Sintered Ndfeb Permanent Magnet Chemical-plated Anti-corrosion Studies

Permanent magnets based on the elements neodymium, iron and boron (NdFeB) are known to possess outstanding magnetic properties with high remanence, high coercivity and high energy products. Despite the many benefits of employing NdFeB magnets, the sintered NdFeB magnets have been in part held back by their poor corrosion resistance.As part of efforts to overcome this problem, Ni-P alloy was electrolessly plated on the surface of the NdFeB as the protective film. The effects of various pretreatment processes and electroless plating bath on coating properties have been investigated. Effects of added rare earth (RE) and ultrasonic agitation in plating bath on the properties of the resulting Ni-P deposits have also been studied.Results have shown: (DA better finish is generated by degreasing with alkaline cleaning agents and deoxidizing with 10%(vol) nitric acid and 5%(wt) concentration of urea; (2) It is proved that NdFeB base can't be electrolessly plated directly with the acid plating bath, otherwise, the NdFeB will be badly deteriorated and the plating bath will be out of effect;.(5)The composite deposit was obtained from the acid plating bath based on electroless pre-deposite in the presence of alkaline plating bath. The results have shown that the composit coating is very effective for improving corrosion resistance; (4)Electrolessly plating Ni-P deposits were prepared for the sintered NdFeB magnets under 40 KHz frequency ultrasonic field. The results of the deposits surface morphology show that the formed microstructure is more compact fine in presence of ultrasound field; (5)The electrochemical measurements exhibit that the corrosion resistance of the Ni-P coatings is greatly improved by the addition of Ytterbium element. Meanwhile, the microhardness of the coating is obviously enhanced after introduction of Ytterbium.