Electroplating and plating types of neodymium magnets

The anti-corrosion performance is determined by the type of electroplating and plating layer of neodymium magnets

Due to the structure and chemical properties of neodymium magnets,they will rapidly oxidize in air.Experimental results show that a 1cm³ sintered neodymium magnet will be completely oxidized and corroded in air at 150℃ for 51 days.Secondly,electroplating can form a tough protective layer on the surface of the magnet,effectively reducing the damage caused by collisions and friction.Moreover,the plating can also improve the smoothness of the magnet,thereby improving its appearance.Therefore,in order to prolong the service life of neodymium magnets as much as possible,we usually use electroplating to protect them.

1. Treatment before electroplating

①Chamfering

Chamfering is to grind the edge of the magnet to a certain arc and remove the burrs caused by machining.This can increase the contact area between the edge of the magnet and the plating layer, increasing the adhesion of the plating layer.Chamfering can also effectively eliminate stress concentration areas on the edge, reducing the risk of cracking due to stress concentration during the use of neodymium magnets.

② Sealing the hole

As a powder metallurgy material, neodymium magnets have many tiny pores on their surface.Before electroplating, the magnets need to be acid-washed.If the sealing treatment is not performed, acidic substances will remain in the pores of the neodymium magnets.After about half a year of corrosion, the neodymium magnets will appear powdered and peeling.Therefore, in order to obtain a good coating, a sealing agent must be used for sealing treatment before electroplating.

③Curing

When curing in an oven, set the temperature to about 60°C for 30 to 40 minutes to achieve the curing effect.If you choose to leave it at room temperature, make sure to leave it for more than 2 hours.

④Degrease

Neodymium magnets have strong oil absorption properties and can be treated with neutral or weakly alkaline degreasing agents.

⑤Acid washing

The main purpose of acid pickling is to remove oxides, rust, and impurities on the surface of neodymium magnets to ensure a clean surface, thereby improving the adhesion and quality of the plating layer.This process typically involves treating the surface with dilute nitric acid solution or weak organic acid for a short period of time.However, if the treatment method is not appropriate, it may cause corrosion of the neodymium magnet.To avoid this, a corrosion inhibitor must be added during the acid pickling process.

⑥Activation

Put the magnet into the activator solution for soaking.After activation treatment, the surface of the neodymium magnet becomes more active, and can better react with the metal ions in the plating solution to form a uniform and dense plating layer.

⑦Cleaning

Cleaning is required after every processing step that leaves corrosive residues.Since the advent of high-power ultrasonic cleaning machines in industrial production, the processing flow before electroplating has become easier.Ultrasonic cleaning can almost completely remove the dirt and corrosive substances remaining in the pores of magnetic materials.This allows some low-end magnetic materials with low requirements to be processed simply and without the need for specialized chemical reagents, greatly reducing processing and material costs.

The quality of neodymium iron boron electroplating is directly affected by its pre-treatment effect.After the above-mentioned treatment steps, we can ensure that the surface of the magnet reaches the ideal state for electroplating.However, if any link in the pre-treatment stage is not thoroughly cleaned, it may lead to potential defects in the electroplated product, such as blistering and peeling of the plating layer.

2. Electroplating

Electroplating

Electroplating mainly uses electrolytic deposition technology, with neodymium magnets as the anode and metal (such as nickel or zinc) in metal salt solution as the cathode.During the electroplating process, metal ions deposit on the surface of the magnet, forming a layer of metal plating.

According to different product requirements, neodymium magnets can choose a variety of electroplating processes and coatings.The main electroplating coatings used for neodymium magnets are nickel and zinc, as these two coatings are the most suitable for direct electroplating on the surface of neodymium magnets.If multiple layers of coatings are used, coatings of other materials are generally electroplated after nickel plating.

3.Type of plating

Nickel: Nickel has strong corrosion resistance and can be exposed to high humidity in the atmosphere for a long time.However, as a material with high magnetic permeability, the plating layer has a certain shielding effect on the magnet.The shielding effect is more pronounced on some thin-shaped magnets.The nickel plating has higher polish and a distinct metallic luster, making it suitable for customers with aesthetic requirements.

Zinc: Zinc is very susceptible to chemical reactions with acidic substances, so its corrosion resistance is poor.However, compared to nickel, its cost is lower, making it suitable for customers with limited budgets and low corrosion resistance requirements.

Nickel-copper-nickel: Three-layer electroplating process is used, which has stronger corrosion resistance and can cope with most extreme environments.The copper plating layer is relatively soft and has low porosity, which can effectively improve the bonding force between the plating.

Nickel-tin: Tin has a soft texture and low melting point.By adding a tin coating to the magnet, we can make the magnet solderable.

Here are some common plating data:

PlatingSymbolPlating Thickness(μm)Salt Spray Test(h)HAST(h)
Nickel (barrel plating)Ni5-204848
Nickel (hanging plating)Ni5-201648
nickel-copper-nickel(barrel plating)Ni-Cu-Ni5-204848
Nickel-Copper-Nickel(hanging plating)Ni-Cu-Ni5-201648
ZincZn4-152424
Color ZincColor-Zn4-157248
Nickel-TinNi-Sn5-207296
Nickel-GoldNi-Ag5-207296
Nickel-SilverNI-Au5-207296
Nickel-Copper-Nickel-TinNi-Cu-Ni-Sn5-207296

Contact us:Contact | HQ Magnet (hq-magnet.com)

Learn more:Electroplating – Easy DIY Nickel, Copper, Zinc Plating – YouTube