Improvement on corrosion resistance of sintered Nd-Fe-B with bilayer Al/Cr thin films

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 pursuing 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 x 10(-7) A/cm(2) 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 mechanical protections for Nd-Fe-B magnets.

Automated summary

This article investigates the influence of surface coating treatment on the corrosion resistance of Nd-Fe-B permanent magnets, and proposes the optimum anti-corrosion performance of bilayer thin Al/Cr films. The film effectively prevents the penetration of corrosive ions and has no significant impact on the magnetic and mechanical properties.