Coatings for magnets

Samarium Cobalt, Alnico, and Ceramic materials are corrosion resistant, and do not require to be coated against corrosion. Alnico is easily plated for cosmetic qualities, and Ceramics may be coated to seal the surface, which will otherwise be covered by a thin film of ferrite powder (although not a problem for most applications).

Neodymium Iron Boron magnets are susceptible to corrosion and consideration should be given to the operating environment to determine if coating is necessary. Nickel or tin plating may be used for Neodymium Iron Boron magnets, however, the material must be properly prepared and the plating process properly controlled for successful plating. Plating houses  experienced in the plating of NdFeB materials are difficult to locate, and must be furnished with the necessary information for proper preparation and control of the process. Aluminum chromate or cadmium chromate vacuum deposition has been successfully tested, with coating thickness as low as 0.0005". Teflon and other organic coatings are relatively inexpensive and have also been successfully tested. A further option for critical applications is to apply two types of protective coatings or to encase the magnet in a stainless steel or other  housing to reduce the chances of corrosion.

Technics

classification

brightness

Technics explanation

Technics
Characteristics

Application
Situation

               Test Item and test method

1

2

3

4

5

Appearance

NSST
(neutral salt spray test)

Coating thickness
(μm)

Pct test
(hours)

Bonding force test
(thermal shock)

Goodness

Badness

Normal
Electroplated
Ni

Ni

Bright

Aggraded with
One or
two layer
of Ni from
Ni-plating groove

Good
Look, easy to control in operation

Erode-resistant is worse than NiCuNi and double Ni

Can be used in most circumstance with not very strict requirement

Colour and luster uniformity, no rust, no water spot and so on; no bubble、crack 、hole and burrs which is visible on surface..

>=48 h

>=10

>=48

√

Semi-bright

Electroplated
NiCuNi

NiCuNi

Bright

After one layer of Ni coating, then coat bright or dark Cu, then coat bright or a sub-bright Ni

Better look, with little holes on the surface, and good erode-resistant

Operation control is more fussy

Suitable for the circumstance with high-protection and high-decoration

>=72 h

>=10

>=48

√

Semi-bright

Electroplated blue-
white
Zn

Zn

White

Surface  handled with chromate,

Erode-resistant and color-change-resistant is better than normal Zn

Colour and luster uniformity is hard of under control

Suitable for a little erodent-trend and a little damp circumstance

Take on uniform blue and white , allow with some light intervene  colour, no rust, no water spot and so on; no bubble、crack 、hole and burrs.

>=24h

>=6

-

-

passivated film looks very clear and light blue

blue

Surface  handled with trivalent chromate, passivated film looks  light blue

Electroplated Color Zn

Color Zn

Surface  handled with chromate, passivated film looks rainbow color

Good erode-resistant

passivated film is not very good with rubbing.

With good protection, and can be used in damp and hot industrial circumstance

Surface looks clear and bright iridescence, not allowed the products attach with each other. No bubble、crack 、hole and burrs.

>=72h

>=8

-

-

Trivalent Chromate color Zn

Surface  handled with trivalent chromate, passivated film looks rainbow color or blue

Very good erode-resistant

Surface looks clear and bright iridescence or blue, not allowed the products attach with each other. No bubble、crack 、hole and burrs.

>=48h

>=8

-

-

Passivated

/

Use phosphate with An, Mn, Ca, then  form indiscerptible surface.

Low cost, less equipment, and easy operation

Erode-resistant is not very good

Can be used in dry circumstance in short term.

Not allowed yellow and  gray crystalloid

>=2h

3-5

-

-

Electrophoresis
Paint
(Epoxy)

/

In water-solubility lacquer, use electrophoresis, aggraded with epoxy or propylene

Good coating effect and coating  uniformity, and erode-resistant is good

Easy to dissolve and can not endure the damp circumstances, the control is difficulty.

Use during the circumstance with electric isolation or industry erode gas.

Looks full and bright and not allowed holes, shell, hang trace and so on.

>=48h

10-30

√

-