Enhancing corrosion resistance of Nd-Fe-B magnets with amorphization Ni-P coatings

Nd-Fe-B permanent magnets, due to the unique phase structure, demand exceptional corrosion resistance. Electrodeposited nickel-phosphorus (Ni-P) coatings are recognized for their superior anti-corrosion performance, but the performance of electrodeposited Ni-P coatings with different crystallinity varies considerably from process to process. In this study, we propose a strategy to grow Ni-P coatings that exhibit varying crystallographic orientations and degrees of crystallinity. Meanwhile, the differences in structure, morphology, corrosion resistance, and mechanical properties between crystalline and amorphous Ni-P coatings were systematically investigated. The results show that the crystalline Ni-P alloy coating predominantly forms on the Ni(111) crystal plane, with poor surface topographic flatness. In contrast, the amorphous Ni-P coating demonstrates better surface topographic flatness. The crystalline Ni-P alloy coating exhibits a corrosion potential of −0.63 V, a corrosion current density of 5.6 × 10⁻⁷ A cm⁻², and a hardness of 583HV. In comparison, the completely amorphous Ni-P alloy coating shows an improved corrosion potential of −0.38 V, an exceedingly low corrosion current density of 9.5 × 10⁻¹⁰ A cm⁻², and an increased hardness of 622HV.