Magnet Coating & Plating Options – Surface Treatment for Neodymium Magnets
Magnet coating is very important protection for neodymium magnet. Surface treatment is a process applied to the surface of a material to make it better in some way, for example by making it more resistant to corrosion or wear.
Corrosion can cause unprotected magnets to spall off a surface layer, or to crumble into a powder. Use of protective surface treatments such as gold, nickel, zinc, and tin plating and epoxy resin coating can provide corrosion protection.
Coating makes brittle permanent magnet more durable; multilayered metal plating like NiCuNi will improve the magnets resistance to chipping and wear, particularly around corners.
Harsh environments like salt and humidity in regions near the ocean can’t be ignored while choosing a coating.
The most common type of plating Nickel (Ni-Cu-Ni) is mainly for conventional environment and has proven to be very resilient when subjected to normal wear and tear. However it will be corroded in prolonged exposure to salt water, salty air, or harsh chemicals.
Everlube is a new coating appearing in recent years which will provide excellent resistance to heat and viscous properties and can be used on auto parts.
If coating can’t help, low weight loss magnet (hast magnet) is also a good solution.
Do all permanent magnets need to be plated?
No. Only rare earth magnet which is extremely brittle and also vulnerable to corrosion, is usually plated or coated to protect it from breaking, chipping, or crumbling into powder.
There are two types of rare earth magnets: neodymium magnet and samarium–cobalt magnet. The former is more vulnerable to oxidation than the latter.
Basically, there are five kinds of surface treatment that can be applied to permanent magnets.
Electrolytic plating
To make cathode electrophoresis by chemical principle, it is a common surface treatment process in the world currently.
a. salt spray test for 48 hours
b. constant temperature and humidity for 240 hours
c. good oil resistance and solvent resistance.
d. smooth surface, beautiful appearance
Anti-rust oil
To coat with a layer of anti-rust oil film evenly on the surface of product by the impregnation method. It can improve anti-rust capability without change of the appearance and size of product. It is particularly suitable for small-bore product
a. efficiency
b. simple process
Spray
To spray anti-corrosion coating evenly on the surface of product by spray principle. It’s especially used on small product with the weight less than 1 gram, or the outer diameter less than 5mm.
a. salt spray test for 24 hours
b. constant temperature and humidity for 240 hours
c. efficiency & high pass rate
d. good consistency
Plastic
The most corrosion resistant, thicker than other plating, mold required to create the plastic shell.
Special treatment
To permeate special glue into the gaps of product by negative pressure method. It is suitable for products which work in the oil or solvent environment.
a. seal porous surfaces
b. increase product strength
c. work long time in the oil or solvent environment
| Coating Type | Thicknes | Color | PCT | Salt Spray Test | Advantage |
| NiCuNi | 10-20μm | Bright Silver | > 48-72 H | > 24-72 H | excellent humidity heat & salt spray resistance |
| Epoxy | 10-30μm | Black or Grey | – | > 72-108 H | excellent humidity & adhesion heat & salt spray resistance |
| Coloured Zn | 4-8μm | Shining colour | – | > 48-72 H | excellent salt spray resistance |
| Zn | 4-8μm | Bright blue | – | > 24-48 H | regular protection applied to most products |
| Everlube | 8-20μm | Yellow | > 72 H | > 96 H | excellent salt spray resistance and adhesion |
| Black Nickel | 10-20μm | Bright Black | > 72 H | > 48-96 H | excellent humidity heat & salt spray resistance |
| Passivation / Phosphorization | ≤ 1μm | Dark grey | – | ≤ 2.5 H emerge in 3% NaCl liquor | temporary protection |
| Sn | 10-25μm | Silver | > 48 H | > 36-72 H | excellent humidity heat & salt spray resistance |
| Au | 10-15μm | Golden | > 48 H | > 12 H | good looking |
| Ag | 10-15μm | Silver | > 48 H | > 12 H | good looking |
| Chemical Nickel | 10-30μm | Bright Silver | > 72 H | > 96 H | excellent humidity heat & salt spray resistance |
| Organic Aluminium | 6-20μm | darkish silver | > 48 H | > 288 H | excellent humidity heat & salt spray resistance |
| Vacuum Aluminum | 10-30μm | Bright Silver | > 48 H | > 288 H | excellent humidity heat & salt spray resistance |
Remark:1. The time for salt spray test in the table is obtained after some special process. We make magnet coating by conventional process unless otherwise specified. | |||||