Enhanced corrosion resistance of NdFeB magnets via arc ion plated CrAlN coatings: Microstructure optimization and property evaluation

The susceptibility to corrosion limits the application of NdFeB magnets in harsh environments. In this study, CrAlN coating was prepared on NdFeB magnets by means of multi-arc ion plating technology, aiming to enhance their corrosion resistance by optimizing the coating structure. The effect of bias voltage on the microstructure, phase composition and corrosion resistance of CrAlN coatings during the arc ion plating deposition process was investigated. Concurrently, the influence of coating preparation on the magnetic and mechanical properties is evaluated. Results show that the arc ion plated CrAlN coating can effectively improve the corrosion resistance of NdFeB magnets without degrading their magnetic properties. In particular, the coating deposited at a moderate bias voltage has a dense structure and suitable surface roughness, which prevents the penetration of corrosive substances. The structurally optimized CrAlN coating significantly raises the corrosion potential of the magnets and reduces the corrosion current density. The corrosion current density of it is as low as 3.255 × 10⁻⁶ A/cm², which is merely 14.4 % of that of the bare NdFeB magnets. No obvious corrosion rust appear on the coated-magnets after been immersed in 3.5 wt% NaCl solution for 24 hours. Furthermore, the CrAlN coating increases the hardness of NdFeB magnets from 628.9 to 1347.4 HV_0.5, ensuring that the magnets possess excellent mechanical properties. This study has confirmed the potential of the CrAlN coating in improving the corrosion resistance of NdFeB magnets.