The Study Of Electroless Plating Of Ni-Cr-P/Ni-P Complex Coating On Nd-Fe-B Magnet

Nd-Fe-B magnet, which possesses excellent magnetic properties andwas discovered by Japan and the USA in 1983, is a new type of permanentmagnetic material. Since the discovery, its research and application hasbeen hot spots of the study of magnetic materials. However, its poorcorrosion resistance limits its application range. To improve the corrosionresistances of Nd-Fe-B type magnets, lots of attempts have been done,such as: other alloy elements additions and surface coatings.Among all surface coatings, amorphous Ni-P coating, whichpossesses more excellent mechanical, magnetic and anti-corrosionperformance over the crystal materials, may be one of the best. However,along with the development of science and technology, Ni-P coating cannot continue to fulfill the daily elevated anticorrosion request of modernindustry on Nd-Fe-B magnet. By adding chromic salt into the platingsolution of Ni-P coating, Ni-Cr-P coating can be fabricated. The process issimple and convenient, the coating also show better corrosion resistancethan Ni-P coating. But Ni-Cr-P coating also has its downsides, like lowercompactness and higher porosity rate. To combine the advantages of theseto coatings, the electroless plating technics of Ni-Cr-P/Ni-P complex coating is studied in this paper.First, the perpendicular experiment is used to select the opticaltechnical parameters of both alkaline and acidic Ni-P electroless plating.Structure analysis and performance testing shows that the Ni-P coating hashigh compactness and low porosity rate. It also shows great corrosionresistance in alkaline medium, but not so well in acidic medium.Then the perpendicular experiment is used to select the opticaltechnical parameters of Ni-Cr-P electroless plating. The effects oftemperature, pH valve and chromic salt concentration on depositionvelocity and corrosion resistance are also discussed. Structure analyses andperformance testing shows that the Ni-Cr-P coating has amorphousstructure, high compactness and low porosity rate.Finally, the structure and performances of several different complexcoating are studied and tested, also compared to the Ni-P coating. Theresults show that, the complex coating prepared by Ni-Cr-P electrolessplating (15min) and Ni-P acidic electroless plating (45min) has amorphousstructure, simple process and better anticorrosion performance in bothalkaline and acidic medium. A logical solution of the anticorrosion ofNd-Fe-B magnet has been offered.