Fabrication and corrosion behavior of Ni-Cu (graphene) composite coating on NdFeB magnet surface

Although NdFeB magnets demonstrate superior magnetic performance, their limited corrosion resistance restricts their practical applications. This study employed pulse current electrodeposition to fabricate a Ni-Cu Graphene (Gr) composite coating on sintered NdFeB magnets and investigated its corrosion behavior and underlying corrosion mechanisms in various environments. Immersion tests in 3.5 wt.% NaCl solution and Highly Accelerated Stress Testing (HAST) confirmed that Gr co-deposition significantly enhances the corrosion resistance of the coatings.​ The composite deposition of Gr facilitates the formation of a preferred orientation of the coating's crystal planes, effectively enhancing the degree of (111) plane orientation, reducing the density of active sites at grain boundaries, and slowing down the corrosion rate.​ Furthermore, the co-deposition process establishes continuous barrier networks within the coating, effectively blocking the penetration of corrosive media such as Cl⁻, O₂, and H₂O.​ Additionally, the highly conductive Gr enhances charge transfer efficiency, accelerating the formation of the passivation film. This enables rapid reduction of Ni²⁺ to metallic Ni or stable NiO, thereby strengthening the self-healing capacity of the coating's passivation layer.​ These findings contribute to the understanding of nanoparticle-enhanced corrosion resistance in coatings and provide insights into the underlying microscopic mechanisms.