Effect Of Grain Boundary Addition Of Al-based Alloy Nanopowder On The Performance Of Sintered Nd-Fe-B

The sintered Nd-Fe-B permanent magnets are widely used in various fields in today’s society advocating sustainable development and green energy,such as magnetic refrigeration,medicine,green energy industry generators and other directions.However,factors such as the susceptibility of magnets to corrosion and low coercivity limit the application,so it is urgent to improve their performance.It was found that the key to the performance of sintered Nd-Fe-B is the microstructure,especially the relationship between the main phase and the grain boundary phase.Therefore,the improvement of the microstructure of magnets by transition metal-rare earth alloy nanopowder was investigated by grain boundary addition method.In order to improve the microstructure of Nd-Fe-B,the corrosion resistance of Nd-Fe-B is improved while the magnetic properties are maintained,preparation of Ho,Cu,Al nanopowders and Ho-Al alloy and Cu-Al alloy nanopowders by DC arc method.The Ho,Al,Cu,Al nanopowders were evenly mixed by vacuum mixer to obtain Ho/Al,Cu/Al co-added nanopowders,and then Ho/Al,Ho-Al,Cu/Al and Cu-Al nanopowders were treated with sintered（Pr Nd）₃₀Dy Fe_66.24Co Al_0.6Cu_0.2B_0.96magnetic powder at different ratios（x=0,0.2wt%,0.4wt%,0.6wt%,0.8wt%）,respectively.Finally,the modified Nd-Fe-B magnets with different composition and content of grain boundary addition were obtained and characterized and tested.The results showed that Ho-Al alloy nanopowder and Cu-Al alloy nanopowder were successfully produced by the DC arc method.Ho₇₀Al₃₀alloy nanopowder had better corrosion resistance than Ho nanopowder.The performance of Nd-Fe-B magnets was compared with that of Nd-Fe-B magnets with the same atomic ratio of Ho/Al mixed nanopowder,and the remanence of Nd-Fe-B magnets with Ho-Al alloy nanopowder was reduced less than that of Nd-Fe-B magnets with Ho/Al mixed powder,and the coercivity was changed little.However,the coercivity of the magnets increased with the addition of Ho-Al,and the addition of 0.8wt%magnets improved 22.8%compared to 0 added magnets.The corrosion resistance of the magnets was the strongest for each of Ho/Al co-added and Ho-Al alloy nanopowder added at0.2wt%.The weight loss at 96 h of weight loss corrosion for Ho/Al co-added magnets added at0.2wt%was 36.2%of that for 0 added magnets,the weight loss for Ho-Al alloy magnets added at 0.2wt%was 30.7%of that for 0 added magnets.Based on the above conclusions,the addition of appropriate amount of Ho-Al alloy nanopowder is superior to Ho/Al co-added nanopowder magnets,effectively isolating the main phase to play the role of demagnetization exchange coupling,and achieving the purpose of maintaining magnetic properties while improving corrosion resistance.Cu₂₀Al₈₀,which contains the highest content of binary alloy phase Cu Al₂,was chosen to be added to Nd-Fe-B.The addition of Cu/Al co-added and Cu-Al alloy nanopowder both played the role of remanence reduction coercivity increase,and the magnet coercivity was increased by 18.1%compared with 0 added magnets when Cu-Al alloy nanopowder was added at 0.8wt%.Among them,the corrosion resistance of the magnet was the strongest when Cu/Al co-added nanopowder was added in 0.4wt%,and the weight loss of the magnet after 96 hours of weightless corrosion was 42.5%of that of the magnet added in 0.When Cu-Al alloy nanopowder was added in 0.2wt%,the corrosion resistance of the magnet was the strongest,and the weight loss of the magnet was 40.2%of that of the magnet added in 0 after 96 hours of weightless corrosion.It is shown that the addition of appropriate amount of Cu-Al alloy nanopowder has better magnet performance than Cu/Al co-added nanopowder,and optimizes the microstructure of the magnets.The low melting point of Cu and Al elements makes the liquid phase sintering of the magnets completely dense which limits the corrosion propagation path and inhibits the intergranular corrosion process to achieve the purpose of maintaining magnetic properties and improving corrosion resistance.