Study On Strengthening And Toughening Of Sintered NdFeB Permanent Magnets

Sintered NdFeB has excellent magnetic properties with low price while the strength and toughness are poor which result in poor machinability, and it is easy to be broken. So they can not be used in areas with impact. Up to now, there is quite few studies on strength and toughness of this materials, and the mechanism of facture is not well determined. So the ways to improve the strength and toughness of this materials are quite eyeless.In this dissertation, the magnets were prepared by powder metallurgy. Powders of Ag were added during ball milling, and powders of Al and Ti were added separately and jointly during ball milling, while Al and Ti were jointly added during melting. The samples were sintered for 0.5h at 1090℃. The magnetic properties and impact toughness were measured and the fracture surfaces were observed by SEM. It follows that the fracture behaviour and the impact toughness and magnetic properties,especially the coercivity, were dramaticly different according to the ways elements addition.The impact toughness of the magnets could be improve with appropriate alloying elements addition during ball milling while there was no visible changes to the fracture behaviour, and the coercivity of magnets with Al and Ti was significantly enhanced. The impact toughness of the magnets with 0.05%Ag was 70% higher than that of commercial N35 magnets without magnetic properties deterioration. And there was no visible changes to fracture behaviour of these magnets. The impact toughness could be prominently improved by Ag mainly because of the depressing of grain growth during the sintering, and some granuliform Nd-rich phase appeared.The impact toughness of the magnets with Al and Ti during melting could be prominently improve, and the fracture behaviour of the magnets was visibly changed, but the coercivity of magnets depended on the proportion of Al and Ti. The impact toughness of Nd15.5Fe76.5Al1Ti0.5B6.5 magnets was 51.8% higher than that of N35 magnets with little change of the magnetic properties. The fracture behaviour of these magnets was changed markedly, the...