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Corrosion induced irredeemable magnetic loss of Nd-Fe-B permanent magnets is of great concern in industrial applications. Surface coating treatment provides an effective approach for improving corrosion resistance, but the coating induced magnetic strength deterioration should also be taken into account, in addition to the pur- suing of anti-corrosion performance. Herein, bilayer thin Al/Cr films were prepared on Nd-Fe-B magnets, the corrosion behavior and mechanical properties of Nd-Fe-B were investigated. The results revealed that Al/Cr film with 510 nm thickness provided the best anti-corrosion performance in 3.5 wt% NaCl solution, offering a corrosion current density of 2.08 × 10-7 A/cm2 which was two orders of magnitude lower than that of bare Nd- Fe-B magnets. Bilayer structured Al/Cr film with Cr2O3 passivation layer can effectively prevent the penetration of the corrosive ions. In addition, deposition of Al/Cr film on Nd-Fe-B magnets gave no significant impact on the magnetic properties, furthermore, the hardness and Young’s modulus were both improved. The present work demonstrated that Al/Cr films have great potential to be utilized for providing effective corrosion and me- chanical protections for Nd-Fe-B magnets.

Material properties of permanent magnet in the magnetic fluid seal are important factors that determine the sealing effect. However, the relationship between the magnetic properties of permanent magnet and the failure-pressure has not been studied quantitatively in the available research. In this work, the relationship between material properties of permanent magnet and the failure-pressure of magnetic fluid seal was obtained from theoretical analysis and numerical simulation. The permanent magnet was changed in materials to calculate the failure-pressures of a typical magnetic fluid seal. The result shows that the failure-pressure of magnetic fluid seal grows with the maximum magnetic energy product of permanent magnet increases at the beginning, whereas there is a turning point. After that, the failure-pressure decreases as the maximum magnetic energy product increases.