Electroplating

Electroplating is the most widely used finishing method, zinc is electro deposited onto the base material and the zinc corrodes in preference to the base material.

To enhance the corrosion resistance of the zinc the surface can be given a conversion coating or passivate.

These coatings can contain hexavalent chrome (which is now a controlled material under the EEC’s End of life vehicle legislation). In the majority of cases the hexavalent chrome can be replaced with the harmless trivalent chrome, but this has a detrimental effect on the corrosion resistance. In these cases this can be further improved by the use of the Leach Seal process (JS500) or lacquers.

Hydrogen Embrittlement

All components made from steel which are subject to chemical or electro-chemical treatments in the course of the coating process may absorb hydrogen which is evolved during these processes. This absorbed hydrogen can cause premature failure if the component is made from higher tensile steel.

Parts are usually considered to be at risk if they have a tensile strength equal to or greater than 1050 MPa, 1000 N/mm2 or 65 tons/sq.in. (T class imperial fasteners and above) or have a hardness greater than 320 vpn. (10.9, fasteners and above).

Baking parts after coating will minimise the risk of failure, this process can never be guaranteed to be completely effective.

Additional reading – Extract from ISO 4042:1999


Mechanical Plating

Degreased parts are placed in a drum with a mixture of glass beads and zinc powder. The beads cold weld the zinc to the components. The parts can then be passivated to give various levels of corrosion protection.  This process avoids the risk of Hydrogen Embrittlement.

Organic Coatings

These consist of a coloured pigment bonded with a heat curing polymer giving good corrosion resistance, controlled lubricity high wear resistance and no risk of Hydrogen Embrittlement.

Phosphating

Slight corrosion protection, used as an undercoat prior to painting, with the addition of oil increased corrosion protection can be achieved.

Hot Dip Galvanising

Products are immersed in molten zinc within temperature range 440 – 470 deg.C Coating thicknesses are 40 microns+ giving very high protection against corrosion.

Coating

Colour

Corrosion Resistance (Salt Spray Hrs)

CR6
Free

Potential for Hydrogen Embrittlement

ELECTROPLATING

Zinc + heavyweight trivalent passivate + top coat

Silver-iridescent

96w 384r

Yes

Yes

Zinc + yellow + top coat

Pale yellow

180w 252r

No

Yes

Zinc + clear

Silver

24w 96r

Yes

Yes

Zinc + yellow

Yellow

96w 192r

No

Yes

Zinc + heavyweight passivate

Iridescent

96w 240r

Yes

Yes

Zinc, no passivate

Silver

48r

Yes

Yes

Zinc + black

Black

72w 192r

No

Yes

Zinc + olive drab

Green – brown

168w 360r

No

Yes

Zinc + heavyweight passivate + nano particles

Silver

200w 600r

Yes

Yes

Zinc clear  + top coat

Silver

96w 240r

Yes

Yes

Zinc nickel yellow

Yellow-brown

480w 1000r

No

Yes

Zinc nickel + heavyweight

Purple-blue

120w 720r

Yes

Yes

Zinc nickel + heavyweight passivate + top coat

Silver-blue

144w 1000r

Yes

Yes

Zinc nickel + black

Black

240w 720r

Yes

Yes

Zinc nickel no passivate

Silver grey

720r

Yes

Yes

Zinc iron trivalent black

Black

500

Yes

Yes

Zinc iron trivalent clear

Clear

500

Yes

Yes

Zinc iron hexavalent black

Black

240w 480r

No

Yes

um (bright ni cr)

Silver metallic

72+

Yes

Yes

Nickel/black chromium (black ni cr)

Black

72+

Yes

Yes

Nickel

Pale yellow

72

Yes

Yes

Magni 560 (on zinc plate)

Silver-grey

840r

Free

No

MECHANICAL

Zinc trivalent heavyweight

Iridescent

48w 120r

Free

No

Zinc trivalent heavyweight + seal

Iridescent

 

 

 

Almac® (Zinc-Al)

Matt silver

200w 480r

Free

No

Inverplex (Zinc-Tin)

Matt silver

72w 240r

Free

No

Zinc trivalent TT15

Iridescent

 

 

 

Zinc chromate

Yellow

 

 

 

SPECIALIST COATING

Dry film lubricants

Clear, grey, black

Variable

Free

No

Phosphate -manganese

Grey

24+

Free

Yes

Phosphate - zinc

Grey

24+

Free

Yes

ORGANIC

Cathodic electrocoat

Black

1000r

Free

Slight

E-Cote®

Black

72r

Free

No

E-Cote® + seal

Black

120r

Free

No

Xylan®

Black, blue

144+r

Free

No

Xylan® Spray

As required

240+r

Free

No

Spray Painting

As required

As required

-

No

ZINC FLAKE

Geomet®

Silver-grey

240-1500r

Free

No

Delta Protekt®

Silver-grey

240-840r

Free

No

Magni 565

Silver-grey

840r

Free

No

Zintek® / Tintek® Top / Techseal®

Silver-grey

840

Free

No

TOP COATS -  Top coats can be applied to most coatings to modify colour and / or frictional coefficients. Some top coats also enhance corrosion performance of electro zinc and zinc flake base coatings.

Delta Coll® GZ

Various colours

 

 

 

Magni B18

 

 

 

 

Finigard® 105

 

 

 

 

TNT 15

Clear

 

 

 

Hydroclear lacquer

 

 

 

 

PS100

Leach seal

 

 

 

JS500

Leach seal

 

 

 

TT15

lubricant