| Sintered NdFeB magnet has been widely used in electronics, computer,automobile, machinery and medical equipment for its excellent magnetic properties.However, the poor corrosion resistance greatly hinders its further wide applications.In order to improve the corrosion resistance of NdFeB magnet, magnetron sputteringand electron beam evaporation method were employed to prepare the protectivecoatings on NdFeB. And the corrosion behavior of NdFeB and its protective coatingsunder magnet field action was investigated.Pure Al coating was deposited on sintered NdFeB magnets by direct currentmagnetron sputtering. The influences of sputtering pressure, sputtering power andcoating thickness on microstructure and properties of Al coating were investigatedsystematically. As increase the sputtering pressure, the deposition rate decreases andAl coating changes to be loose and porous, thus the corrosion resistance reduces;with the increasing of sputtering power, the deposition rate increases, but Al coatingchanges to be scattered and loose, therefore the corrosion resistance decreases; asincrease the coating thickness, the compactness of Al coating has a increased trendup to6.69μm and then transforms to decreases, and the6.69μm Al coating has thebest corrosion resistance.The optimal sputtering pressure, sputtering power andcoating thickness is0.5Pa,51W,6.69μm, respectively.Protective aluminium oxide coating was deposited on sintered NdFeB magnetsby electron beam evaporation. And Al coating was also prepared as a comparison.The effects of coating thickness and deposition rate on microstructure and propertiesof Al2O3coating were researched. The Al2O3coating can provide protection forNdFeB. And the effect of coating thickness on corrosion resistance is not distinct,but the corrosion resistance can be significantly improved by appropriatelyincreasing deposition rate.To further understand the corrosion properties of sintered NdFeB magnet inpractical application, the corrosion behavior of magnet and its protective coatingsunder magnet field action was studied. The electrochemical reaction mechanism ofNdFeB and its protective coatings in different corrosion medium is not effected bymagnetic field; magnetic fields accelerate the corrosion rates of NdFeB and theprotective coatings in NaCl solution, and the opposite results arefound in passivationH3PO4and NaOH solution; with the increase of magnetic field intensity, the magnetic effect coefficient has maximum value. |
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