Similar to phosphating, ndFeb passivation is a chemical method to form a protective film on the surface of the workpiece to prevent corrosion of the workpiece. Surface chemical conversion film technology is a common means of surface treatment. At present, the surface chemical conversion film treatment of NdFeb mainly USES phosphating technology. Most of them are common zinc or iron series phosphating. Meanwhile, a large number of phosphoric acid and phosphate compounds are used in phosphating process, which is easy to produce phosphorus pollution, resulting in eutrophication of water and other adverse consequences, and the production process is environmentally unfriendly. Compared with phosphating agents, passivating agents are simpler in composition and do not contain phosphoric acid and phosphate compounds, so they are more environmentally friendly.
NdFeB passivation process is generally: oil removal → washing → ultrasonic washing → acid washing → ultrasonic washing → pure water washing → pure water washing → passivation treatment → pure water washing → pure water washing → dehydration → drying.
In addition to the oil
Oil removal can only remove the ndFeb surface grease, dust, sweat and metal particles attached to it. It cannot remove the rust on the magnet. Oil stains on the surface of NdFeb are caused by the processing of materials, such as anti-rust grease used in storage and transportation, cutting fluid contacted by parts during cutting.
Neodymium iron boron must be cleaned of oil before further surface treatment, otherwise it will affect the quality of surface chemical transformation, electroplating or coating. Because the source of oil pollution is wide, many kinds, the degree of pollution varies greatly, so the problem of removing oil is very complicated. In order not to cause corrosion and subsequent residue in the degreasing process, the degreasing agent with low free alkalinity and total alkalinity is used as far as possible.
The purpose of pickling is to remove the residual black ash and rust on the surface of NdFeb. Generally, 2%~4% nitric acid is used for acid lotion, and the time is 0.5~ 2.0min. High acid concentration and long pickling time are unfavorable to magnets.
The passivation treatment method is to put the magnet in a container containing passivation solution, soak or spray it for a period of time or use the magnet as the anode for electrification polarization, then passivation can be realized, that is, a passivation film can be formed on its surface. As an important means of surface corrosion prevention, passivation is widely used in many metals, especially in aluminum, zinc, cadmium, tin and magnesium and their alloys.
The traditional passivation treatment mostly USES chromate and chromate as the treating agent, which is called chromate passivation. The chromate conversion film formed on the metal surface after the treatment has a good anticorrosion and protection effect on the matrix metal. As a separate protective film, passivation treatment is simple, practical and low cost. It was widely used in the early stage of development of NdFeb. But it is the fatal weakness of chromium containing toxic Cr (Ⅵ), the harm of human body and environment has prompted people to actively carry out effective alternative technology research. In recent years, our country has many passivator patent, there is a kind of NdFeB Magnet passivator, including: oxalic acid, surfactant and complexing agent, its composition is simple, and at the same time have the function that degreasing, derusting and passivation, and without the use of phosphoric acid and phosphate compound, is a kind of more convenient, environmental protection passivating agent of ndfeb magnet.
In recent years, the corrosion resistance of NdFeb conversion film has become more and more demanding, and it is difficult to meet the requirements of passivation technology alone. The common process is to use the composite conversion film technology, namely phosphating and passivation, by filling the pores of the phosphating film, effectively improve the corrosion resistance of the composite conversion film.