Formerly Emhart Teknologies & Infastech

Technical Information

Corrosion Resistance

For increased corrosion resistance and for customers' specific requirements, a range of standard finishes is available. The matrix below compares the various features of these finishes and can be used as a guide to selecting the most appropriate surface finish for an application.

Note

European Directive 2000/53/EC Vehicle End of Life (ELV) Legislation states that hexavalent chromium (Cr6+), lead, mercury and cadmium are substances banned from vehicles marketed after 1 July 2007. Our fasteners do not contain cadmium or mercury.

However, yellow passivation treatment of zinc and zinc alloy plating contains hexavalent chromium (Cr6+) and some hot tin dipped coatings contain lead.

In conjunction with metal finishing companies, the automotive industry, and the electronics industry, we have developed finishes that are free from both Cr6+ and lead.

 

Light

light

 

Moderate

moderate

 

Severe

severe

 

Very Severe

very severe

 

Corrosion
Conditions

Galvanic
Corrosion

Hexavalent
Chromium

Electrical
Conductivity

Temperature
Resistance

Appearance

Availability

Cost

Zinc plate
+ yellow
passivation

Light

Refer
to Chart

Yes

Conductive

Moderate/
Low

Iridescent
Yellow

Moderate/
Good

Low

Zinc/nickel
plate + yellow
passivation

Severe

Refer
to Chart

Yes

Conductive

Good

Iridescent
Yellow

Moderate/
Good

High

Zinc plate +
clear
passivation

Moderate

Refer
to Chart

No

Conductive

Moderate

Clear/
Metallic
Blue Tinge

Good

Low

Zinc plate +
clear
passivation +
sealer

Moderate

Refer
to Chart

No

Conductive

Moderate

Clear/
Metallic
Blue Tinge

Good

Moderate

Zinc/nickel
plate +
clear
passivation

Severe

Refer
to Chart

No

Conductive

Good

Clear/
Metallic
Blue Tinge

Good

High

Zinc/nickel
plate +
black
passivation

Severe

Refer
to Chart

No

Conductive

Good

Black

Good

High

Zinc plate +
Deltaseal

Moderate

None

No

Non
Conductive

Moderate

Black
Silver

Good

Moderate

Zinc/nickel
plate +
Deltaseal

Severe

None

No

Non
Conductive

Good

Black
Silver

Good

High

Phosphate
and
Deltaseal

Moderate

None

No

Non
Conductive

Moderate

Black
Silver

Good

Moderate

Zinc/nickel
plate +
KTL

Very Severe

None

No

Non
Conductive

Good

Black

Moderate

High

Light

Typically indoors and warm dry atmospheres.

Moderate

Typically indoors where moisture can occur. Outdoors in mild corrosive conditions.

Severe

Typically outdoors in moderate corrosion conditions for example light industrial and possibly external vehicle applications.

Very Severe

Typically outdoors in severe corrosive conditions for example marine, industrial or vehicle engine compartment or under body.

Galvanic Corrosion

Galvanic corrosion occurs when two dissimilar metals are in close contact with an electrolyte, a medium through which an electrical current can flow. The presence of water as moisture can act as an electrolyte. The rate of corrosion depends upon the differences in electrical potential, or anodic-cathodic relationship, of the metals in the joint as defined by the Galvanic Series of Metals & Alloys. (See below).

A highly anodic metal in contact with a highly cathodic metal will corrode much more quickly than two highly cathodic metals or when the metals are closer together in the galvanic series.

When corrosion occurs it is the anodic metal most likely to corrode and the cathodic metal least likely to corrode.

To reduce the likelihood of galvanic corrosion in a fastened joint, it is recommended that the designer choose metals that are grouped together in the galvanic series chart. If that is not possible, other recommendations are:

  • Select metals which are as close together in the chart as possible.
  • Provide a barrier between the metals, such as paint, non-metallic washer, gaskets or jointing compound.
  • Design the fastener as the cathode so that the cathodic area is as small as possible to the anode area.
  • Use a metallic finish on the fastener that is close on the chart to the mating metal.
  • Use a non-conductive and inert finish on the fastener.

Galvanic Series

Anodic End (Most Likely to Corrode)

  • Magnesium and its alloys
  • Zinc and zinc plating on steel
  • Aluminium Alloys
  • Cadmium
  • Mild Steel & Iron
  • Cast Iron
  • 13% Chromium stainless steel (active)
  • 18-8 Austenitic stainless steels (active)
  • Tin-Lead, Lead and Tin
  • Nickel (active)
  • Brasses
  • Copper
  • Bronzes
  • Cupronickel Alloys
  • Silver Solder
  • Nickel (passive)
  • Iron-chromium alloys (passive condition)
  • 18-8 austenitic stainless steels (passive condition)
  • Silver
  • Titanium
  • Gold and other precious metals

Cathode (Least Likely to Corrode)