Electroplated zinc based on BS7371-3: 1993

 

Electroplated zinc with an RoHS compliant (trivalent) chromate passivation offers basic corrosion protection and is inexpensive. The major disadvantage of any electroplating process is that it can cause hydrogen embrittlement in fasteners with a tensile strength greater than 830Mpa.

As standard, all fasteners that are case hardened and all fasteners with a property class of 8.8 or higher are heat treated after electroplating to help reduce the risk of hydrogen embrittlement. This process is called de-embrittlement, but it does not guarantee that the risk of hydrogen embrittlement is removed completely. If any risk of hydrogen embrittlement is unacceptable than a non-electroplated finish should be considered.

 

 

Chromate treatment: clear (standard)

Nominal thread diameter mm Typical thickness Zinc corrosion (white) Rust (red) Appearance Protection Typical applications
up to 2mm 3 microns 2 hours 12 hours Transparent with slight bluish tinge Slight, for example against staining during handling or against high humidity in mildly corrosive conditions  
2.5mm to 8mm 5 microns 6 hours 24 hours
10mm to 20mm 8 microns 6 hours 48 hours
over 24mm 12 microns 6 hours 72 hours
 

 

Chromate treatment: bleached

Nominal thread diameter mm Typical thickness Zinc corrosion (white) Rust (red) Appearance Protection Typical applications
up to 2mm 3 microns 6 hours 12 hours Transparent with slight iridesence Slight, for example against staining during handling or against high humidity in mildly corrosive conditions  
2.5mm to 8mm 5 microns 12 hours 36 hours
10mm to 20mm 8 microns 24 hours 72 hours
over 24mm 12 microns 24 hours 96 hours
 

 

Chromate treatment: black

Nominal thread diameter mm Typical thickness Zinc corrosion (white) Rust (red) Appearance Protection Typical applications
2.5mm to 8mm 5 microns 12 hours 48 hours Black with slight iridesence Slight, for example against staining during handling or against high humidity in mildly corrosive conditions  
10mm to 20mm 8 microns 24 hours 72 hours
over 24mm 12 microns 24 hours 96 hours
 

 

Chromate treatment: iridescent

Nominal thread diameter mm Typical thickness Zinc corrosion (white) Rust (red) Appearance Protection Typical applications
up to 2mm 3 microns 6 hours 12 hours Yellow iridesence Considerable, including organic vapours  
2.5mm to 8mm 5 microns 12 hours 36 hours
10mm to 20mm 8 microns 24 hours 72 hours
over 24mm 12 microns 24 hours 96 hours
 

 

Chromate treatment: opaque

Nominal thread diameter mm Typical thickness Zinc corrosion (white) Rust (red) Appearance Protection Typical applications
up to 2mm 3 microns 24 hours 24 hours Olive green, shading to brown or bronze Considerable, including organic vapours  
2.5mm to 8mm 5 microns 72 hours 96 hours
10mm to 20mm 8 microns 96 hours 144 hours
over 24mm 12 microns 96 hours 168 hours
 

Notes

As a result of the new EoLD, new trivalent finishes have been developed which can improve corrosion resistance. Some of these can now achieve up to 1,000 hours to red eust. For more details contact your nearest TR location.

Adding sealer to electro zinc finish will enhance performance (excluding opaque).

Unthreaded components - please refer to ISO 12329.

Corrosion resistance figures are based on Standard Salt Spray Test under laboratory conditions.