To enhance the corrosion resistance of neodymium-iron-boron magnets, surface treatment is typically required. Common surface treatment methods for neodymium-iron-boron magnets include phosphatization, electroplating, electrocoating, and vapor deposition. Passivation of neodymium magnets involves forming a protective layer on the magnet surface through chemical means to achieve corrosion prevention.

The passivation process for neodymium-iron-boron magnets typically includes: degreasing → water washing → ultrasonic water washing → acid washing → water washing → ultrasonic water washing → pure water washing → passivation treatment → pure water washing → dehydration → drying.

1. Skimmed

Neodymium-iron-boron magnets can only remove oils, dust, sweat stains, and adhered metal shavings from the surface, but not rust. The oil污 on the surface of neodymium-iron-boron magnets is introduced during the material processing, such as the anti-rust oil used to prevent rust during storage and transportation.

Neodymium-iron-boron magnets must be thoroughly cleaned of surface oil before further surface treatment. Due to the wide range of sources and varied types of oil污, as well as the significant differences in contamination levels, the degreasing process is quite complex. To avoid corrosion and subsequent residues during the degreasing process, it is recommended to use degreasers with lower free alkali and total alkali content.

2. Pickling

The purpose of pickling is to remove the black soot and rust residues from the surface of neodymium-iron-boron magnets. The pickling solution typically uses 2% to 4% nitric acid, with a duration of 0.5 to 2.0 minutes. Higher acid concentration and extended pickling time are detrimental to the magnets.

3. Passivation Treatment

The passivation process involves placing a magnet in a container filled with passivation solution, soaking for a period of time to achieve passivation, which is to form a passivation film on its surface. Passivation, as an important surface corrosion prevention treatment, is widely used in many metals, especially aluminum, zinc, cadmium, tin, magnesium, and their alloys.

Traditional passivation processes mostly use chromic acid and chromates as treatment agents, known as chromate passivation. The chromate conversion film formed on the metal surface after treatment has excellent corrosion resistance for the base metal.

In recent years, there has been a growing demand for the corrosion resistance of neodymium iron boron magnets, and the traditional passivation technology alone is no longer sufficient to meet these requirements. The commonly used process involves the application of composite conversion coating technology, which entails phosphating followed by passivation. By filling the pores of the phosphating film, the corrosion resistance of the composite conversion coating is effectively enhanced.