Effects Of Nanopowders Addition On Corrosion Resistance Of Sintered Nd-Fe-B

Sintered Nd-Fe-B magnets have been widely used in electronic devices for their remarkable magnetic properties.However,Nd-Fe-B magnets are sensitive to the grain boundary corrosion because of the large difference of electrode potential between the matrix and intergranular phases.The Nd-rich phase is quite lively,which will react with H2 O in hot and humid environment,resulting guain boundary stess,expanding the volume of grain boundary and damaging the grain boundary phase.These reasons have limited the application of sintered Nd-Fe-B magnets in a lot of important fields.Corrosion resistance of Nd-Fe-B magnet is closely related to the microstructure of grain boundary phase.At present,modifying the phase of Nd-rich phase is one of the most effective methods to improve the corrosion resistance.In this paper,in order to improve the magnetic properties and corrosion resistance of sintered Nd-Fe-B magnets,the Nd-Fe-B magnets were prepared by the double-alloy powder mixed method with Mg nano-powders.Using scanning electron microscope(SEM),X-ray diffraction(XRD)and AMT-4 magnetic measurement device to analyze microstructure and magnetic properties of sintered Nd-Fe-B magnets(PrNd)29.9Dy0.1B1Co1Cu0.15Febal(wt.%).Mg nanopowders addition amounts were 0.0wt%,0.1wt%,0.2wt%,0.3wt% and 0.4wt%.The result showed that addition amount of 0.1wt% Mg,Hcj reached the maximum value of 999.1kA/m,Br reached 1.436 T,(BH)max reached 396.9kJ/m3 and magnet density is 7.42g/cm3,which increased 0.27%.The magnetic properties increase is related to the microstructural modification of grain boundaries and the magnet density.The polarization curves were investigated by electrochemical workstation.Their corresponding corrosion potential Ecorr and corrosion current density icorr were acquired from the polarization curves.Y coordinate for the corresponding corrosion potential,the intersection of the anode curve and the corrosion potential of abscissa for the corresponding corrosion current density.With Mg nano-article addition form 0.0wt% to 0.4wt% in 0.005% H2SO4 solution Ecorr increases form-0.618 V to-0.470 V,respectively,and icorr decreases form 193.1A/cm~2 to 46.5A/cm~2 correspondingly.Accelerated corrosion test was performed by placing cubic samples hot/humid atmosphere for various times.After 96 h corrosion in hot/humid atmosphere,the quantity of mass loss changed from 42.3 to 5.3 mg/cm~2 with the Mg addition from 0.1wt% to 0.3wt%.Which indicates that additive Mg of magnets can improve the corrosion resistance of sintered Nd-Fe-B magnets.Further investigation reveals that the better magnetic properties are relate to the formation of Mg-Nd intergranular phase.