Research On Improving The Performance Of Sintered NdFeB Magnet By Magnetron Sputtering Coating And Vacuum Anealling

The excellent energy product and high intrinsic coeroivity of NdFeB permanent magnetic material brought revolutionary changes in its applications. In our country, the NdFeB industry has become a pillar industry, and is playing a more and more important role in development of our national economy. Sintered NdFeB magnetic material is widely used in electronic information, automotive industry, medical facilities, energy and transportation, industrial energy-saving motor, energy-saving household electrical appliances, wind power generation. The existing sintered NdFeB magnetic material has two major weaknesses, such as poor heat-resistance and corrosion resistance, which limited its more widely used. So how to improving heat-resistance and corrosion resistance of the sintered NdFeB magnet so as to meet a higher application request, become an urgent problem in the NdFeB industry.The present research wedded the new trend of NdFeB industry. In this paper, Al and DyAl alloy thin films were deposited on the sintered NdFeB magnets’ surface by magnetron sputtering, which wedded with the vacuum heat treatment and diffusion process, presenting a prospective exploratory work. The microstructure and composition of the films and the samples were characterized by SEM, EPMA, and X-ray diffraction (XRD). The magnetic performance and the corrosion resistance of the magnets were characterized by Polarization curve, PCT weight loss test, salt spray testing and NIM-10000H measurement device for bulk rare earth permanent magnet. The influences of magnetron sputtering wedded with heat treatment process on the microstructure, magnetic performance, corrosion resistance and heat-resistance of magnets were investigated. This paper offers a new path for development of NdFeB magnetic material in our country, and has a practical significance. Al metal films were prepared on the NdFeB magnets’surface by DC magnetron sputtering. The samples with Al films went through vacuum heat treatment. The influences of coating process, temperature and time of treatment on the composition and microstructure of the films, and corrosion resistance of magnets were investigated. It’s found that the corrosion resistance of magnets was promoted with the increase of Al film’s thickness, and corrosion resistance of magnets was improved remarkably in a preferable heat treatment parameter,650℃x10min.DyAl alloy thin films were prepared on the NdFeB magnets’surface by DC magnetron sputtering. Then, the samples with DyAl films went through an800℃x6h vacuum diffusion and a900℃x2.5h+490℃×5h aging treatment. The microstructure, magnetic performance and corrosion resistance of magnets were investigated. It’s found that through the process aboving, the intrinsic coeroivity (Hcj), which was improved by14.7%maximumly, heat-resistance and corrosion resistance of the magets were improved remarkably. The diffusion behavior of Dy, Al elements in the magnets was researched.The machined magnets went through the vacuum annealing by industrial vacuum sintered furnace. The influences of heat treatment process on the grain microstructure, train, subgrain dimension and magnetic performance of magnets were investigated. In the investigations, a tissue with thin net structure of Nd-rich phase in the grain boundary was found under20-30μm to the magnet’s surface for the first time, which played an important role in the recover and promotion of machined magnets performance.