Phosphating treatment of sintered NdFeB (neodymium-iron-boron)

Everyone knows that sintered NdFeB magnets are prone to oxidation and corrosion. Over time, their magnetic properties can deteriorate. Therefore, before fully unleashing their potential, they need meticulous care. We've previously uncovered the top-secret techniques of electroplating, but besides electroplating, there's a plethora of trendy methods such as chemical plating, electrophoretic coating, and phosphating. Today, let's take stock of the cool maneuvers of phosphating.

Purposes of phosphating treatment:

Firstly, phosphating sintered NdFeB permanent magnets serves two purposes: corrosion prevention and smoother epoxy coating.

1. Corrosion prevention:

Because the surface of sintered NdFeB magnets is porous like a sponge, they tend to rust when exposed to air, which can be quite embarrassing. So, if you're unsure about the next steps in care, phosphating is a simple and effective choice, both cost-saving and efficient. The phosphating process is straightforward, requires minimal materials, and has low costs. It can prevent loss of magnets during storage, yielding high returns. Products after phosphating look comfortable and have a remarkably smooth surface, suitable for direct vacuum packaging, with a much longer lifespan compared to oil coating storage. Moreover, a perfect phosphating film can resist conventional oxidation corrosion, making subsequent treatments a breeze—just rinse with acid, and galvanizing or nickel plating is easily accomplished.

2. Improving epoxy impregnation performance:

Some magnets need to combine with epoxy adhesives or coatings, for which phosphating provides an excellent foundation. The bond between the phosphating film and epoxy adhesive is exceptionally strong, making phosphating an essential step if you want epoxy adhesives or paints to adhere tightly to the magnet.

Principles and operating steps of phosphating:

Phosphating magnets is no child's play; it involves degreasing, washing, acidifying, and more before it can spruce up.Degreasing and pre-treatment before electroplating are similar. Then, some special treatment is needed on the magnet surface to ensure robust phosphating film growth. Typically, a weak acid bath is used to make the surface alloy more suitable for film growth.

Nowadays, phosphating solutions are commercialized, available in various types—zinc-based, iron-based, manganese-based, and more—each with its own strengths. Therefore, in phosphating production, manufacturers need to carefully consider factors like price and effectiveness to choose the most suitable one. Some products require zinc plating before phosphating, so a phosphating solution containing zinc must be used.

Phosphating processes are divided into high, medium, and low grades, with high-grade films generally thicker, denser, and more robust, while low-grade films are thinner. Most manufacturers use medium-grade phosphating, but temperature control is crucial to prevent bubbling.

Rust issues after phosphating:

Some readers have complained that their magnets still rusted after phosphating, which can result from various factors such as too dilute phosphating solution, too thin or loose film that cannot resist oxygen, inadequate rinsing during washing, or excessively acidic washing solutions damaging the film. Moreover, incomplete degreasing can also affect the results.Therefore, to achieve successful phosphating, attention must be paid to the composition of the solution and maintaining the appropriate temperature; phosphating time should not exceed 15 minutes; hanging or reducing the loading amount to ensure adequate spacing for uniform phosphating is essential.

Now, isn't phosphating much clearer?