1.5mm. The results showed that: Nd6Fe62-2xCo10ZrxCxB22（x=0,0.4,0.8,1.2,1.6） was prepared by copper mold suction casting, ithad exhibited better soft magnetic properties when the thickness of sheet was0.7mm thanthat of1.2-1.5mm. When the thickness was0.7mm and the x=0, the saturationmagnetization was1.27T. The sheet alloy with1.2-1.5mm thickness has lower softmagnetic properties than that of0.7mm.This should be related with the increase of crystalphase.