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Introduction of surface phosphating of NdFeB (purpose, principle, process flow)

We all know that NdFeB magnets are easily oxidized and easily corroded. Usually, the surface will be protected by a layer of coating. Commonly used, such as galvanized, nickel plating, and There is also a coating customer that uses less, that is, phosphating, Xiaofu contact many customers of magnets, but there are not many customers who require phosphating. Today, I will introduce the relevant knowledge of neodymium magnet phosphating.
 
The following picture shows the phosphating NdFeB curved magnet.
 
Why do phosphating? The purpose of phosphating:
 
There are two purposes for the phosphating surface treatment of sintered NdFeB permanent magnets. The first is to prevent corrosion as a process, and the second is to improve the surface epoxy infiltration.
 
1, process anti-corrosion
 
Due to the low density and porosity of the sintered NdFeB surface, the exposed magnets will oxidize in the air, which we also call corrosion. Therefore, when the NdFeB magnet is too long in turnover and storage, and the subsequent surface treatment method is not clear, it is necessary and effective to use the phosphating process for simple anticorrosion treatment.
 
The phosphating process is simple, no equipment investment is required, and the phosphating production process consumes less, mainly acid, alkali and phosphating solution, and the production cost is low. As the process anticorrosion does not significantly increase the production cost of the magnet. And can avoid magnet loss during storage period. There is high rate of return. After phosphating, the product has uniform color and clean surface. It can be vacuumpacked, which greatly prolongs the storage time. The storage method is superior to the previous oil immersion and coating oil storage methods. The complete phosphating film can resists oxidative corrosion of the normal atmosphere. The subsequent surface treatment of the phosphatized magnet product is very easy. The phosphating film can be completely removed by simple pickling, and it will not adversely affect the subsequent surface treatment (such as galvanizing, nickel plating, etc.), and the subsequent surface treatment process can be completed at any time.
 
2, improve the wetting performance
 
Some NdFeB magnets require epoxy bonding, painting, etc. The bonding force of epoxy, lacquer and other epoxy organic materials requires a good wetting property of the substrate. Phosphating film and epoxy organic matter have good wetting property, so it is necessary to use phosphating process to improve the wetting property of NdFeB magnet surface. Good wetting properties ensure the bonding of epoxy glue, epoxy paint and magnet.Principle and process of phosphating:
 
The process of phosphating the surface of the magnet is: degreasing→water washing→acid washing→water washing→surface adjustment→phosphating treatment→closed drying.
 
The degreasing and pickling treatment is the same as the preplating treatment. The surface adjustment is a special surface treatment for the surface of the NdFeB magnet to adapt to the formation of the phosphating film. The surface adjustment of NdFeB magnets is generally immersed in a weak acid to improve the alloy composition on the surface of the magnet to achieve the purpose of facilitating the formation of the phosphating film. The phosphating process is currently mainly produced using commercial phosphating solutions. Commercialized phosphating solution is divided into zinc, iron, manganese, binary, ternary, and multi - variety. Each system has its own advantages and disadvantages. Therefore, in the application of NdFeB phosphating, each magnet manufacturer will use the variety that it considers appropriate due to the purchase price and the effect of use. Some NdFeB products require phosphating after galvanizing. Phosphating after galvanizing should use zinc phosphating solution or zinc-containing multi-phosphorizing solution.
 
The phosphating process is divided into three types: high temperature, medium temperature and normal temperature. The high temperature process generally has a thick film layer, a high density of the phosphate film, and a large thickness; a normal temperature process generally has a thin film layer; and a medium temperature process is between the two. Most of magnetic material manufacturers use a normal temperature process, but the normal temperature process also requires temperature control to ensure temperature stability (15 ° C -35 ° C).
 
Rusting problem after phosphating:
 
Some readers have responded that there is still rust in the magnetic material after phosphating. There are many reasons for this phenomenon. For example, the concentration of the phosphating agent in the phosphating bath is not enough, resulting in the phosphating film being too thin or loose. It is not good to insulate the air; it is not washed clean after phosphating, or the acidity of the washing tank is too high, causing acidic substances to remain on the magnetic material, and the acid solution destroys the phosphating film and causes rust; in addition, it should be checked whether the oil removal is thorough. The removal of oil will also affect the phosphating effect. In order to ensure the phosphating effect, special attention should be paid to the phosphating solution distribution ratio during the phosphating process to ensure proper temperature; the phosphating time is controlled at 10-15 minutes; By mounting or reducing the load, it is ensured that there is a certain gap between the magnetic materials, and the phosphating is sufficient.
 
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