Preparation And Properties Investigation Of Bonded NdFeB Magnet

In recent decades, the market demand of the bonded NdFeB magnets has grown notably because of high magnetic and mechanical performance and good machinability. So it is necessary to investigate the effects of preparing process on properties of bonded magnet and to optimize its preparing process parameters. In this thesis, the melt-spinning NdFeB powder bonded magnets have been prepared with different process parameters, their magnetic properties and compressive strength have been measured, and their microstructure has been investigated by XRD, SEM. Consequently, the effects of preparing process parameters on the properties of magnets have been discussed.It is shown that binder content of bonded magnet is one of the most important factors for magnetic properties. More or less binder content influences magnetic properties directly. As binder content low, magnetic powder is not folded completely, resulting to lower magnetic properties and compressive strength. With the increase of binder content, the magnetic properties and compressive strength of bonded magnet increased gradually. When content of binder is 2.5wt%, the best magnetic properties have been obtained. Beyond this value, the properties of magnet decrease due to non-magnetic and quite low intensity of binder.In molding process, molding stress decides magnet density, magnetic property and compressive strength. Magnet density and magnetic properties is high along with molding stress. However, beyond 20 kN, the phenomenon of powder transmogrification appears and the powder crystal has been broken, so properties of bonded NdFeB magnet reduces obviously.The bonded magnets, which have not been thermoset, have a lower compressive strength and can't be used in practical. Thermosetting process is in favor of not only pervasion of binder, but also soakage of powder. Crosslinking reaction correlates to temperature. Below range of temperature, the magnetic property will not get well because of thermosetting imperfection. Beyond temperature, density and intensity of bonded magnet will reduce resulting from rapidness of thermosetting and aging of binder. Properties of bonded magnet are wellwhen 150℃for 2h.By orthogonal experiment method, the effects of binder content, molding stress, thermosetting time and temperature on properties of magnet have been studied. The results show that the molding stress should be high, thermosetting time is the least influencing factor on magnet properties, and temperature should low, binder content decides the properties of bonded magnet directly.By experiment, the best preparing parameters and properties have been obtained as follow: binder content 2.5wt%; molding stress 20kN; thermosetting at 150℃for 2h. Obtained properties of bonded magnet as follow: density 5.54g/cm³; B₄=0.594T; H_cj =751kA/m; (BH)_m =55kJ/m³; compressive strength is 188MPa.